ion exchange thesis
TRANSCRIPT
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
DECLARATION
I, William C. Miinga do hereby declare that this project is entirely my own, and that
all the sources of information towards this project has been duly acknowledged,
and that it has never been done previously or submitted at this institution or any
other for similar purpose.
Author’s signature: ……………….................. Date: ……………………………
MR MIINGA WILLIAM
Supervisor’s signature: ……………………… Date: …………………………
MISS MWAMBA PRECIOUS
Supervisor’s signature: ………………………. Date: ………………………….
MR KALUNGA KELVIN
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
DEDICATION
I dedicate this final year project report to my late parents Mr. Albert Miinga and Mrs.
Kolida m’hango Miinga and my Aunt Mrs. Susan m’hango mwale for their tireless
efforts in supporting and encouraging me throughout my academic endeavors, my
family members and my special friend Moira Chanza for the inspiration and
encouragement during my stay at the Copperbelt University. May our Lord and
savior Jesus Christ richly bless you all.
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
ACKNOWLEDGEMENT
May I wish to acknowledge each and every one who gave me both physical and
moral support during my stay at CBU, but first and foremost I want to thank the
almighty GOD for taking care of me throughout my entire life especially at the
Copperbelt University.
I would like to thank my supervisor Miss Mwamba (CBU) for the supervision
rendered to me and big thanks go to the Management of Chambishi Metals Plc. for
giving me the opportunity to carry out my final year project in their company. I
greatly owe my heartfelt appreciation to the following individuals for the support
rendered which enabled me acquire credible appreciation of chambishi metals
research and development as well as analytical departments operations. The
Training coordinator Mr P. mumba, am humbled to see that you are really
committed to the development of students career, this is as it should be. To my
boss Mr K. Kalunga and Mr E. Bwalya, a brother’s keeper and trainers is just the
best way to describe both of you. You received me with open hands during my stay
at chambishi metals and I saw great men in you that knew exactly what students
need and you proactively facilitated.
I am particularly aware that, there are many more people who in one way or the
other, either directly or indirectly made it posible for me to complete my industrial
attachment sucessfully. I do not underestimate anybody and their efforts, I have
recognised everybody duely and with all due respect despite having not listed
everyones name,to you all I say ’’ Well done Team’’ and may God bless you.
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
ABSTRACT
Chambishi Metals plc has increased production by putting up new infrastructures
like the Copper Solvent Extraction (CuSX) plant as well as increasing the capacity
of the Copper Tank House but the Cobalt circuit has remained the same.
Currently, Chambishi Metals Plc treats concentrates coming from a mine in DRC
Congo known as Tenke-Fungurume Mine. These concentrates contain both Co and
Cu metals, and they are Camec (Boss) and Tenke concentrates. And also Nkana
Mopani concentrates and Nampundwe pyrites are also treated at the roaster plant
as supplement (when Sulphur from the two concentrates is not adequate for SO2
production which is used in H2SO4 acid production). Due to the difference in their
chemical compositions, these concentrates are treated in different ways. Copper
removal in the purification circuit is currently being achieved by electro stripping at
the electro-stripping section of copper solvent extraction and the residue copper is
precipitated in the cleanup train. Zinc rejection is being achieved by solvent
extraction using Di-2-EthylHexyl Phosphoric Acid (D2EHPA) as an extractant and
the residue zinc is precipitated in the cleanup train. Iron is precipitated in the ferric
and clean up trains.
The objective of the project was to establish whether the resin lewatit vp oc 1026
can be used to remove zinc impurities from the cobalt streams of “Chambishi
Metals plc.” purification circuit by the use of Ion Exchange. Laboratory tests were
carried out to verify this. This was done by loading the resins with TM2 overflow
and optimizing the cobalt elution with time by eluting with 5.6 g/l and 9.4 g/l
sulphuric acid and optimizing the zinc elution with time by eluting with 93.9 g/l and
110 g/l sulphuric acid.
Test works were carried out by passing cobalt rich solution through a 120ml bed
volume of lewatit vp oc 1026 at a flow rate of 10BV/hr and 7.5BV/hr during the
optimized cycle at ambient temperature. The pH and temperature of the effluent
were measured until the breakthrough was reached.
During loading, the feed pH dropped from the initial 3.3 at ambient temperature to
a pH value of about 2, after which it rose in the first 600 minutes at the slower rate
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until saturation was reached. The loading of zinc on the resin was efficient as
breakthrough took place only after 1500 minutes i.e. after 7.2 litres of feed solution
had been passed through the resins.
The percent split elution shows that eluting with 5.6 g/l sulphuric acid (H2SO4), of the
Iron, Copper, Zinc and Cobalt that was loaded on the resin, an average of 8 % Cu
and 2.5% Zn, 93% Co and 8 % Fe went to the Cobalt eluate, which is a good
recovery for a stream that is recycled back into the plant, and 91.5 % Cu, 97.6 %
Zn, 6.5 % Co and 92.5% Fe went to the Zinc eluate were it is supposed to go when
110g/l eluant (H2SO4) is used. Here the split was very good. With 9.4 g/l (H2SO4) of
the Iron, Copper, Zinc and Cobalt that was loaded on the resin, 94% Zn went to the
Cobalt eluate, a stream that is recycled back in the plant. Hence with 9.4g/l eluant
the split was very poor as compared to the Cobalt eluate at 5.6 g/l H2SO4.
The optimum Cobalt loading was achieved at pH 2.5 and flowrate 7.5BV/hr for
1800 minutes. Optimum Cobalt elution was achieved with 5.6 g/l sulphuric acid.
The optimum cobalt-zinc elution was done for 72 minutes. Based on the results the
current purification circuit flowsheet (Figure 2.1) can be replaced by the proposed
purification circuit flowsheet (Figure 4.9). The testworks thus far shows that the
resin lewatit vp oc 1026 can be used to remove zinc impurities from the cobalt
streams of chambishi metals purification circuit by ion exchange.
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Table of Contents
DECLARATION.........................................................................................................................iDEDICATION...........................................................................................................................iiACKNOWLEDGEMENT........................................................................................................iiiABSTRACT.............................................................................................................................ivTable of Contents....................................................................................................................viList of Figures.......................................................................................................................viiiList of Tables...........................................................................................................................ixCHAPTER ONE.......................................................................................................................21. INTRODUCTION......................................................................................................31.1. PROJECT BACKGROUND.....................................................................................41.2. PROJECT MAIN OBJECTIVE................................................................................41.3. PROJECT SPECIFIC OBJECTIVES.....................................................................4CHAPTER TWO......................................................................................................................52.1. PLANT OPERATION PROCESS DESCRIPTION...............................................6
2.1.1. ROASTER PLANT................................................................................................62.1.2. COPPER SOLVENT EXTRACTION (Cu- SX) PLANT....................................72.1.3. COPPER TANKHOUSE.......................................................................................92.1.4. LIME PLANT..........................................................................................................9
2.1.4.1. Quick Lime.....................................................................................................102.1.4.2. Rock Lime.....................................................................................................10
2.1.5. COBALT PLANT OPERATION PROCESS DESCRIPTION.........................11a) Cobalt purification circuit....................................................................................12b) Cobalt tank house...............................................................................................29
2.2. CURRENT FLOW SHEET AT COBALT PURIFICATION PLANT...................33CHAPTER THREE................................................................................................................34
3.1. BASIC CONCEPTS OF ION EXCHANGE.............................................................353.2. TYPES OF RESINS..................................................................................................37
3.2.1. CATION AND ANION EXCHANGE RESIN..................................................373.2.2. HEAVY – METAL – SELECTIVE CHELATING RESINS...........................403.2.3. LEWATIT VP OC 1026 RESINS...................................................................41
3.3. TECHNOLOGY / EQUIPMENT DESCRIPTION................................................413.3.1. BATCH AND COLUMN EXCHANGE SYSTEMS.......................................413.3.2. ION EXCHANGE RESINS AND COLUMNS...............................................423.3.3. FIXED – BED COLUMN SYSTEMS.............................................................42
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
3.3.4. INTEGRATED AGAINST MODULAR DESIGNS........................................433.3.5. SINGLE Vs DUPLEX COLUMN OPERATION...........................................443.3.6. COUNTER FLOW Vs COCURRENT FLOW / REGENERATION...........443.3.7. OTHER EQUIPMENT / DESIGN CONSIDERATION................................453.3.8. REGENERATION PROCEDURE.................................................................463.3.9. THE MASS TRANSFER ZONE (MTZ).........................................................47
CHAPTER FOUR..................................................................................................................48APPARATUS AND METHODOLOGY................................................................................484.0. APPARATUS AND EXPERIMENTAL PROCEDURES.....................................49
4.1. APPARATUS AND REAGENTS USED...............................................................494.2. SAMPLES................................................................................................................494.3. EXPERIMENTAL PROCEDURES.......................................................................49
4.3.1. LOADING..........................................................................................................494.3.2. ELUTION..........................................................................................................50
CHAPTER FIVE.....................................................................................................................51RESULTS AND DISCUSSIONS..........................................................................................515.1. 1st CYCLE.................................................................................................................52
5.1.1. FIRST CYCLE SPLIT EFFICIENCY...................................................................555.2. 2ND CYCLE...............................................................................................................56
5.2.1. SECOND CYCLE SPLIT EFFICIENCY...........................................................595.3. 3RD CYCLE...............................................................................................................60
5.3.1. THIRD CYCLE SPLIT EFFICIENCY................................................................635.4. PROPOSED FLOWSHEET FOR Zn REMOVAL...............................................65CHAPTER SIX.......................................................................................................................66CONCLUSIONS AND RECOMMENDATION...................................................................666.1. CONCLUSIONS......................................................................................................676.2. RECOMMENDATIONS..........................................................................................677. APPENDICES.........................................................................................................68REFERENCES......................................................................................................................71
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
List of Figures
Figure 1.1a: Flow sheet showing material flow at Quicklime Preparation
Figure 1.1b: Flow sheet showing material flow at rock lime Preparation
Figure 1.2: Flow diagram showing material movement at Ferric Train
Figure 1.3a: Diagram showing the preparation and movement of E24 solution.
Figure 1.3b: Showing the preparation and movement of E24 solution.
Figure 1.3: Showing the flow of material at the Co tank House
Figure 1.4: Flow sheet showing liquor movement at Zn SX plant
Figure 1.5: Flow sheet showing liquor movement at Clean-up Train
Figure 1.6: showing the movement of liquor at hydroxide train
Figure 1.7: Showing the movement of liquor at resolution train
Figure 1.8: Showing the movement of liquor in clarifier/carbon columns
Figure 1.9: Showing the movement of liquor at IONEX.
Figure 2.0: Showing the flow of material at the Cobalt tank House.
Figure 2.1: Current Chambishi Metals Cobalt Plant Flow Sheet
Figure 2.2 Schematic sections through a cation exchange resin
Figure 2.3 Discharge capacity vs pH profile for weak acid and weak base resin
Figure 4.1Loading profile for Co, Cu, Zn and Fe at 10BV/hr.
Figure 4.2Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr.
Figure 4.3 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr.
Figure 4.4 Loading profile for Co, Cu, Zn and Fe at 10BV/hr.
Figure 4.5 Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr
Figure 4.6 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr.
Figure 4.7 loading profile for Co, Cu, Zn and Fe at 7.5BV/hr
Figure 4.7 Cobalt elution profile using 5.6 g/l H2SO4 at 5BV/hr
Figure 4.8 Zinc elution profile using 110 gpl H2SO4 at 5BV/hr.
Figure 4.9Proposed flow sheet for the removal of Zn from TM2 overflow
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
List of Tables
Table 2.1- selectivity of ion exchange resins in order of decreasing preference
Table 4.1 Percentage split of cobalt eluate using 9.4 gpl H2SO4
Table 4.2 Percentage split of Zinc eluate using 93.9 gpl H2SO4
Table 4.3 Percentage split (2nd cycle) of Cobalt eluate using 9.4 gpl H2SO4
Table 4.4 Percentage split (2nd cycle) of Zinc eluate using 93.9 gpl H2SO4
Table 4.6 percentage split (3rd cycle) of zinc eluate using 110gpl H2SO4
Table 4.5 percentage split (3rd cycle) of cobalt eluate using 5.6 gpl H2SO4
Table 6.1 Loading profile results in the first stage
Table 6.1.2 Cobalt elution results 1st stage
Table 6.1.3 Zinc elution profile results 1st stage
Table 6.2 Loading profile results in the 2ND CYCLE
Table 6.2.2 Cobalt elution results 2nd stage
Table 6.2.3 Zinc elution profile results 2nd stage
Table 6.3 Loading profile results in the third stage
Table 6.3.2 Cobalt elution profile results 3nd stage
Table 6.3.3 Zinc elution profile results 3nd stage
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
CHAPTER ONEINTRODUCTION
1. INTRODUCTION
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
This project was successfully performed at Chambishi Metals plc situated along
Kitwe – Chingola road on the Copperbelt province of Zambia.
The cobalt plant at Chambishi Metals is currently processing two concentrates a
mixture of copper and cobalt from Congo DR. Copper, Zinc, Iron and Nickel are
currently by product elements; only cobalt is the metal being processed for export.
TENKE and CAMEC are the trade names for the two concentrates which are being
processed. The two concentrates are very rich in cobalt and contain about 30-
40%Co, 5-10%Cu, 3-5%Fe and some other impurities like Zn, Ni and Mn.
The company’s main objective is to produce quality cobalt and copper at higher
recoveries and lower costs in the safest working environment. To achieve this
objective the company engages in different projects like carrying out test works to
improve on the removal of Zinc impurities from the Cobalt rich streams of the
purification circuit by Ion Exchange.
Chambishi Metals plc is divided into the following plants:
Roaster plant
Acid plant
Copper Tank House/ Lime plant
Copper Solvent Extraction
Cobalt Purification plant
Cobalt Tank House
Smelter plant(not operational)
The refinery plant consists of copper tank house, cobalt tank house and cobalt
purification. Currently, the company produces 3000 - 3600 tons of cobalt per
annum.
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1.1.PROJECT BACKGROUND
Chambishi Metals plc has four trains in the purification circuit namely ferric train,
clean up train, hydroxide train and resolution train. Each train acts as a purifying
aid in attaining exportable cobalt metal with a higher price on the world market.
The purpose of the trains is to remove iron, zinc, nickel and copper from the
process liquor solution coming from the Cu-SX plant and other recycled streams.
The ferric train consists of eight mechanically agitated tanks where material
gravitates through into the thickener (TM1). Iron is precipitated in the ferric and
clean up trains by changing the pH of the process liquor solution from Cu-SX plant
from pH 1 to pH (2-3). The overflow of thickener 1 is pumped to zinc SX plant for
zinc. Zinc Removal from TM1 O/F is achieved by solvent extraction using D 2EHPA
as an extractant and shell sol as a diluent and the residue zinc in the process liquor
solution from Zn-SX plant is precipitated in the clean-up train. The clean-up train is
responsible for the control of zinc in the thickener O/F at < 4ppm concentration. It
consists of five cascading vessels and a thickener (TM2). The overflow of thickener
2 is pumped to the hydroxide train.
1.2.PROJECT MAIN OBJECTIVE
To establish whether lewatit vp oc 1026 resins can be used to remove zinc
impurities from cobalt streams of the purification circuit of chambishi metals plc by
ion exchange.
1.3.PROJECT SPECIFIC OBJECTIVES
Optimization of Cobalt elution by eluting with 9.4 and 5.6 g/l sulphuric acid.
Optimization of zinc elution by eluting with 93.9 g/l and 110 g/l sulphuric
acid.
Propose a flow sheet for the removal of zinc from the cobalt stream.
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CHAPTER TWO
PLANT DESCRIPTION
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2.1. PLANT OPERATION PROCESS DESCRIPTIONCurrently, Chambishi Metals Plc treats concentrates coming from a mine in DRC
Congo known as Tenke Fungurume Mine. These concentrates contain both Co and
Cu metals, and they are Camec (Boss) and Tenke concentrates. Due to the
difference in their chemical compositions, these concentrates are treated in
different ways.
Between the two, Camec concentrate has got high tenors of Cu, therefore before it
can be treated for Co; it is first stripped-off Cu. This is done by leaching it at
Roaster Plant, and the pregnant leach liquor is sent to Cu-SX plant for Cu
Extraction i.e. the copper in the process liquor solution is removed by contacting it
with the organic solution. This is done to remove the copper in liquor so that it can
be electro-won at the copper tank house. Cu in Co electrolyte act as an impurity if
allowed to go to Co tank house, therefore, it is removed out of solution before it is
sent to Co Purification Plant. Tenke concentrate, is re-pulped and prepared right at
the purification plant.
Stripped liquor from Cu-SX plant and prepared Tenke cake are both pumped to Co
purification circuit for impurity removal. A pH based method of purification is
employed by using lime and sulphuric acid to remove impurities like Fe, Cu, Ni and
Zn. Zn is removed by solvent extraction (SX) process while Ni is removed by ion
exchange (IX). The purified and clarified solution is then pumped to Co Tank House
for Co electro-winning.
Co electro-winning is carried out using DC current across lead anodes and
stainless cathodes where Co is electroplated. The pulling cycle averages on 4
days. Electro-won Co is stripped and crushed into flakes which are degassed
under vacuum at temperatures of about 750-820oC to reduce hydrogen in the
metal to 5ppm or less. The degassed flakes are then burnished to remove scale
and surface oxidation. The product is then drummed in 250kg for shipment.
2.1.1. ROASTER PLANT
The roaster plant is the heart of chambishi metals. This is the plant whose main
aim is to obtain as much Cu/Co as possible in solution and the rest of the minerals
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
which are considered as impurities into solids.the major parameters in the roaster
include
pH
Pressure
Temperature.
O2 Blowing rate
a) BRIEF PROCESS DESCRIPTION
Chambishi Metals Plc treats several concentrates namely frontier mine
concentrate, boss mine concentrate, Nkana Mopani concentrate and nampundwe
pyrites. However, during the familiarization program the plant was only treating
frontier and boss mine concentrates. Due to the difference in their chemical
compositions, these concentrates are treated in different ways. The concentrates
are first stored in the vat ridge upon delivery by the trucks. The material is
thereafter taken to the bin flows at the roaster plant and then in the feeders where
they are blended according to the requirements of the process controllers and
transported by conveyor belts CV1 and CV2 to the slurry tanks and finally into the
roaster. In the roaster the operating pressure should be above 5% SO2, so as to
reduce on the loss of SO2 as fumes through the stack and the operating
temperature should be 6800 C.
b) LEACHING PROCESS AT ROASTER PLANT
During the leaching process the overflow together with the filtrate from the roaster
belt filter goes into TK30 and then to copper solvent extraction (Cu-SX) for
extraction of Copper. The sulphur that is produced from the roaster is compressed
and used in the production of concentrated sulphuric acid at the acid plant .The
underflow goes to the neutralization circuit.
2.1.2. COPPER SOLVENT EXTRACTION (Cu- SX) PLANT
This is the plant that is concerned with the extraction of copper from solution
preferentially by a solvent. The feed is the pregnant leach solution (PLS) from
roaster plant. The PLS is first received in the PLS pond to allow the total
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
suspended solids to settle. From the pond PLS is pumped to the mixer were it is
mixed with extractant in the diluent shell sol hence extraction commences. This
plant has two sections known as Cu-SX1 and Cu-SX2. There are generally two
major processes during copper processing at Cu-SX1
Extraction happens at area 500
Stripping happens at area 530
The first step is the extraction process in which the PLS (CuSO4) is contacted with
the barren organic (HR) through agitation method of contacting. PLS is pumped to
the dispersion overflow pump (DOP) where it is agitated and pumped to the spiral
tanks for uniform mixing of the organic and the PLS. The method of contact
between organic and PLS is counter-current. The extraction section comprises
three settlers E1, E2 and E3.From the spiral tanks the organic together with PLS
moves into E1 where the loaded organic (copper rich organic) is separated from
the raffinate (solution that remains after the copper has been removed from
PLS).The process continues in E2 up to E3 where the raffinate (H2SO4) exits while
the loaded organic (R2Cu) exits via E1 to the striping section. This process can be
summarized by the following equation;
CuSO4 (aq) + 2HR (org) ↔R2Cu (org) + H2SO4(aq) 1.0a
a) FACTORS AFFECTING THE EFFICIENCY OF EXTRACTION
PLS and organic ratio
pH
Flow rates of organic and PLS
Mixing intensity
b) STRIPPING
Stripping is the opposite of extraction. At the stripping section the loaded organic
(R2Cu) contacts the spent electrolyte (H2SO4) from purification plant counter-
currently. The SE strips copper from the loaded organic through the settlers S1, S2
and S3 leaving it barren. The barren organic (HR) goes back to the extraction
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section via S3 while the advance electrolyte (CuSO4) goes to copper tank house
for electro-winning of the copper via S1.
H2SO4 (aq) + R2Cu (org) ↔ 2HR (org) + CuSO4 (aq) 1.0b
2.1.3. COPPER TANKHOUSE
This is the part of the purification plant where dissolved Cu in liquor is electro won
out of solution.
Liquor from Cu-SX is pumped to area 460,where it is mixed with Gwar and then
into the cells where it is extracted onto the cathodes. The cathodes placed on the
anodes with direct current applied are dipped into the cells containing the advance
electrolyte. The cathodes are left for a week to allow the electro-wining process to
be completed. During the process of electro-winning there is strong fuming that is
suppressed by the use of plastic mist balls. After the cathodes have been removed
from the cells the copper is stripped off using the automated stripping machine.
The striping involves the use of steam for easy removal of copper from the
cathodes. After the cathodes have been washed the wash water is joined to the
pipes for the spent electrolyte which goes back to copper SX for further stripping of
copper from the loaded organic.
a) FUNCTIONS OF GWAR
To make the copper shiny
To make the copper soft
To make it easier to remove the copper from the cathode at the striping
machine.
2.1.4. LIME PLANTThis is the plant where both quicklime and rock lime are prepared from for use at
purification plant. It is divided into two major parts, that is, rock lime and quicklime
preparation areas.
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2.1.4.1. Quick Lime
This is an oxide alkali used for pH control of different streams in operation. It is
purchased from Ndola lime as calcium oxide (CaO). During its preparation, quick
lime is first charged to a jaw crusher where it is crushed and released into a bin
below the crusher. From the bin, lime mixes with water at a ball mill chute, and
enters the mill. In the ball mill, lime is ground to 75% passing 75microns to achieve
a quicklime solution of desired specific gravity and %solids. Discharge from the ball
mill collects into the sump and pumped into TK40, a stock tank. To pump this lime
to purification, specific gravity in terms of %solids is checked for and is supposed
to be >20% solids. When pumped to purification, quicklime reports to TK90, and is
usually at high temperatures of about >75oC.
Quicklime
HopperStoring bin
Vibrator
Crushed lime17-18%solids
Mill Chute
Water
>20% solids
To TK90 at Purification Plant
Figure 1.1a: Flow sheet showing material flow at Quicklime Preparation
2.1.4.2. Rock Lime
This is a calcium carbonate stone used for pH control during processing of different
materials. It is prepared in a similar way as quicklime except that there is no jaw
crusher involved with this one. However, this process involves the charging of rock
lime to a hopper which gravitates into a ball mill via a chute. Water is added to the
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Jaw Crusher
Ball Millsump
TK40Stock Tank
Sampling point for % solids
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
feed in the chute, where together, the material flows into the mill. This material is
ground to a specific required size, and the mixture let to flow into TK40, which is a
rock lime stock tank. From this tank, the prepared lime is pumped to TK130 at
purification plant with about 17-18% solids. Consider a simple flow sheet below:
Rock lime
Hopper
Vibrator
Water
To TK130 at Purification Plant With 17-18%solids
Figure 1.1b: Flow sheet showing material flow at rock lime Preparation
2.1.5. COBALT PLANT OPERATION PROCESS DESCRIPTION
The strip liquor, which is a bleed stream after copper removal, constitutes feed to
the cobalt recovery circuit. The stripped liquor from the copper SX plant is pumped
to the cobalt purification circuit for impurity removal. Impurity removal is done using
a pH based precipitation method using lime and sulphuric acid to remove impurities
like iron, copper and zinc. A solvent extraction process is employed in case of the
zinc impurity using D2EHPA as an extractant.
The purified solution from the purification circuit is pumped to the cobalt tank house
for cobalt electro-winning. Cobalt metal is won out of the purified and clarified
solutions. The cobalt metal electro-winning process is done by applying a direct
current across lead anodes and stainless Steel cathodes onto which cobalt is
deposited (plated out) from the electrolyte. The pulling cycle averages 4 days but
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Ball Mill Sump
TK40Stock Tank
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
may be adjusted to compensate for low deposition rates as a result of lower
operating current. In order to remove cobalt sulphate crystals, after pulling, the
cobalt is thoroughly washed in warm water before stripping the metal from the
stainless steel cathode blanks. The electro-won cobalt is crushed into +5mm to -
30mm flakes and the oversize material is recycled to the crusher and the undersize
is classified as fines and it is treated separately. The flakes are then degassed
under vacuum at 750 to 820oC in order to reduce hydrogen gas content in the
metal to 5ppm or less. In order to remove surface oxides and scale, the degassed
flakes are burnished and the product is then packed or drummed in 200kg or
250kg drums for shipment.
a) Cobalt purification circuit
The objective of the cobalt purification circuit is to purify and clarify the stripped
liquor from the cobalt SX in order to removal impurities like copper, nickel, iron,
zinc and sulphides. This is achieved by a pH based precipitation method using lime
and sulphuric acid (H2SO4). All absorption removes sulphides and organics where
activated carbons are used in the carbon columns. Nickel is removed by iron
exchange method.
Purified and clarified solution is pumped to the cobalt tank house for cobalt metal
electro-winning. Applying a direct current across lead anodes and stainless steel
cathodes onto which cobalt is plated out from the electrolyte carries out the cobalt
electro-winning. The cobalt is washed in warm water to remove cobalt sulphate
crystals before the metal is stripped from the stainless cathode blanks. The won
cobalt is crushed into flakes. Samples of flakes are chemically analysed for nickel,
manganese, lead, zinc, copper, iron, sulphur, oxygen and carbon for grading
purposes
The purification circuit has the following stages:
Ferric precipitation cascade
Solvent extraction plant for zinc removal
Clean up precipitation cascade
Hydroxide precipitation
Resolution cascade
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Cobalt electrolyte clarification
Ion exchange for nickel removal
a. Ferric precipitation cascade
This is one of the trains at Co purification plant for iron and copper removal from
process liquor solution coming from copper solvent extraction plant and other
recycled streams. It consists of eight mechanically agitated tanks through which
the material gravitates into the thickener (TM1). These tanks include: TK10, TK20,
TK30, TK40, TK50, TK60, TK70 and TK80.
NOTE: TK: Tank, TM: Thickener Module.
De-copperized liquor from Cu-SX plant with composition of Co-5gpl, Cu1500ppm,
Fe-3.5gpl maximum and Zn-100ppm maximum, is pumped to TK10. From TK10,
liquor is pumped to TK20 at 50-60m3/h. Thickener (TM2) underflow also reports to
TK20, which is a mixing tank whose product overflows into TK30. Streams
reporting to TK 40 include: H2SO4 floor sump from Carbon columns and Larox
filtrate and thickener 1 underflow recycle line. At the pH value in the tank of
pH=4.0. Material gravitates to TK50 where H2SO4 is added resulting into pH=3.5.
This overflows into TK60, where both H2SO4 and sodium metabisulphite (Na2S2O5)
are added. Sodium metabisulphite(SMBS) is added in order to reduce the
undissolved Co3+ ions to Co2+ reporting to this train via recycled thickener 2
underflow where Tenke concentrate is fed which bears Co metal in two ionic
forms .i.e. Co2+ and Co3+ ions. In acidic media, Co3+ ions are stubborn and do not
dissolve, hence the need to reduce them to Co2+ ions which are acid soluble. From
TK60, solution overflows into TK70 and finally into TK80. This material finally
gravitates into thickener (TM1).
TM1 is a superstructure-supported thickener for ferric precipitation. To this vessel,
N100 flocculants and Polysilcoagulant are added. Usually Fe precipitate out as
Fe(OH)3 within pH= 2-3. Fe (OH)3 and Fe(OH)2 are slimy and gelatinous materials
where N100 and Polysil are used to settle them. Underflow at pH=4.5, sg=1.15-
1.25, Co<0.08%, collects into TK82 and pumped to either belt or Larox filters for
entrained Co recovery.
WILLIAM C. MIINGA Page xxi
TM1
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
TM1 O/F at a pH=4.0, Fe<2008ppm, suspended solids<100ppm, Cu<2008ppm,
Zn<100ppm and Co>5gpl, it is pumped to Zinc Solvent Extraction Plant for zinc
removal. Consider a simple flow sheet showing material movement at ferric train:
Fe3+ +3OH =Fe (OH)3 ORFe2+ + 2OH=Fe (OH) 2 1.1
Belt/ Larox filtrates Carbon column flow Repulped flowStripped liquor from Cu T/H TM1 recycle line
TM2 underflowH2SO4
SMBS (7-9m3/h) H2SO4
1.25%Polysil N100 (0.889gpl, 0.5-0.6m3/h)
TM1 O/F to Zn SX and Cu T/H
1.25% Polysil
U/F ph=4.5, s.g=1.18-1.2, Co=0.0-0.08% Belt and Larox Filters
Figure 1.2: Flow diagram showing material movement at Ferric Train
i. Sodium Metabisulphite
Sodium metabisulphite(SMBS) or Sodium Pyrosulfic is an inorganic compound of
chemical formula Na2S2O5. It is mostly used as a Disinfector, Antioxidant, and as
Preservative agent. However, at Chambishi Metals Cobalt Plant, SMBS is used for
reducing of Co3+ ions in cobalt concentrates to Co2+. This is because SMBS like
any other sulphite, acts as a reducing agent in aqueous form i.e.
Na2S2O5(aq) = 2Na+(aq) + SO3
-(aq) + SO2 (aq) 1.1c
WILLIAM C. MIINGA Page xxii
TK10
TK40TK50 PH=4
TK60PH 3.8
TK70PH=3-4
TK80PH=3-4
TK82
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
SMBS solution is prepared both at leach and pyrite plants where bags of 25kg of
white SMBS powder are stock pilled. At leach plant, it is used for Camec
concentrate leaching and at purification; it is used for Tenke leaching.
ii. Preparation of Flocculants
Flocculation is a process where colloids come out of suspension in the form of floc
or flakes. The action differs from precipitation in that, prior to flocculation, colloids
are merely suspended in a liquid and not actually dissolved in a solution.
Flocculation refers to the process by which fine particles are caused to clump
together into floc. The floc may then float to the top of the liquid, settle to the
bottom of the liquid, or can be readily be filtered from the liquid. A substance which
causes flocculation is known as a flocculant.
Two types of flocculants used at Chambishi Metals purification includes: N100
Superfloc and E24 Magnafloc. N100 superfloc is used for TM1, TM2 and TM3
thickeners, while E24 is used for TM4 thickener.
E24 Magnafloc Preparation
This is prepared in a tank at the lower terrace of the purification plant. To this tank
of 3m3 volume, 2kg of E24 crystals is added, where spent electrolyte from cobalt
tank house is used as solvent. This is mixed well resulting into an E24 Magnafloc
solution of concentration in the range of 0.667gpl. This is stored in a storage tank
of 7.5m3 volume. From this storage tank, the flocculant solution is pumped to TM4
at a continuous flow rate of about 1-1.12 m3/h.
E24 crystals S/E from Co T/H
WILLIAM C. MIINGA Page xxiii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
1-1.12m3/h to TM4
0.67gpl 0.667gpl
Figure 1.3a: Diagram showing the preparation and movement of E24 solution.
N100 Superfloc Preparation
This is also prepared at the lower terrace of the purification plant in a tank of
volume 4.5m3. To this tank, 4kg of N100 superfloc crystals is added where water is
used as a solvent. This is mixed together resulting into a solution of 0.889gpl
concentration, which flows into an 11m3 storage tank. From this storage tank, N100
flocculant solution is pumped to TM1, TM2 and TM3 at different flow rates of 0.5-
0.6m3/h, 1.6-1.7m3/h and 2.5-2.7m3/h respectively.
N100 crystals water
0.5-0.6m3/h to TM1
0.889gpl
TM2 (1.6-1.7m3/h)
TM3 (2.5-2.7m3/h)
Figure 1.3b: Showing the preparation and movement of E24 solution.
WILLIAM C. MIINGA Page xxiv
Preparation TankV=3m3
Storage Tank
E24 solution
Preparation Tank
V=4.5m3
Storage Tank0.889gplN100 solutionV=11m3
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
iii. Larox Filters
There are two larox filters at Chambishi Metals i.e. Larox 1 and Larox 2. These are
pressure filters known as Filter Presses. They are widely used for treating of
slurries with high solids content e.g. filtering of TM1 U/F
Currently, both Larox 1 and Larox 2 filters treat same TM1 U/F material, unless
when the roaster is in operation, Larox 2 is used for filtering of leached calcine from
roaster. Larox 1 produces gypsum as filtered cake while Larox 2 does not, because
Larox 2 does not have a conveyor. Therefore, Larox 2 produces filtered cake,
which is repulped and pumped to the dam while Larox 1 produces gypsum used in
cement and fertilizer manufacturing industries.
Stages of Larox Operation
Larox filters are operated in stages, which include the following:
Filtration: This is the first stage of Larox operation where slurry with
s.g=1.18-1.20 is fed to the frame. The filtrate passes through the cloth while
cake is retained. After filtration, what follows is:
Pipe and Hose Washing
Pressing 1; Cake Washing
Pressing 2; Pipe Drain
Air Drying
Pressure Release
Plate Pack Opening
Cake Discharge
Plate Pack Closing
WILLIAM C. MIINGA Page xxv
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
b. Solvent extraction for zinc removal
The purpose of the zinc solvent extraction plant is to remove zinc from the process
liquor solution and increase cobalt recovery. To achieve effective zinc control, the
ferric thickener overflow pH should be maintained in the range 3.5-4.5. Pregnant
liquor solution from TM1 (ferric thickener) overflow is pumped through the filter to
remove suspended solids. The filtrate is then pumped to the four mixer-settlers in
series. Zinc extraction is achieved by the use of D2EHPA in a diluents shell sol
3525.
Below is an equation for the extraction of zinc.
ZnSO4 (aq) + 2HR(org) ↔R2Zn(org) + H2SO4(aq) 1.2
Two layers are formed with the top layer being the loaded organic due to its low
density and the bottom layer being the aqueous (raffinate), which is continuously
pumped to the clean-up cascade.
Stripped/scrubbed organic is also fed to four mixer-settlers in a counter current
mode. During extraction zinc is extracted to the organic and the acid is liberated
into the aqueous solution. The loaded organic is then stripped using sulphuric acid.
Zinc is stripped from the loaded organic by mixing it with 150-200gpl H2SO4.
H2SO4 (aq) + R2Zn (org) ↔ 2RH (org) + ZnSO4 (aq) 1.3
The stripped organic is later on scrubbed using 150-180gpl hydrochloric acid. The
raffinate solution rich in cobalt is then pumped to the clean-up cascades for further
processing.
Consider a simple flow sheet showing the movement of liquor in the cells i.e.
WILLIAM C. MIINGA Page xxvi
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
RAFFINATE TO TM2(<10ppm Zn)
32m3/h150-170gpl Zn
H2SO4+water25-30m3/h stripped organic
180gpl
HCl+water
AqueousFeed TM1 O/F
(60-110m3/h)
Figure 1.4: Flow sheet showing liquor movement at Zn SX plant
c. Clean up precipitation cascade
The purpose of the clean-up precipitation cascade is to control zinc in the thickener
O/F at < 4ppm concentration. It consists of five cascading vessels and a thickener.
These include:
TK10: A receiving vessel of almost all feed streams to the clean-up train. These streams include;
Raffinate solution from Zn SX plant
Prepared Tenke cake
Rock lime, to maintain pH within the range of pH= 6.2-6.5
Larox and belt filtrates
Co eluate from Ionex plant
Repulped TM4 U/F from drum filter
TM1 O/F by-passing line via pp64
Recycled TM2 underflow
WILLIAM C. MIINGA Page xxvii
E4PH=2.8
E3PH=2.9
E2PH=3
E1PH=3
POLISHER FILTER
STRIPPING CELL 1
STRIPPING CELL2
SCRUBBING CELL
STRIPPED/SCRUBBED ORGANIC TANK TK90
LOADED ORGANIC TK280
STRIPPED ORGANIC TANK TK340
STRIPPING SOLUTION TANK TK170
SCRUBBING SOLUTION TANKTK160
RAFFINATE TANK TK190
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
TK20: This is a mixing and reaction tank receiving feed from TK10. TK30: Receives feed from TK20. It is a pH control vessel where quicklime is added
sometimes depending on the performance of added rock lime. This is in order to
maintain a pH= 6.5- 6.6. TK40: Feed comes from TK30. It is for pH control where
quicklime is also added. This vessel feeds TK50. TK50: This is basically a reaction
vessel realizes it’s feed into TM2. TM2: To its material, N100 flocculant is added.
Its overflow reports to TK20 of the Hydroxide Train while underflow reports to TK40
of the Ferric Train. Consider a simple flow sheet drawn below showing liquor
movement and some other important parameters:
TM4 U/F & Raffinate from ZnSX PlantTenke Co eluate Belt & Larox FiltratesFloor Sump Rocklime
Rocklime/ Quicklime
Quicklime
N100 Superfloc (1.6-1.7%m3/h)
TM2 O/F to TK20 at Hydroxide train (Co>5gpl)
TM2 U/F to Ferric train (Co=5-1.7%, sg=1.15-1.18
Figure 1.5: Flow sheet showing liquor movement at Clean-up Train
WILLIAM C. MIINGA Page xxviii
TK10 (mixing & control vessel)PH=6.2-6.5
TK20(reaction vessel)
TK30 (pH=6.5-6.6)
TK40 (pH=6.4-6.8)
TK50 (reaction vessel)
TM 2
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
d. Cobalt hydroxide precipitation cascade
The purpose of the hydroxide cascade is to precipitate cobalt and concentrate it by
dewatering. The hydroxide circuit consists of 6 cascading vessels and a thickener.
TK10 receives TM2 o/f and filtrate from drum filters. The liquors are pumped to
TK20 then TK30 where quicklime is added to precipitate cobalt as hydroxide.
TK40, 50 and TK60 are reaction vessels. TK60 discharges into the thickener where
solid/liquid separation takes place with the aid of a flocculant. Caustic soda is
added to increase the pH. The reacted slurry is feed to the thickener for solid/liquid
separation.
Co2+ + OH- =Co(OH)2 1.4
The thickener overflow is disposed off to the tailings dam. The underflow is
pumped to the filter for filtration. The cobalt hydroxide cake is repulped with spent
electrolyte from the cobalt tank house and pumped to the resolution train for further
processing. Consider a simple flow sheet drawn below showing liquor movement
and some other important parameters:
WILLIAM C. MIINGA Page xxix
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
TM2 O/F belt filter filtrates
Quicklime Hydroxide filtrate, floor sump
Quicklime
N100( 2.5-2.7m3/h)
Water to the dams (<100ppm Co)
Co hydroxide (18-20% solids, s.g=1.08-1.15, Co>15%)
Figure 1.6: showing the movement of liquor at hydroxide train
i. HYDROXIDE BELT FILTER
At Chambishi Metals, this is one of the filters used for filtering of TM3 underflow. It
consists of a long horizontal belt where feed is fed and filtered from.
Operations
The belt receives its feed from TM3 U/F via three pumps: pp72, pp89, pp90 at
approximate flow rates of 21-22m3/h, 25-28m3/h and 6-8m3/h respectively. The feed
reports to the belt moving at a speed of 300-357rpm, from which it is filtered from.
Filtered cake at the end of the belt falls into a chute where it is repulped with
recycled hydroxide liquor solution from TK160. This is done in order to easy the
flow of the filtered hydroxide cake in the chute to TK110. From TK110, repulped
WILLIAM C. MIINGA Page xxx
TK10 (receiver)
TK20 (mixing & pH control vessel (7.8-7.9)
TK30 (REACTION VESSEL)
TK40 (Control vessel pH=8.0-8.1)
TK50 (reaction vessel)
TK60 (reaction vessel)
TM3
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
cake is pumped to TK160, where spent electrolyte from carbon columns is fed via
TK89 and TK88 at about 30m3/h. TK160 pumps its material to two vessels, one
reports to the Resolution Train while the other reports back to the belt chute where
it is used for repulping of the filtered cake reporting to TK110.
For belt washing, industrial water used comes from TK150. This used water then
collects into TK140. In the past, TK140 used to pump its recovered water to the
Washate feed zone where solids and Co could be recovered with the filtrate getting
back to TK150 for belt washing. But currently, TK140 pumps its water to hydroxide
train since the Washate zone is no longer in operation. Therefore, water for belt
washing comes from Kafue River into TK150 at a flow rate of 15-25m3/h. Spirages
collects into TK140, then to the Hydroxide train.
ii. HYDROXIDE DRUM FILTERSThere are currently three drum filters used for cobalt hydroxide slurry filtration.
These filters receive their feed from TM3 U/F collecting box via two pumps, pp88
and pp89, at approximate flow rate of 60m3/h. The feed is fed on the drum clothes
via feed panels. Air used for filtration comes from nash vacuum pumps.
During filtration, the collected filtrate is taken back to TM3 via TK20 while the
filtered cake is repulped with spent electrolyte from carbon columns in the chute.
This repuled cake is then pumped to either TK63 or TK64 of the resolution train.
e. Cobalt resolution cascade
Its purpose is to re-dissolve the precipitated cobalt and control zinc. The cobalt
hydroxide from TM3 is filtered and repulped with S/E from electro-winning section
before pumping back to resolution cascade. The train receives repulped hydroxide
cake from the cobalt hydroxide filter and any excess cobalt spent electrolyte.
Sulphuric acid is added to achieve the pH set point. The reacted solution goes for
solid/liquid separation in the thickener. The underflow slurry is pumped to the filters
for filtration. The filtered cake is repulped with water or ferric filtrate and pumped to
the clean-up cascades. The overflow thickener pumped to the clarifier thickener for
clarification. Consider a simple flow sheet below to understand material movement
at resolution train.
WILLIAM C. MIINGA Page xxxi
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
TM3 U/F & Spent Electrolyte H2SO4
H2SO4
E24 (1.0-1.12m3/h, 0.607gpl)
To TM5
Filtrate to TK10
Repulped cake to TM2
Figure 1.7: Showing the movement of liquor at resolution train
f. Cobalt electrolyte clarification
i. CLARIFIER(TM5)
This is the stage of purification where TM4 O/F solution is clarified prior to feeding
the Co tankhouse.
TM4 O/F reports to TM5 at 100-120m3/h Once in TM5, no chemical is added to the
liquor. TM5 reduces total suspended solids (TSS) in solution to <100ppm. This is
achieved through consistent check-up of U/F specific gravity (s.g) which should
always be <1.15. If the sg is >1.15, the thickener is bleed by opening the
underflow. This is done every two hours, 2-3 times per shift. The O/F liquor at a
pH=5-6, reports to two pre-coat feed tanks: A and B or (TK20 and TK50). From
these two tanks, liquor is pumped to Buffalo filter and the three pre-coat filters; A, B
and C. These filters remove total suspended solids to less than 50ppm. Pre-coat
filters consist of plate leaves for solids removing from solution. Plate leaves are
constantly cleaned to maintain their performance efficiency. This is done by
unscrewing them from the filter and washing them with water, or soaking them in
WILLIAM C. MIINGA Page xxxii
TK10 (control vessel) pH=6.2
TK20 (control vessel) pH=6.1
TK30 (reaction vessel)
TK40 (reaction vessel)
Drum filter
TM4 (solid/liquid separation)
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
HCl. From the filters, liquor solution is pumped to carbon feed tanks A and B. From
these two tanks, the solution is pumped to carbon columns for sulphides and
organics removal.
ii. CARBON COLUMNS
Cobalt liquor solution from carbon feed tanks is fed to carbon columns with the
help of solution level measuring devices which are there for liquor level balancing
in the tanks. Carbon columns contain activated carbon granules which remove
both sulphides and organics from solution to < 0.5ppm. From the carbon columns,
process solution is pumped to ion exchange feed tanks which feed liquor to the
Nickel ion exchange plant. However, when sulphides levels in liquor going to ISEP
tend to be >0.5ppm, carbon columns are regenerated. However, back washing is
more often done than regeneration.
Carbon Column Back WashingCarbon granules in columns are restored to their performance efficiency by back
washing. This is done when column cone pressure is 4 bars, and when there is
inadequate feed to the column.
During carbon column back washing, the column is first cut from the line by closing
all lines leading liquor to it. Then a slag of carbon granules is drawn from it into the
regeneration column or back-washing vessel. A slag is the amount of carbon
granules allowed to flow from the column into the regeneration vessel in one
minute. Therefore, during back washing, carbon granules occupying the bottom
cone of the column are made to flow into the back-washing vessel, which is about
1-2 slags. This creates space at the top of the column allowing already back
washed carbon granules in the charge tank to flow into the column.
Once in the regeneration vessel, carbon granules are back washed by passing
water through them from the bottom. This process continuous until the discharge
from the top into the sump is clear water, and it lasts depending on how dirty the
granules were. Back wash discharge collects into the sump and is pumped to TK40
at ferric train. This is done on a daily basis depending on the performance of the
carbon granules as depicted by the operator.
WILLIAM C. MIINGA Page xxxiii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Carbon Regeneration.
This is also done based on the performance efficiency of the carbon granules in
removing of sulphides and organics from Co liquor solution .i.e. when sulphide
levels in solution going for nickel removal at Ion exchange plant exceed 0.5ppm.
During this operation, a carbon column being regenerated is first cut from the line
of the system. But before the column is isolated from the system, a sample is cut
from the liquor passing through the column and pH determined. The column is then
drained-off of all solution and flashed with water until the discharge of water
flashing is with pH=7.
1st Stage: While flashing, hydrochloric acid (HCl) solution is prepared in an acid
tank of volume 18m3. This is done by adding 40% by volume of water to the tank
where 400liters of HCl is added .i.e.
H2O=7.2m3=7200litres
HCl=400litres
Concentration=5.3%HCl solution
Therefore, 5.3%HCl solution is then pumped through the carbon column under
regeneration from the top. This process lasts 4-5 hours, and it helps in removing of
gypsum impurities in the carbon granules.
2nd Stage: When HCl acid pumping is stopped, all valves are closed and water
pumped into the column to flash out HCl from the column. This water collects into
the sump, and pumped to ferric train together with residual HCl in the acid tank.
Then a fresh amount of 40% by volume water is added to the acid tank, where
10kg of 99.7% potassium dichromate (K2Cr2O7) is. To this mixture, 500litres of
sulphuric acid (H2SO4) is also added .i.e.
H2O= 7200litres
Concentration of K2Cr2O7=1.3gpl
Concentration=6.5%H2SO4 solution
This solution is then passed through column for about 4hours. Thereafter, water is
used to flash out acid solution from the carbon column through the bottom.
Samples are cut. When there is >100ppm Co with pH< 2.0, the washing water is
pumped toTK206 at Ni plant, from which it is pumped to thickener 5 at roaster. This
continuous until pH=4, where flashing is stopped and the column put back on line.
Co electrolyte begin to pass through the column and is sent back to purification
WILLIAM C. MIINGA Page xxxiv
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
plant until its pH=4, that is when it is put back on line. Flow rate is increased
depending on the change in the pH of the solution. Consider the diagram below
showing the liquor movementOverflow
From TM4
TO TM4 sg=1.15 TSS<100ppm
TSS<50ppm
FOUR CARBON COLUMNS
Feed to IONEXSulphides<0.5ppmTSS<50ppm
Figure 1.8: Showing the movement of liquor in clarifier/carbon columns
g. Nickel ion exchange
Its objective is to removal the nickel impurity from the cobalt solution in order to produce
cobalt of less than 0.10% nickel.
The plant consists of thirty cells filled with a special resin type, DOW M4195 and
the cells mounted on a large turntable. The cobalt electrolyte stream is passed
WILLIAM C. MIINGA Page xxxv
TM5PRECOAT FEED TANK
PRECOATE FEED TANK
BUFALLO FILTER PRECOATE
FILTERPRECOATE FILTER
PRECOATE FILTER
CARBON COLUMNS FEED TANK A
CARBON COLUMN FEED TANK B
A B C D
IONEX FEED TANK
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
through a number of cells in the adsorption zone where both cobalt and nickel load
onto the resin. In order not to lose cobalt during elution, a split elution is done.
Sulphuric acid at a 10 gpl is passed through the resin to strip most of the cobalt
and a portion of the nickel. This stream is then recycled to TM1. Nickel is then
removed using a more concentrated acid of 100 to 150gpl.
The resin is then backwashed to displace the acid, and the resin returns to the
adsorption zone. During this process, the suspended solids are removed. The
cobalt electrolyte is preheated before being fed to the cobalt tank house. Consider
the diagram below to understand the flow of liquor at IONEX Plant;
Co electrolyte from C-columns
>120m3/h, 50-350ppm Ni
H2SO4(5-10gpl)20-25m3/h
H2SO4 (100-150gpl)
Bleed back to TK60
Back wash effluent to TK206
Co electrolyteTo TK10 at Co T/H
To TK206To TK10 at Clean-up Train
Figure 1.9: Showing the movement of liquor at IONEX.
WILLIAM C. MIINGA Page xxxvi
TK90IX FEED TANK
TK40 Ni Eluant Tank
TK30 Co Eluant TK70 Water Tank
TK20 Acid Tank
ISEP VALVE & CELLS
TK50Co Eluate Tank
TK60Ni Eluate Tank
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
b) Cobalt tank house
Cobalt advance electrolyte from Ion-ex reports to TK10, from which it is passed
through heat exchangers.From TK10 via heat exchangers, Co advance electrolyte
at 120m3/h, Co: Ni=150min, Zn<0.5ppm, TSS<50ppm, Co>20gpl and pH=1.0,
reports to four tank house distribution boxes. These distribution boxes feed the
electrolyte to the cells divided into two sections .i.e. East and West sections. A
section has got 37cells. In each cell, there are 31anodes and 30cathodes. Anode
terminals are made of lead antimony, while cathode ones are made of stainless
steel. Therefore, A/E from the distribution box flows into the cells at a flow rate
dependent on factors such as:
Current
pH
Tenor
Temperature
Cell voltage
Co electrolyte enters the cells as A/E and comes out as S/E (spent electrolyte).
Across these cells, a DC current from two rectifiers is applied on each cathode and
anode. The amount of current across each cell is 13.5KA, with each cathode
carrying approximately 450A. Cell voltage vary from 4.5-7.5V depending on the
material being treated. Anode and cathode plates in a cell are electrically
connected in parallel so that the potential difference across the cell is the same as
the voltage drop between the two terminals. DC current from rectifier flows through
the busbars into the anodes. From the anodes, it passes through the electrolyte
onto the cathode. During this movement, Co metal in electrolyte is electroplated
out of solution onto the cathode terminal. After the days of maturity, cathodes are
removed from the cell and electroplated Co stripped from them.
Two things are common with potential drop across a cell. When it is higher than
that of the cell average, it means that the following conditions might be prevailing
i.e.
Loose, dirty contacts between anode/ cathode hanger bars and knife-edges.
WILLIAM C. MIINGA Page xxxvii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Poorly conducting anodes due to heavy passivation cracks, or loose contact
between the anode and hanger bars.
In case of situation where potential drop is lower than that of the cell average, it is
mostly caused by:
Nodules on the cathodes
Shorts in the cell due to peelers
Cell sludge accumulation
a. Degassing
Cobalt metal is degassed in order to lower its hydrogen gas content. This is done
by heating the metal to temperatures of about 780-820oC in a degassing furnace at
a pressures around 720mmHg in batches of 2.5-5 tons. This forces all the gas
contained in the metal to escape raising the grade of the metal.
b. Burnishing
This is the polishing of the degassed cobalt metal to restore its silver shining
surface. It takes about 30-60minutes to burnish cobalt flakes. After which they are
discharged into 5.0tons capacity hopper prior to filling the shipment drums.
c. Drumming
Cobalt from hoppers is filled into drums, where sampling is done as the drums are
being filled. After being drummed, the metal in the drums is sampled and weighed
besides labeled. Usually, it is packed in drums of 250kg and handled over for
dispatch.
d. Peelers
Peelers refer to cobalt metal that peels off the cathode blanks whilst in cells. They
reduce the current efficiency of the process by causing a lot of shorts in cells nd
they are caused by:
The amount of sulphur in the electrolyte
WILLIAM C. MIINGA Page xxxviii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
The amount of manganese in the electrolyte: high amounts cause Co to be brittle
and forms cracks easily.
Suspended solids
Gelatinedosage also cause peelers i.e. if you over-dose.
Temperature gradient across a cell i.e. if high.
Electrolyte flow rate when low resulting into adherents.
Peelers in Co tankhouse are controlled by operating at optimum conditions.
e. Nodules
Just like peelers, they reduce current efficiency by causing a lot of shorts. They
form during electro-winning and are constantly removed from the electroplated
cobalt to prevent them causing shorts. When enough, they are degassed and
burnished before drumming.
f. Dispatch
This is the stage where Co metal packed drums are now packed in groups of fours
and shipped
g. Anode Pretreatment
This is done in order to regenerate the anodes. It is done by preparing
10%concentrated H2SO4 acid in a tank and adding 20kg of Potassium Dichromate
to the tank to come up with 0.2%solution of Potassium Dichromate. This is agitated
for 10min, and anode plates dipped in the solution for 24hours. Then the anodes
are removed and hagged on the racks ready for use.
h. Cathode Preparation
To avoid the formation of peelers and adherents on the cathodes, they are cleaned
before taken back for use. After stripping Co metal, cathodes are dipped into nitric
acid. After which, they are again dipped into hot water and left to dry outside. After
drying, they are soaked into 7.9g/m3gelatine solution after which, they are left to
dry and ready for use.
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Co electrolyte fromIX
Co>20gpl at >120m3/h, pH=1.0minZn<0.5ppm, TSS<50ppm,
Pretreated anodes, demisting balls
Pulled cathodes
Glued cathodes
Cleaned cathodes
Stripped cathodes
Co sheets 55%Nitric acid
O/S particles recycled
Half Co sheets
U/S particles
Co Export
Figure 2.0: Showing the flow of material at the Cobalt tank House.
WILLIAM C. MIINGA Page xl
TK10
Heat Exchngers
East and West Sections with 74 cells
Wash Tank At 40oC
Glue Dip Tank
Cathode stripping section
Nitric acid Dip tank
Breaking machine
Crushing machine
Degassing at 820oC
BurnishingMetal loaded into drums
Drums sealed, weighed & numbered
TM1(Solid/liquid separation)
Zn SX(Solvent Extraction)
TM2(Solid/liquid separation)
TM3(Solid/liquid separation)
Cobalt recovery plant& waste water disposal
O/F
O/F
U/F
O/F
Larox (Gypsum)
Stripped liquor from Copper Solvent extraction plant
Feed (Tenke)
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
2.2. CURRENT FLOW SHEET AT COBALT PURIFICATION PLANT
TM= thickener number
O/F= thickener overflow
U/F= thickener underflow
Figure 2.1: Current Chambishi Metals Cobalt Plant Flow Sheet
WILLIAM C. MIINGA Page xli
Cu 445 ppm
Zn ≤ 10 ppm
Resolution Stage
U/F
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
CHAPTER THREE
LITERATURE REVIEW
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
3.1. BASIC CONCEPTS OF ION EXCHANGE
Ion exchange is a reversible chemical reaction where an ion (an atom or molecule
that has gained or lost an electron and thus acquired an electric charge) from
solution is exchanged for a similarly charged ion attached to an immobile solid
particle called Ion Exchanger. These solid ion exchange particles are either
naturally occurring inorganic zeolites or synthetically produced organic resins. The
synthetically produced resins are the predominant type used today because their
characteristics can be tailored to specific application. (R.Minango, 1993)
The process occurs with no structure changes in the resin. At some point during
the ion exchange process ion exchange equilibrium is established. The general
reaction for the exchange of ions A and B on a cation exchange resin can be
represented as follows.
nR-A+resin + Bn+
sol n R-nB+
resin + nA+soln………………………………..2.1
Where R is an anionic group attached to the ion exchange resin, and A+ and B+ are
ions in the solution and n is a group valence.
An organic ion exchange resin is composed of high-molecular _ weight
polyelectrolyte that can exchange their mobile ions for ions of similar charge from
the surrounding medium.
Each resin has a distinct number of mobile ions sites that set the maximum
quantity of exchanges per unit of resin. For exchanger, in the case of Copper ions
(Cu2+) in solution, a resin with Hydrogen ions available for exchange will exchange
those for Copper ions in the solution. The reaction can be as follows. (Dowex,
2011)
2(RSO3H) +CuSO4 (RSO3)2Cu + H2SO4………………………………….2.2
RSO3 indicates the organic portion of the resin and H is the immobile portion of the
ion active group.
Two resin sites are needed for the Copper ions with a plus two valence (Cu2+).
Trivalent ferric ions would require three sites. As shown above, the ion exchange
WILLIAM C. MIINGA Page xliii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
reaction is reversible. The degree of the reaction to proceed to the right will depend
on the resins preference or selectivity of a resin for a given ion is measured by the
selectivity coefficient. K which in its simplest form for the reaction
RA+ + B+ RB+ + A ……………………………………………...2.3
Is expressed as K = (concentration of B+ in resin/ concentration of A+ in resin) x
(concentration of A+ in solution/ concentration B+ in solution)
The selectivity coefficient expresses the relative distribution of ion when resin in the
A+ form is replaced in a solution containing B+ ions. Table 2.1 gives the selectivity
of strong acid and strong base ion exchange resins for various ionic compounds.
It should be pointed out that the selectivity coefficient is not constant but varies with
change in solution conditions. It does provide a means of determining what to
expect when various ions are involved. As indicated in Table 2.1, strong acid resins
have a preference for nickel than sodium. Despite this preference, the resin can be
converted back to the hydrogen form by contact with a solution of sulphuric acid
(Eqn 2.4).
(R-SO4)2Cu + H2SO4 2(R-SO3H) + CuSO4 ………………………………2.4
This step is known as regeneration. In general terms, the higher the preference a
resin exhibits for a particular ion, the greater the exchange efficiency in terms of
resin capacity for removal of that ion from the solution. Greater preference for a
particular ion, however, will result in increased consumption of chemicals for the
regeneration. (Dowex, 2011)
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Table 2.1- selectivity of ion exchange resins in order of decreasing preference. (L. Rosato, 1984)
3.2. TYPES OF RESINS
Many different types of resin have been developed namely cation exchangers, anion
exchangers and chelating exchangers.
3.2.1. CATION AND ANION EXCHANGE RESIN
Cation and anion exchange resins have fixed ions known as Co-Ions and mobile
ions of opposite charge called Counter- Ions. The co-ions are bound to an insoluble
microporous matrix, while the counter-ions reversibly interchange with ions in
surrounding solution. Anion exchangers are resins that have fixed positive ion
(cations) on the framework and so can exchange negative ions (anions) from a
solution. Cation exchangers are resins that have fixed negative ions (anions) on the
framework and can exchange positive ions (cations) from a solution, as depicted in
Figure 2.1. It should be noted that in any ion exchange reaction each separate phase
(solution and resin) within the system would maintain its overall electro neutrality.
Figure 2.2 Schematic sections through a cation exchange resin. (R.Minango, 1993)
WILLIAM C. MIINGA Page xlv
Strong Acid Cation
Exchange
Strong Base Anion Exchange
Barium IodideLead Nitrate
Calcium BisulfateNickel Chloride
Cadmium CyanideCopper Bicarbonate
Zinc HydroxideMagnesium FluoridePotassium Sulfate
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
From Figure 2.1 it can easily be understood that the SO3⁻ions, which are usually
the fixed ions in cation resins, are fixed to the resin framework, while the H+ ions
are free to move throughout the structure. As a result, sodium ions can enter the
resin freely, causing the rejection of hydrogen ions, whereas chloride ions (Cl⁻)
approaching the surface of the resin are repelled by the fixed negative charges
(SO3⁻) and cannot enterbecause it is a cation resin. Note that when a resin has H +
as its free ions, it is said to be in H+ form. If Na+ are the free ions, then it is in the
Na+ form etc.
The anion and cation are produced from the same organic polymers. They differ
from the ionizable group attached to the hydrocarbon network. It is this functional
group that determines the chemical behavior of the resin. Resins can be broadly
classified as strong or weak exchangers.
Most ion exchanger resins in use today are synthetic materials made up of a
polymer matrix (generally chains held together by divinyl Benzene crosslink) with
soluble ionic functional groups attached to the polymer chains. The total number
and kind of functional groups in a resin determine the exchange capacity and the
ion selectivity while the polymer matrix provides insolubility and toughness to the
resin. (benefied, 1982)
Ion exchange resins are usually classified in the following manner:
1. Cation exchange resin (contains exchangeable cations):
a) Strong-acid exchange resins (SAC)
b) Weak-acid exchange resins (WAC)
2. Anion exchange resins (contain exchangeable anion):
a) Strong – base exchange resins (SBA)
b) Weak – base exchange resin (WBA)
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
A. STRONG ACID EXCHANGE RESINS
Strong acid cation exchangers are so named because their chemical behavior is
similar to that of a strong acid. These resins contain function groups derived from
a strong acid (normally sulphuric acid). The resins are highly ionizable in both the
acid (R-SO3H) and salt (R-SO4Na) form. They convert a metal salt to the
corresponding acid by the reaction:
2(R-SO3H) + Na(R-SO4) Na(R-SO3) + H2SO4……………………….2.5
The hydrogen and sodium form of the strong acid resins are highly dissociated
and the exchangeable Na+ and H+ are readily available for exchange over the
entire pH range.
B. WEAK ACID EXCHANGE RESIN
In a weak acid resin, the ionizable acid group is a carboxylic group (COOH) as
opposed to sulfonic acid group (SO3H) used in strong acid resin. Such resins are
useful only within a fairly narrow pH range. Weak acid resins exhibits a much
higher affinity for hydrogen ions than do strong acid resins.
This characteristic allow for regeneration to hydrogen with significantly less acid
than is required for strong acid resins. The degree of dissociated of a weak acid
resin is strongly influenced by the solution pH. A typical weak acid resin has limited
capacity below a pH of 6.0. (Dowex, 2011)
C. STRONG BASE ANION EXCHANGE RESINS
Strong base anions are highly ionized and can be used over the entire pH range.
These resins are used in the hydroxide (OH) for water deionization. They will react
with anions in a solution and can convert an acid solution to pure water.
R-NH3OH + HCL R-NH3CL + HOH…………………….2.6
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Regeneration with concentrated sodium hydroxide (NaOH) converts the exhausted
resin to the hydroxide form and the regeneration efficiency of these resins is 30 to
50%.
D. WEAK BASE EXCHANGE RESINS
Weak base resins are like weak acid resins, in that the degree of deionization is
strongly influenced by pH. Consequently, weak base resin exhibit minimum
exchange capacity above a pH of 7.0. These resins merely sorb acids: they cannot
split neutral salts but they can remove strong acids by adsorption. (Dowex, 2011)
Figure 2.3 Discharge capacity vs pH profile for weak acid and weak base resin types. (R.Minango, 1993)
3.2.2. HEAVY – METAL – SELECTIVE CHELATING RESINS
Heavy – Metal – Selective chelating resin behave similarly to weak acid cation
resins but exhibits a high degree of selectivity for heavy metal cations. A chelating
resins exhibits greater selectivity for heavy metals in its sodium form than its
hydrogen form. Regeneration properties are similar to those of weak acid resin; the
chelating resin can be converted to the hydrogen form with slightly than
stoichiometric doses of acid because of the fortunate tendency of the heavy metal
complex to become less stable under low pH conditions. (L. Rosato, 1984)
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
3.2.3. LEWATIT VP OC 1026 RESINS
LEWATIT VP OC 1026 is a cross-linked polystyrene based macro porous resin
which contains Di-2-ethylhexyl-phosphate (D2EHPA). This active ingredient is
directly incorporated during the formation of the copolymer and is fixed by
adsorption. This gives a resin of very good matrix and compared with impregnated
resins a relatively high concentration of active ingredient; in addition, loss of
extraction during operation is minimized (as long as the pH of the process solution
as well as rinse water is kept below pH 4). (lanxess, 2011)
A. AFFINITY ORDER FOR TYPICAL CATIONS
Cations are adsorbed by LEWATIT VP OC 1026 in the following order of affinity
which varies as a function of solution pH:
Ti4+ > Fe3+ > In3+ >Sn2+ > Bi3+ > Vo2+ > Be2+ > Al3+ > Zn2+ > Pb2+ > Ca2+ >
Mn2+ > Cu2+ > Fe2+ > Co2+ > Ni2+ > Mg2+ > Cr3+ >>>>>Alkali
(lanxess, 2011)
3.3. TECHNOLOGY / EQUIPMENT DESCRIPTION
The initial part of this section describes some of the more important design
elements of ion exchange systems and the letter part presents a description of
commercially available equipment.
3.3.1. BATCH AND COLUMN EXCHANGE SYSTEMS
Ion exchange processing can be accomplished by either a batch method or a
column method. In the first method, the resin and solution are mixed in a batch
tank the exchange is allowed to come to equilibrium, and the resin is separated
from the solution. The degree to which the exchange takes place is limited by the
preference the resin exhibits for the ion in solution. Consequently, the use of the
resin exchange capacity will be limited unless the selectivity for the ion in solution
is greater than for the exchangeable ion attached to the resin. (Dowex, 2011)
WILLIAM C. MIINGA Page xlix
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Because batch regeneration of the solution is inefficient, batch processing by ion
exchange has limited potential for application. Passing a solution through a column
containing a bed of exchange resin is analogous to treating the solution in an
infinite series of batch tanks.
3.3.2. ION EXCHANGE RESINS AND COLUMNS
A wide range of ion exchange resins are manufactured, the choice of which
depends mainly on the type of metal being recovered and the chemical
composition and characteristics of the solution being treated. Properly matching
the ion exchange resin and the process chemistry should result in efficient
operation, quality byproducts and lower operating costs. Inappropriate selection of
the resin can result in total system failure.
Many specialty resins, such as chelacting resins, are also in commercial use.
Chelating resins that exhibits a high selectivity for heavy metal actions over other
cations in solution have been commonly used in metal finishing, especially in the
past ten years. Because of their selectivity, they are especially useful for end of-
pipe polishing following hydroxide precipitation. Chelating resins are also used in
recovery with electroless copper and electroless nickel plating solution. Generally,
chelating resins cannot be used at low pH (<4) and pH adjustment step is typically
needed before the ion exchange process. (Dowex, 2011)
3.3.3. FIXED – BED COLUMN SYSTEMS
Most industrial application of ion exchange used fixed – bed column systems, the
basic component of which is the ion exchange column. The column must;
Contain and support the ion exchange resin.
Uniformly distribute the service and regeneration flow through the resin bed.
Provide space to fluidize the resin during backwash.
Include the piping, valves, and instruments needed to regulate flow of feed,
reentrant, and backwash solutions.
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After the solution is processed to the extent that the resin becomes exhausted and
cannot accomplish any further ion exchange, the resin must be regenerated. Resin
capacity is usually expressed in terms of equivalents per liter of resin. An
equivalent is the molecular weight in grams of the compound divided by its
electrical charge or valence.
The hydraulic loading of resins will vary considerably form application, depending
on: Column design; type of resin employed; concentration of metal in solution;
other characteristics of the feed solution (e.g., pH) and the allowable concentration
of metal in the column effluent. Typical hydraulic loadings range from 2 to 3 gpl of
rinse water per cubic foot of resin. (R.Minango, 1993)
3.3.4. INTEGRATED AGAINST MODULAR DESIGNS
An integrated ion exchange system design is one in which the various components
needed to perform the ion exchange recovery and regeneration functions are
connected within the one unity. Such systems may also have attached electro
wining units and /or chemical treatment system processing the re-generant.
The modular or point source design separates the ion exchange column from the
regeneration and re-generant processing equipment. With the modular design, the
columns are transported to a central station for regeneration (in some cases the
modules are hard piped) the regeneration station can be either in the plating shop
or at an off-site location (i.e. centralized waste treatment facility).
The modular ion exchange strategy can reduce capital costs for small to medium-
sized application where low to moderation frequency is required. Also the modular
units are considerably smaller and therefore do not occupy as much production
area floor space as integrated units (i.e, if the regeneration station is remotely
located to a non-production area. However, operating costs are usually higher for
modular system due to station (or changing operating modes and valve positions
for had piped modular systems) and initiating regeneration.
Some commercial ion exchange modules have the appearance of large cans and
are referred to as ion exchange canisters. With this type of unit, the canisters can
be stacked upon one another to combine anion ant cation types or to increase the
resin bed volume. Standard column designs are also available. (R.Minango, 1993)
WILLIAM C. MIINGA Page li
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
3.3.5. SINGLE Vs DUPLEX COLUMN OPERATION
Duplex column ion exchange systems are used in many chemical recovery
operations especially where a continuous feed flow is expected. Dual column
configuration avoids downtime during regeneration. Two different duplex column
arrangements are commonly used. In one arrangement, which is referred to as
parallel / standby, the feed stream flows through either one column or the other, but
never both.
The off-line column is regeneration and then is held in reverse until the other
column is ready for regeneration. This is a somewhat inefficient use of the two
columns since column switching must take place before breakdown occurs, which
happens before the resin is completely loaded with ions of interest. In the second
case, which is referred to as lead / lag, the two columns are placed in series flow.
During operation, the majority of metal removal is accomplished in the first column
(lead column) until it approaches capacity.
The process can continue until the first column is essentially loaded to full
capacity with ions of interest, since the second column (lag column) will remove
the breakthrough of the first column. After breakthrough is reached, the first
column is taken off-line for regeneration. The switching of the two columns,
initiating of regeneration and other functions of modern ion exchange equipment
is usually controlled by a microprocessor. (Levenspiel, 1972)
3.3.6. COUNTER FLOW Vs COCURRENT FLOW / REGENERATION
One method of categorizing the operation of different ion exchange system is by
the direction of the service flow (i.e. rinse water) Vs the direction of the
regeneration flow, with concurrent operation, the service flow and the regeneration
cycle flow in the same direction and with counter flow, they flow in opposite
direction (service flow can be either downward or upward). Counter current flow is
considered by most sources to be the more efficient method. (Levenspiel, 1972)
With concurrent flow the hydrogen ions metal ions from the top to the lower portion
of the bed. Complex removal of these ions can only be accomplished by the use of
excessive levels of acid regerant. With normal regenerant usage, there is a “heel”
WILLIAM C. MIINGA Page lii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
left at the exit end of the column (i.e. undisplaced metal ions). On the following
service cycle, the desired exchange reaction occurs in the upper position of the
bed. However, as the hydrogen ion concentration increases
towards the lower section of the bed, some exchange with .previously undisplaced
metal ions to metal ion “leakage”.
After regeneration of the counter flow system, the residual ions are in the top of the
bed, with the bottom being fully converted to hydrogen. Thus, there are no residual
metal ions present at the bottom of the bed to permit the leakage reaction to occur
on the subsequent service cycle.
In addition to reduced ion leakage, counter flow regeneration can increase
operating capacities, decrease the need for waste stream pH adjustment and
reduced waster rinsing requirement.
3.3.7. OTHER EQUIPMENT / DESIGN CONSIDERATION
In addition to the basic ion exchange column, auxiliary equipment is employed for
various purposes, among which include: resin bed channeling and fouling
prevention; pH adjustment of the feed stream; solution pump and flow control;
need for regeneration identification; and regeneration cycle co
Pretreatment of the feed stream is usually performed. Filtration is the basic
requirement for nearly all ion exchange applications. If solids are permitted to enter
the ion exchange bed, they will often create an uneven film on the top of the bed
that acts as a plug. The solids will impede flow and cause channeling through the
bed. Channeling of the feed stream solution will result in incomplete usage of the
bed and inefficient processing. Most commonly, cartridge filtration is used for this
purpose. (Levenspiel, 1972)
Multimedia filters are sometimes used in high flow applications, where changing of
the cartridge filters would be too time consuming. Other types of pretreatment
include pH adjustment and carbon filtration. The adjustment of pH is used for
certain applications where resin capacity can be enhanced by increasing or
lowering the pH. Carbon filtration is used to remove certain organics such as oils
WILLIAM C. MIINGA Page liii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
that become irreversible sorbed by the ion exchange resins and oxidants such as
peroxide that can oxidize and ruin the resin.
The means for identifying the point at which regeneration should be initiated varies
among commercially available equipment. The method employed depend on the
overall design of the system (e.g. a lead / lag unit may be able to tolerate some ion
leakage from the first column. (Levenspiel, 1972)
3.3.8. REGENERATION PROCEDURE
After the feed solution is processed to the extent that the resin becomes exhausted
and cannot accomplish any further ion exchange, the resin must be regenerated.
Regeneration displaces ions during the service run and returns the resin to its
initial exchange capacity or to any desired level, depending on the amount of
regenerant used. In general, mineral acids are used to regenerate anions resins. In
normal column operation, regeneration employs the following basic steps:
1. The column is backwashed to remove suspended solids collected by the bed
during service cycle and to eliminate channels that have formed during this
cycle. The backwash flow fluidizes the bed, releases trapped particles and
reorients the resin particles according to size.
During backwash the larger, denser particles will accumulate at the base and
the particle size will decrease moving up the column. This distribution yields a
good hydraulic flow pattern and resistance to fouling by suspended solids.
2. The resin bed is brought into contact with the regenerant solution. In the case of the cation resin, acid elutes the collected ions and converts the bed to the hydrogen form. A slow water rinse then removes any residual acid.
3. The bed is brought into contact with a copper/cobalt solution and other traces of metal ions to convert the resin to the sodium form. Again, a slow rinse is used to remove residual acid. The slow rinse pushes the last of the regenerant through the column.
4. The resin bed is subjected the fast rinse that removes the last traces of the
regenerant solution and ensures good flow characteristics.
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
5. The column is returned to service. (Dowex, 2011)
3.3.9. THE MASS TRANSFER ZONE (MTZ)
The mass transfer zone is defined as the section of the bed over which there exists
a concentration gradient, based on a percentage breakthrough (i.e. Zn in / Znout).
The selectivity of the resin for Zinc over Cobalt is also used to effect the split
elution, whereby an eluant of low acid strength is first used to strip the Cobalt,
which is recycled to the purification circuit as the value species, while the Zinc
remains loaded on the resin.
A higher acid strength eluant is subsequently passed through the bed to strip the
Zinc as the waste stream. The effectiveness of the split elution technique is
measured primarily by the amount of Cobalt lost to Zinc eluant waste stream and
the amount of Zinc recycled into the process.
The principle design issues are:
To maximize Zinc loading on the resin, while minimizing Cobalt loading: and
To optimize the split elution, so as to minimize the amount of Zinc in Cobalt
recycle stream and the amount of Cobalt in the Zinc waste stream. (Jeffers,
1985)
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
CHAPTER FOUR
APPARATUS AND METHODOLOGY
4.0. APPARATUS AND EXPERIMENTAL PROCEDURES
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4.1. APPARATUS AND REAGENTS USED
The following are the apparatus and reagents that were used in the laboratory
for carrying out the experiment;
Vacuum pump pH meter clamp stand 130ml laboratory column 200 liters x 2 empty containers Stop watch Beakers (2x4000ml, 2000ml, 450ml, 50ml) Sample bottles 50ml Stirring mechanism Demineralized water and Concentrated sulphuric acid Tubes Different types of graduated measuring cylinders, 10ml, 100ml, Inert resins Sand
4.2. SAMPLES
TM 2 Overflow
Zinc raffinate
Lewatit vp oc 1026 resins
4.3. EXPERIMENTAL PROCEDURES
4.3.1. LOADING
Column test works were done to determine the breakthrough profile of the metal of
interest. Considering the laboratory column (130ml) which was used for test works,
120ml (bed volume) of resins were carefully added to a dry 130ml laboratory column
using a spatula. To avoid the resin from floating to the surface of the solution the
column was equipped with adequate distribution screen at the column’s head.
Lewatit VP OC 1026 has a relatively high percentage of fine beads. Therefore, inert
resins were used to protect the head screen distributors against plugging. To the
bottom screen distributor a layer of sand was added.
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TM2 overflow solution had a pH of 4.5. Lewatit VP OC 1026 operating pH range is 1-
4. Therefore, TM2 overflow solution’s pH was adjusted to pH 3.5 and 2.5 respectively
by adding ZnSX raffinate in the 200L container and then mixing the two solutions
using a stirring mechanism. The apparatus were set-up and water was passed
through the resins with the help of the of tubes and vacuum pump from the beakers
so as to set the flow rate of the pump to 10BV/h i.e. (120ml/BV x 10BV/h) x
1hr/60min=20ml/min.
The column was charged at this flow rate with TM2 overflow solution from a 200L
container cutting timed samples with the help of a stop watch every 1hour but only
taking the 5th sample for analysis of Co, Cu, Zn, Fe, Mn, and Mg. and The barren
solution (Zinc free) was collected from the bottom of the column into another 200L
container. After 4 days the resins were exhausted and a breakthrough curve was
generated.
4.3.2. ELUTION
Loaded cobalt was selectively eluted with a weaker sulphuric acidic solution,
followed by more concentrated acid solution to strip zinc i.e. a two stage Elution
process was considered
1. 0.5% H2SO4----5BV@5BV/h
2. 5%H2SO4----1BV@5BV/h
Elution was done by passing weak-acid concentrations: 9.4g/l H2SO4. At this
stage only cobalt was expected to come out as cobalt eluate.
After cobalt elution, then 93.9g/l H2SO4 was passed through the resin, so that at
this stage, copper, zinc, manganese, magnesium and iron could come out
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
CHAPTER FIVE
RESULTS AND DISCUSSIONS
5.1. 1st CYCLE
A. LOADING
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Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
During loading, the feed pH dropped from the initial 3.3 at ambient temperature to
a pH value of about 2, after which it started rising at the slower rate until saturation
was reached1. The loading of zinc on the resin was efficient as breakthrough took
place only after 1500 minutes i.e. after 7.2 liters of feed solution has been passed
through the resins.
0 200 400 600 800 1000 1200 1400 1600 1800 20000
50
100
150
200
250
300
350
400
450
0
1
2
3
4
5
6
7
8
9LOADING
Cu ppm Co gpl Zn ppm Fe ppm
TIME(min)
Cu p
pm
Zn ppmCo gpl
Fe ppm
Figure 4.1: Loading profile for Co, Cu, Zn and Fe at 10BV/hr. at ambient temperature
Figure 4.1 shows the breakthrough curves of zinc and cobalt. The zinc
breakthrough was achieved in1500 minutes. The Zinc and Cobalt in the feed were
3.57ppm and 8.563g/l respectively. Lewatit vp oc 1026 was loading very fast in the
first 600 minutes2. And for the first 1300minutes the resins did not stop loading
zinc.
The Zinc in the resultant solution;
1 The drop in PH was because of the ion exchange between zn2+ from solution and H+ in the resins i.e. the process increased the concentration of H+ in solution, hence increasing the concentration of acid in the cobalt leach solution.2 The loading of zinc (or ions) was fast in the first 600minutes because the resins had well-defined number of exchangeable sites (mobile ion sites). Hence, the zinc was adsorbed on the resins reducing the concentration on Zn2+ thus the drop in the Zn graph. As the process continued these sites were depleted i.e. the ion exchange equilibrium was established. Explanation for rise in the graph.
WILLIAM C. MIINGA Page lx
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
The advance coming out from the column had Zinc in the range <0.1ppm –
2.43ppm; this was against 3.57ppm Zinc in the feed solution passing
through the resin.
The advance coming out from the column had Cobalt in the range 7.573gpl –
8.162gpl; this was against 8.563 gpl Cobalt in the feed solution passing
through the resin. The resin was saturated with Cobalt in just 1500 minutes.
B. 1st ELUTION USING 9.4 gpl
0 10 20 30 40 50 60 700
20406080
100120140160
0
0.5
1
1.5
2
2.5
COBALT ELUTION
Zn ppm Co gpl Fe ppm Cu gplTIME (MIN)
Zn p
pm
Co gpl,Cu gpl,Fe PPM
Figure 4.2: Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr. at ambient temperature
Figure 4.2: Shows that the resin lewatit vp oc 1026 was rejecting Cobalt
significantly. Cobalt was being rejected very fast in the first 25 minutes and then
after the rate of rejection became constant. The elution was done for 60 minutes to
recover all the cobalt that had been loaded on the resin.
The Zinc in the resultant solution;
Cobalt eluate coming out during the 1st stage elution process had Zinc in
the range <0.1ppm-146ppm. At this stage, the ideal situation was to have
minor amounts of Zinc in the Cobalt eluate because this is a recovery
stream for cobalt.
WILLIAM C. MIINGA Page lxi
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
C. 2nd ELUTION USING 93.9 gpl H2SO4
0 2 4 6 8 10 12 140
20
40
60
80
100
120
140
160
180
0
5
10
15
20
25
30
35
40
45ZINC ELUTION
Co ppm Fe ppm Cu ppm Zn ppmTIME(MIN)
Co ppmFe ppm Zn ppm
Cu ppm
Figure 4.3 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr. at ambient temperature
Figure 4.3Shows how the loaded Cu, Fe, Co, and Zn on resin were coming out.
The Zinc in the resultant solution;
The Zinc eluate coming out from the column had Copper zinc and iron in the
range of 9ppm to 6ppm, 0.8ppm to 40ppm and 0.5ppm to 171ppm
respectively. The drop in the graphs shows the elution of these impurities
which were loaded on the resin. At this stage, the ideal situation was to elute
more Zinc in the zinc eluate because this stream is not recycled in the plant.
The Zinc eluate coming out from the column had cobalt in the range of
2ppm to 60ppm this is against 2ppm to 1.508 gpl in the cobalt elution. This
is a good recovery.
WILLIAM C. MIINGA Page lxii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
5.1.1. FIRST CYCLE SPLIT EFFICIENCY
1st ELUTION
Table 4.1 Percentage split of Co, Cu, Zn and Fe in cobalt eluate using 9.4 gpl H2SO4 at 5BV/hr.
Time(min
)
Cumulative ,grams % in Co eluate
Co Cu Zn Fe Co Cu Zn Fe
10 0.15080.2131
00.0146
00.000117
099.2
99.9
94.8 3.3
20 0.15500.2168
00.0151
00.000178
098.8
99.8
93.9 2.7
30 0.15690.2180
00.0153
00.000238
098.7
99.8
93.0 2.7
40 0.15760.2185
00.0153
10.000297
098.6
99.7
92.8 2.8
50 0.15790.2188
00.0153
20.000350
098.6
99.6
92.6 2.8
60 0.15810.2190
00.0153
30.000391
098.6
99.6
92.6 3.1
2ND ELUTION
Table 4.2 Percentage split of Co, Cu, Zn and Fe in Zinc eluate using 93.9 gpl H2SO4 at 5BV/hr.
Time(min
)
Cumulative ,grams % in Zn eluate
Co Cu Zn Fe Co Cu Zn Fe
2 0.0012 0.0002 0.000800.0034
2 0.8 0.1 5.2 96.7
4 0.0019 0.0004 0.000980.0064
2 1.2 0.2 6.1 97.3
6 0.0021 0.0005 0.001150.0087
0 1.3 0.2 7.0 97.3
8 0.0022 0.0007 0.001190.0104
0 1.4 0.3 7.2 97.2
10 0.0022 0.0008 0.001220.0120
6 1.4 0.4 7.4 97.2
12 0.00230.0009
60.00123
20.0120
7 1.4 0.4 7.4 96.9
WILLIAM C. MIINGA Page lxiii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
For the Copper, Zinc, iron and Cobalt that was loaded on the resin, an average of
99.7 % Cu and 93.3 % Zn, 98.8 % Co and 2.9% Fe went to the Cobalt eluate.This is
not suitable for a stream that is recycled back into the plant and 0.3 % Cu, 6.7 %
Zn, 1.2% Co and 97.1% Fe went to the zinc eluate. Here the efficiency was very
poor.
5.2. 2ND CYCLE
A. LOADING
0 200 400 600 800 1000 1200 1400 1600 1800 20000
50
100
150
200
250
300
350
400
450
0
1
2
3
4
5
6
7
8
9
LOADING
Cu ppm Co gpl Zn ppm Fe ppm
TIME (MIN)
Cu ppm
Co gplZn ppm,Fe ppm
Figure 4.4 Loading profile for Co, Cu, Zn and Fe at 10BV/hr. at ambient temperature
Figure 4.4 shows the breakthrough curves of cobalt and zinc. The Zn
breakthrough was achieved in just 1800 minutes. The Zinc and Cobalt in the feed
were 3.57ppm and 8.563g/l respectively. Lewatit vp oc 1026 was loading very fast
in the first 900 minutes. And for the first 1500 minutes the resin did not stop
loading zinc.3
The Zinc in the resultant solution;
3 Because of the availability of the mobile ion sites in the resins
WILLIAM C. MIINGA Page lxiv
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
The advance coming out from the column had Zinc in the range 1.76ppm –
3.16ppm; this was against 3.57 ppm Zinc in the feed solution passing
through the resin.
The advance coming out from the column had Cobalt in the range 7.491gpl –
8.162gpl; this was against 8.563gpl Cobalt in the feed solution passing
through the resin. The resin was saturated with Cobalt in just 1800 minutes.
B. 1st ELUTION USING 9.4 gpl
0 10 20 30 40 50 60 700
20
40
60
80
100
120
0
0.2
0.4
0.6
0.8
1
1.2
1.4
Cobalt Elution
Cu ppm Zn ppm Co gpl Fe ppm
TIME (Min)
CU PPMZN PPM
Co gplFe PPM
Figure 4.5 Cobalt elution profile using 9.4gpl H2SO4 at 5BV/hr. at ambient temperature
Figure 4.5: shows that the resin lewatit vpoc 1026 was rejecting Cobalt
significantly. Cobalt was being rejected very fast in the first 40 minutes and then
after the rate of rejection became constant. The elution was done for 60 minutes to
recover all the cobalt that had been loaded on the resin.
The Zinc in the resultant solution;
The Cobalt eluate coming out during 1st stage elution had a higher
concentration of Zinc making the good cobalt eluate poor. At this stage, the
WILLIAM C. MIINGA Page lxv
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
ideal situation was to have less Zinc in the Cobalt eluate because this
stream is recycled in the plant.
C. 2nd ELUTION USING 93.9 gpl H2SO4
0 2 4 6 8 10 12 140
10
20
30
40
50
60
70
80
0
2
4
6
8
10
12
14
ZINC ELUTION WITH 93.9 gpl
Co gpl Fe ppm Cu ppm Zn ppm
TIME(MIN)
Co ppmFe ppm
Cu ppmZn ppm
Figure 4.6 Zinc elution profile using 93.9 gpl H2SO4 at 5BV/hr. at ambient temperature
Figure 4.6 shows how the loaded Cu, Fe, Co, and Zn on the resin were coming
out.
Zinc in the resultant solution;
The Zinc eluate coming out from the column had Copper, zinc and iron in
the range of 01ppm to 13ppm, 1.35ppm to 12ppm and <0.1ppm to 35ppm
respectively. The drop in the graphs shows the elution of these impurities
WILLIAM C. MIINGA Page lxvi
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
which were loaded on the resin. At this stage, the ideal situation was to elute
more Zinc in the zinc eluate because this stream is not recycled in the plant.
The Zinc eluate coming out from the column had cobalt in the range of
07ppm to 70ppm this is against 56ppm to 1.305 gpl in the cobalt elution.
This is a good recovery.
5.2.1. SECOND CYCLE SPLIT EFFICIENCY
1st ELUTION
Table 4.3 Percentage split (2nd cycle) of Co, Cu, Zn and Fe in Cobalt eluate using 9.4 gpl H2SO4at 5BV/hr?
Time(min)
Cumulative ,grams % Co eluate
Co Cu Zn Fe Co Cu Zn Fe
10 0.13050.01060
0.00260
0.00001
98.9
97.6
91.5 1.4
20 0.19040.01340
0.00500
0.00002
98.6
96.8
93.3 1.4
30 0.22120.01590
0.00720
0.00003
98.3
96.5
94.0 1.5
40 0.23570.01820
0.00920
0.00004
98.2
96.6
94.6 1.5
50 0.24340.01970
0.01080
0.00005
98.1
96.8
95.0 1.9
60 0.24900.02070 0.01170
0.00006
98.1
96.8
95.2 2.2
2nd ELUTION
Table 4.4 Percentage split (2nd cycle) of Co, Cu, Zn and Fe in Zinc eluate using 93.9 gpl H2SO4 at
5BV/hr.
Time(min)
Cumulative ,grams % Zneluate
WILLIAM C. MIINGA Page lxvii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Co Cu Zn Fe Co Cu Zn Fe
20.0014 0.0003 0.00024
0.00070 1.1 2.4 8.5
98.6
40.0027 0.0004 0.00036
0.00138 1.4 3.2 6.7
98.6
60.0039 0.0006 0.00046
0.00202 1.7 3.5 6.0
98.5
80.0044 0.0006 0.00053
0.00262 1.8 3.4 5.4
98.5
100.0047 0.0007 0.00056
0.00262 1.9 3.2 5.0
98.1
120.0048
0.00068
0.000591
0.00262 1.9 3.2 4.8
97.8
For the Copper, Zinc, iron and Cobalt that was loaded on the resin, an average of
96.8 % Cu and 93.9 % Zn, 98.4 % Co and 1.6% Fe went to the Cobalt eluate, which
is not suitable for a stream that is recycled back in the plant, and 3.2 % Cu, 6.1 %
Zn, 1.6% Co and 98.4% Fe went to the Zinc eluate. Here the efficiency was also
very poor.
WILLIAM C. MIINGA Page lxviii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
5.3. 3RD CYCLE
A. LOADING
This is an optimized cycle. The pH of the feed solution was reduced from 3.3 to 2.5
and flow rate was reduced to 7.5BV/hr.
Thus from the results obtained it seems that a decrease in flow rate from 10BV/hr.
to 7.5BV/hr. and pH marginally enhances zinc loading. During loading, the feed pH
dropped from the initial pH=2.5 at ambient temperature to a pH value of about
pH=1.6. this is because of the addition of the H+ ions in the process solution at the
loading stage, below is the equation summarizing this statement;
CoSO4.Zn2++ (RO)2PO2H = (RO)2PO2.Zn2+ + CoSO4.H+
(RO)2PO2H represents D2EHPA (Di-2-ethyl-hexyl phosphoric acid)
The loading of zinc on the resins was efficient while cobalt loading on the resins
under these conditions was reduced from 1.316 gpl from the first two cycles to
0.588 gpl.
0 200 400 600 800 1000 1200 1400 1600 1800 20000
1
2
3
4
5
6
7
8
9
10
0
50
100
150
200
250
300
350
400
450
loading
Co gpl Zn ppm Fe ppm Cu ppm
TIME(MIN)
Co gplZn ppmFe ppm
Cu ppm
Figure 4.7 Loading profile for Co, Cu, Zn and Fe at 7.5BV/hr. at ambient temperature
WILLIAM C. MIINGA Page lxix
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Figure 4.7 shows the breakthrough curves of cobalt, copper, zinc and iron. The Zn
breakthrough was achieved in just 1500 minutes. The Copper, Zinc, Iron and
Cobalt in the feed were 381 ppm, 3.57ppm, 2ppm and 8.563g/l respectively.
Lewatit vpoc 1026 was loading very fast in the first 600 minutes. And for the first
1500 minute the resin did not stop loading copper and zinc.
The Zinc/Cobalt in the resultant solution;
The advance coming out from the column had Zinc in the range 0.85ppm –
2.3ppm; this was against 3.57ppm Zinc in the feed solution passing
through the resin.
The advance coming out from the column had Cobalt in the range 8.013gpl – 8.51gpl; this was against 8.563gpl Cobalt in the feed solution passing through the resin. The resin was saturated with Cobalt in just 1800 minutes.
B. 1st ELUTION USING 5.6 gpl
0 10 20 30 40 50 60 700
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0
1
2
3
4
5
6
7
8
9
3rd cycle Elution-1
Co gpl Zn ppm Fe ppm Cu ppm
TIME(MIN)
Fe ppmZn ppmCo gpl
Cu ppm
Figure 4.7 Cobalt elution profile using 5.6 gpl H2SO4 at 5BV/hr. at ambient temperature
Figure 4.7 show that the resin lewatit VP OC 1026 was rejecting Cobalt
significantly. Cobalt was being rejected very fast in the first 40 minutes. The elution
WILLIAM C. MIINGA Page lxx
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
was done for 60 minutes to recover all the cobalt that had been loaded on the
resin.
The Copper and Zinc in the resultant solution;
The Cobalt eluate coming out during 1st stage elution had a higher
concentration of cobalt as it should be. At this stage, the ideal situation was
to have less Zinc in the Cobalt eluate because this stream is recycled in the
plant.
Furthermore, Cobalt eluate coming out during the 1st stage elution process
had Zinc in the range 0.2ppm-1.44ppm. At this stage, the ideal situation
was to have low concentration of Zinc in the Cobalt eluate because this
stream is recycled in the plant.
C. 2nd ELUTION USING 110 gpl H2SO4
0 2 4 6 8 10 12 140
0.2
0.4
0.6
0.8
1
1.2
1.4
0
50
100
150
200
250
3rd cycle Elution-2
Fe ppm Co ppm Cu ppm Zn ppm
TIME(MIN)
Fe ppmCo ppmCu ppmZn ppm
Figure 4.8 Zinc elution profile using 110 gpl H2SO4 at 5BV/hr. at ambient temperature
Figure 4.8 shows how the loaded Cu, Fe, Co, and Zn on resin were coming out.
The Zinc in the resultant solution;
WILLIAM C. MIINGA Page lxxi
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
The Zinc eluate coming out from the column had Copper, zinc and iron in
the range of 02ppm to 146ppm, 01ppm to 60ppm and <0.1ppm to 2ppm
respectively. The drop in the graphs shows the elution of these impurities
which were loaded on the resin. At this stage, the ideal situation was to elute
more Zinc in the zinc eluate because this stream is not recycled in the plant.
The Zinc eluate coming out from the column had cobalt in the range of
04ppm to 230ppm this is against 58ppm to 1.64 gpl in the cobalt elution.
This is a good recovery.
5.3.1. THIRD CYCLE SPLIT EFFICIENCY
1st ELUTION
Table 4.5 percentage split (3rd cycle) of Co, Cu, Zn and Fe in cobalt eluate using 5.6gpl H2SO4
Time(MIN)
Cumulative ,grams % in Co eluate
Co Cu Zn Fe Co Cu Zn Fe
10 0.16440.0008
00.0001
40.000010
093.3
3.9
2.3 5.3
20 0.25220.0015
00.0002
40.000020
093.8
6.3
1.7 7.8
30 0.30820.0020
00.0003
00.000030
093.4
7.8
2.0 9.2
40 0.34640.0023
00.0003
60.000040
093.8
8.5
2.2
10.3
50 0.36250.0025
00.0004
00.000050
094.0
8.9
2.5
11.3
60 0.36830.0027
00.0004
40.000060
094.1
9.6
2.8
13.3
2nd ELUTIONTable 4.6 percentage split (3rd cycle) of Co, Cu, Zn and Fe in zinc eluate using 110gpl H2SO4
Time(MIN)
Cumulative ,grams % in Zn eluate
Co Cu Zn Fe Co Cu Zn Fe
2 0.0060 0.0146 0.006000.0001
23.5
94.8
97.7
92.1
4 0.0118 0.0198 0.011300.0001
86.7
93.0
97.9
94.7
WILLIAM C. MIINGA Page lxxii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
6 0.0168 0.0222 0.014100.0002
46.2
91.7
98.3
92.2
8 0.0217 0.0237 0.015100.0003
06.6
92.2
98.0
90.8
10 0.0227 0.0249 0.015600.0003
56.2
91.5
97.8
89.7
12 0.02310.0255
00.01565
50.0003
96.0
91.1
97.5
88.7
For the Copper, Zinc, iron and Cobalt that was loaded on the resin, an average of 8
% Cu and 2% Zn, 93% Co and 8 % Fe went to the Cobalt eluate, which is suitable
for recycle back into the plant, and 91.5 % Cu, 97.6 % Zn, 6.5 % Co and 92.5% Fe
went to the Zinc eluate. Here the efficiency was also very good. Compared to the
other two cycles the third cycle’s split was very good. This was as a result of
changes made to optimize the cobalt eluate. The changes made were as follows;
Reducing the concentration of the 1st stage eluant from 9.4gpl to 5.6gpl H2SO4
Increasing the concentration of the 2nd stage eluant from 93.9gpl to 110gpl
H2SO4
WILLIAM C. MIINGA Page lxxiii
TM1(Solid/liquid separation)
Zn-SX plant
TM 2(Solid/liquid separation)
TM 3(Solid/liquid separation)
Cobalt recovery plant
O/F
U/FLarox (Gypsum)
Stripped liquor from Cu-SX plant
Feed (Tenke)
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
5.4. PROPOSED FLOWSHEET FOR Zn REMOVAL
TM= thickener number
O/F= thickener overflow
U/F= thickener underflow
TK= Tank
O/F
Zn≤ 10ppm
Resolution Stage
WILLIAM C. MIINGA Page lxxiv
Zn ≥100ppm
Zn ≤ 2ppm
Resolution Stage
Co eluate to TK10 clean up train
Zn eluate to Storage tank
Wash effluent to TK10clean up train
ISEP PLAN
Zn≤ 4ppm
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Figure 4.9: Proposed flow sheet for the removal of Zn from TM2 overflow
CHAPTER SIX
CONCLUSIONS AND RECOMMENDATION
WILLIAM C. MIINGA Page lxxv
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
6.1. CONCLUSIONS
From the investigation conducted through laboratory test works conclusively show
that;
The optimum Cobalt loading was achieved at pH=2.5 and flowrate
7.5BV/hr. for 1800 minutes.
The optimum cobalt elution was achieved with 5.6 gpl sulphuric acid. Of the
total cobalt that was loaded in the resins from the process solution, 93% Co
was split from zinc, copper and iron in cobalt eluate and of the zinc, copper
and iron that were in the resins an average of 8% Cu, 2.4% Zn and 8% Fe
went in Cobalt eluate. For The zinc impurities that were loaded in resins
from the process solution an average of 97.6% zinc was split from cobalt in
the Zinc eluate using 110g/l sulphuric acid.
Based on the results obtained the resin lewatit VP OC 1026 can be used to
remove zinc impurities from the cobalt streams of chambishi metals
purification circuit by ion exchange efficiently and
The current purification circuit flow sheet (figure 2.1) can be replaced by the
proposed purification circuit flow sheet (figure 4.9).
6.2. RECOMMENDATIONS
After looking at the split efficiency of elution for the ALL cycle process it is
recommended
That the procedure should be tried on a plant scale since this project was
based on the lab scale.
That acidic water be used during rinsing of the resins instead of tap water.
This is because the Resin lewatit VP OC 1026 resins are pH sensitivity. The
pH of rinse water should not exceed pH=4 because the resins becomes
unstable when pH=4 is exceeded.
WILLIAM C. MIINGA Page lxxvi
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
7. APPENDICES
Table 6.1 Loading profile results in the first stage
Temperature: AmbientFeed pH: 3.3Flowrate: 10BV/hr=20 ml/minResin volume: 120 ml
TIME (MIN)
Co gpl Cu ppm
Zn ppm Mn ppm
Mg gpl Fe ppm
0 8.579 381 3.57 471 1.919 2300 8.162 283 3.36 332 1.935 ˂0.1600 7.81 185 < 0.1 29 1.973 ˂1900 7.573 146 0.65
221.914 ˂1
1200 7.584 129 2.43 321 2.057 ˂11500 8.383 157 3.49 472 1.837 ˂11800 8.554 171 3.5 4
91.862 ˂1
Table 6.1.2 Cobalt elution results 1st stage
Flow rate: 5BV/hr= 10 ml/minResin volume: 120 ml
TIME(MIN)
Co gpl Cu gpl Zn ppm
Mnppm
Mg ppm e p
m10 1.50 2.131 146 247 50 1.1720 0.042 0.037 5 13 34 0.6130 0.019 0.012 2 3 23 0.640 0.007 0.005 ˂ 0.1 ˂ 0.1 20 0.5950 0.003 0.003 ˂ 0.1 ˂ 0.1 16 0.5360 0.002 0.002 ˂ 0. ˂
0.1 40.41
WILLIAM C. MIINGA Page lxxvii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
Table 6.1.3 Zinc elution profile results 1st stage
Flow rate: 5BV/hr. = 10 ml/minResin volume: 120 ml
TIME (MIN)
Co ppm
Cu ppm
Zn ppm
Fe ppm
Mn ppm
Mg ppm
2 60 9 40 171 16 424 33.5 9 22.8 150 16 306 7 8.5 5.6 114 3
08 4 8 2.4 85 1 810 3 7 1.1 83 1 812 2 6 0.8 0.5 1 8
Table 6.2.2 Cobalt elution results 2nd stage
Flow rate: 5BV/hr= 10 ml/minResin volume: 120 ml
TIME (MIN)
Co gpl
Cu ppm
Zn ppm
Mn ppm
Mg gpl Fe ppm
10 1.305 106 26 502 498 ˂0.120 0.599 28 24 60 172 ˂0.130 0.308 25 22 23 112 ˂0.140 0.145 23 20 10 115 ˂0.150 0.077 15 16 5 93 ˂0.160 0.056 10 9 3 88 ˂0.1
Table 6.2.3 Zinc elution profile results 2nd stage
Flow rate: 5BV/hr. = 10 ml/minResin volume: 120 ml
TIME (MIN)
Co gpl
Cu ppm
Zn ppm
Mn ppm
Mg gpl Fe ppm
2 70 13 12 7 40 35
WILLIAM C. MIINGA Page lxxviii
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
4 67 9 6 6 45 346 58 6 4.2 6 57 328 27 3 3.2 3 30 3010 12 1 1.88 1 18 ˂0.112 7 1 1.35 1 14 ˂0.1
Table 6.3 Loading profile results in the third stage
Temperature: AmbientFeed pH: 2.5Flow rate: 7.5BV/hr.=15 ml/minResin volume: 120 ml
TIME (MIN)
Co gpl
Cu ppm
Zn ppm
Mn ppm
Mg gpl
Fe ppm
0 8.563 381 3.57 471 1.919 2300 8.013 162 1.19 390 2.004 2600 8.202 164 0.85 393 2.044 1900 8.242 168 1.96 383 2.03 1
1200 8.378 172 2.81 372 1.981 11500 8.447 173 3.41 390 2.005 11800 8.588 182 3.48 377 2.007 1
Table 6.3.2 Cobalt elution profile results 3nd stage
Flow rate: 5BV/hr. = 10 ml/minResin volume: 120 ml
TIME(MIN)
Co gpl Cu ppm
Zn ppm
Mn ppm
Mg ppm
Fe ppm
10 1.644 8 1.44 12 53 < 0.120 0.878 7 0.98 11 50 < 0.130 0.56 5 0.6 10 47 < 0.140 0.382 3 0.55 3 27 < 0.150 0.161 2 0.47 2 15 < 0.160 0.058 2 0.4 1 10 < 0.1
Table 6.3.3 Zinc elution profile results 3nd stage
Flow rate: 5BV/hr. = 10 ml/minResin volume: 120 ml
WILLIAM C. MIINGA Page lxxix
Zinc Removal by ion exchange using lewatit vp oc 1026 Resin
TIME(MIN)
Co ppm
Cu ppm
Zn ppm
Mn ppm
Mg ppm
Fe ppm
2 238 146 60 338 993 1.174 228 52 53 97 541 0.616 209 24 28 46 327 0.68 49 15 10 25 247 0.59
10 10 12 5 20 120 0.5312 4 6 0.55 10 83 0.41
REFERENCES
Benefied, L. B. (1982). Chemistry for water and wastewater treatment.
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