School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING

Potokwe Tholego

Ramakoba Aubrey

Ranna W. Katlego

Othusitse Nhlanhla

Seporo Stephen

Shomana Thapelo

M3-Production of copper concentrate and 99.99% copper cathode from low-grade copper ore in Frank,

Northern Chile

Our mineral potential turns your world

4th May 2012

Introduction

Copper ore: 2.7 % (0.2 % chalcopyrite and 2.5 % Malachite/Azurite)

35 Mt reserve to be processed in 20 years, with annual production 1.75 million tonnes per annum.

To produce 99.9 % copper cathodes and 30 % copper concentrate

Introduction

Finance

Average Annual Profit:

US$ 180 million

Operating cost:

US$ 60 million per annum

Capital Cost:

US$ 325 million

NPV value US $848million

Production size: 39 900 tonnes cathodes and 10 000 tonnes concentrate per annum

The project is feasible and therefore recommended for a complete further review.

Overview of process

CRUSHER

SCREEN

HYDROCYCLONE

ROUGHER-SCAVENGER

Flotation reagents

Sulphide concentrate todewatering and drying

Tailings toleaching

MakeupSulphuricacid

AGITATION TANK

THICKENER

Tailings

Raffinate

SOLVENT EXTRACTION

ELECTROWINNINGCopper cathodes

FILTER

Water

CLEANERS

BALLMILL

TERTIARYCONE CRUSHER

PRIMARY CONECRUSHER

STOCKPILE

Enrichedelectrolyte

Depleted electrolyte

School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING

Crushing and GrindingThapelo Shomana

Size Reduction

Size Reduction

Why its important:

Make material easy to handle

Expose minerals for easily recovered

Increase homogenisation of ore

However too much liberation result in slimes which coat minerals and insufficient liberation lock minerals in rocks.

Crushing

Primary crushing gyratory crusher: 10 hours a day, 5 days in a week.

Leading to a crushing rate of 672 t/h.

Secondary and tertiary crushing cone crusher which will operate for 16 hours/day, 7 days, a week

Hence leading to a working rate of 300 t/h

Crushing

Gyratory Crusher

A gyratory crusher preferred over the jaw crusher

Main reason - more efficient as it crushes ore every time the mantle rotates hence why it is the most used in crushing hard mineral ores.

1219 x 2057 (size gape x mantle diameter),

Can operate up to 1330 t/h producing particles of about 120 mm.

Stockpile

A 2000 t stockpile on the surface

A conical stockpile used for its easiness in construction and

segregation minimised by multiple drawpoints on its bottom-tunnel reclaim system.

Tonnage (ton/m3 ) 33

Height (m) 10.15

Diameter (m) 27.12

Throat opening (mm) 360

Screening

 

Screen Area (m2)

Length (m)

Width (m) Depth of bed (cm)

Overflow (t/h)

Underflow (t/h)

Screen 1 3.125 2.5 1.5 7.8 250 50

Screen 2 3.125 2.5 1.5 7.8 200 50

Screen 3 (and 4)

6 3 2 2 46.65 100

Cone Crusher

Cone crushers are used in most plants for secondary and tertiary crushing.

They are the most efficient on the role

Specifications

Tertiary Cone Crusher:• Closed circuit, size 3050 mm• c.s.s. ≈ 11 mm

Secondary Cone Crusher:• Open circuit, size 3050 mm • c.s.s ≈ 25 mm

Cone size = Head Diameter, c.s.s. = closed side setting

Fine Ore Storage Bin

A 2000 t bin, mass flow system with a belt feeder

Lining: Bisalloy 360 Domite Ni Hard

Dimensions: Hopper angle, 20o; Height, 18.3

m; Opening diameter, 0.34 m; Shell diameter, 6.1 m

Grinding and classification

Ball Mill

Ball sizes, 14.96 cm Spout feeder preferred since its

suitable for hydroclone classifier Over-flow discharge mechanism will be

used 2 ball mills to operate:

Shell diameter, 4.45 m Inside diameter, 4.39 m Rubber lining, 0.18 thick with

waves Length 5.71 m 40 % by volume charge

Hydrocyclone

Due to inconsistent design data, a close example was used to estimate the shell diameter, Dc

The closest reference is the Africa u-ground concentrator with a product size of 100 µm.

The plant has 8 hydrocyclones with 0.25 m diameter, this is the size and the number of cyclones used in the project.

School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING

Froth Flotation

Aubrey Ramakoba

PROSS Flotation Flow sheet

CONDITIONING

Supplied by Denver Mineral Engineers Inc

• Xanthates• lime

Reagents

• 200 t/hr solids

• 600t t/hr water

Feed

8m

FLOTATION EQUIPMENT

MECHANICAL CELL

Drive mechanism

impeller

Cylindrical tank

PNEUMATIC MACHINE

FLOTATION CELLS

MECHANICAL MACHINESBetter suited for early stages

• Impellers makes it easy to float the valuable from the gangue

• Suitable where fines/slimes are present

PNEUMATIC MACHINESBest for cleaning stage;

• high recoveries and optimized grade

• One stage cleaning

• Cheap

• Easy to use

ROUGHER/ SCAVENGER CELLS

Distinctive features of Denver mechanical cell;

•Aeration can be easily controlled- supercharging can be employed for sluggish pulps

•No short circuiting

•No pumps needed to move pulp from one cell to another but uses gravity

•Selective flotation can be achieved as a result of the combination of machine features

ROUGHER/ SCAVENGER CELLS

Compared to the Denver cell;

• The Wemco cells lacks positive pull from the other cells to the impeller without a special pumping system.

• Pumps are needed to move the pulp from one cell to the other in the cells

CLEANER 2 EQUIPMENT

The main advantages of Metso columns are;

•Maximum particle-bubble contacts

•Effective reagent activation from the mechanical operation of the pump

•Wash water

•Increased carrying capacity

•Low operating cost

SUMMARY

Stage Equipment Supplier Size

Conditioning Conditioning tank Denver Minerals Engineers

22 m3

Roughers / Scavengers

Denver cells Denver Minerals Engineers

2.8- 36.1 m3

Cleaner 1 Denver cells Denver Minerals Engineers

2.8- 36.1 m3

Cleaner 2 Metso flotation column

Maelggwyn Mineral Services Limited

2.5 – 80 m3

School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING

Agitation Leaching

Wathuto Katlego Ranna

AGITATION LEACHING

WHAT IS IT?

Agitation leaching is a process where the ore is slurried with the extraction fluid for a period of time.

When equilibrium between the metal on the mineral surface and the metal contained by the solution is approached, the solubilisation of the metal in the solids is slowed, and the extraction is considered to be complete.

Comparison with other methods

•Agitation leaching provides a means for high recovery in short residence time.

•It is meant for ore that has high metal content

WHY AGITATION LEACHING

PROCESS DESIGN

Why Agitation•Needed to bring the lixiviant and ore into contact to recover the pregnant liquor.

•To maintain physical and chemical uniformity

•Finely ground ore solids are kept in suspension by use of agitators.

•Axial- flow impeller will be used, this design is said to be both energy efficient and mechanically sound for all agitation application.

•A more consistent mixture can be achieved by use of axial flow impellors

PROCESS DESIGN

Tank Sizing And Configuration•Leach tanks will be arranged such that the leach slurry flows by gravity from one tank to the next.

•Helps save on power that could be used to pump the slurry

•The operation is such that one tank is always free for maintenance and overflow emergencies

•Agitation tanks, agitator shafts and impellers will be constructed using mild steel as it is suitable for acidic conditions.

1/12 of the tank diameter

Case studies- A summary

The larger the surface area of exposed mineral, the higher the recovery

The following conclusions can be drawn from analysis of these case studies;

•Stirring speed and particle size are two of the most important factors in copper dissolution.

• Solubility of copper increases with decreasing particle size, and increasing stirring speed.

More important factors listed include reaction

temperature,

residence time and

a low solid-liquid ratio

KINETICS AND ADDITIVES

Sulphuric acid of pH 2

CuCO3Cu(OH)2 + 2H2SO4 2CuSO4 + 3H2O + CO2

Additive: Chloride

Chloride is an ideal surfactant for leaching: • It provides an ideal environment for the dissolution of

malachite.

• Enhances leaching as it facilitates electron transfer.

Oxide leaching is diffusion controlled

GANGUE AND ACID CONSUMPTION

Silicate gangue minerals are often present in oxide porphyry copper ores

CuSiO3.2H2O(s) + H2SO4 + 2H2O = CuSO4.5H2O(s) + SiO2(s)

Presence of Silicate minerals affects the amount of acid to be added for dissolution of copper.

This can be controlled by:

•Minimising residence time

•Operating at a temperature that is “just” ideal for dissolution of Copper

Presence of gangue such as silica and calcium can lead to problems such as gypsum precipitation in the copper recovery process.

Solution:

•Residence time = 5 hours

•Excess acid (dilute)

•25°C operating temperature

OPERATING CONDITIONS

Stirring speed – 480 rpm

particle size 0.1mm

temperature 25ºC

residence time 5 hours

solid-liquid ratio 30:70

Types of impellers: Axial Flow

CONCLUSION

•10% acid make up will be required

•Agitation is required to speed up the reaction kinetics

•Sulphuric acid will be used and mechanical agitation is the chosen method of keeping the solids in suspense.

•Mass transport is found to be high at low slurry densities (30:70)

To thickening and dewatering

School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING

Solvent Extraction

Tholego Potokwe

SOLVENT EXTRACTION

CHEMISTRY

Solvent extraction occurs in 2 stages

i) Extraction

2RH (org) + Cu2+ (aq) SO2-

4(aq) R2Cu (org) + 2H+(aq) + SO2-

4(aq)

ii) STRIPPING

R2Cu (org) + 2H+(aq) + SO2-

4(aq) 2RH(org) + Cu2+ (aq) + SO2-

4 (aq)

Where:

Cu2+(aq) - copper in the pregnant liquor,

2RH - the extractantR2Cu - copper extractant complex

2H+- acid in raffinate.

 

CHEMICAL SELECTION

EXTRACTANTS

Ketoximes Aldoximes

LIX 84-I (chosen)

LIX 622 LIX 984 M5640Operating conditions- 39% v/v required

-40ºC - pH 2

Advantages

-high chemical stability- Moderate strong extractant- work well in solutions with

High crud generation

PROCESS CHEMICAL SELECTION

Diluents

Reduce the viscosity of extractants

Shellsol 2046 (selected)

Low viscosity

Contains low aromatics

Has flash point

diluents

Shellsol 2325

-flash point 89ºC

-19% v/v aromatics

-viscosity 2.2

Shellsol 2046- 17% aromatics- Flash point 78ºC- viscosity 2.0

Orform

Flash point 77ºC

23% aromatics

PROCESS FLOW DIAGRAM

Merits

-Low capital cost

-Flexible operation

-High extraction efficiency

-Low solvent consumption

Circuit configuration

2E X 1S2E X 1EP X 2S

2E X 2S2E X 1EP X 2S

EQUIPMENT DESIGN AND SELECTION

Mixer settler designs

Four units designs: krebs, outokumpu vf, reverse flow and conventional mixer settler.Mixer

2 cylindrical mixing tanks per stage

Residence time : 3 minutes.

Tank volume = (solution flow rate x residence time)/effective volume

Tank volume: 6.62m3

Diameter=: 2.63m

EQUIPMENT DESIGN AND SELECTION

Curved bladed impeller

Fitted in the first mixer. Installed to generate the liquid liquid dispersion and to achieve the required head flow rate of the solution.

Advantages: low power consumption, low organic and air entrainment and high hydraulic efficiencies (35-45%).

A6000 HYDROFOIL IMPELLER

maintain the initial liquid-liquid dispersion generated by the curved bladed pumper.

Advantage: enhance high copper transfer at low power consumption.

Bladed cross section thickness and optimum twist and chamber has made it a better selection over other impellers.

EQUIPMENT DESIGN AND SELECTION

SETTLERS

Characteristics:

0.5m aqueous phase, 0.3 m organic layer, 1 m deep settler, residence time 5 minutes, settling area 3m3/hr m2.

Rectangular in shape.

Picket fences and chevrons for smooth flow.

Settling area =

Length=18m

Width 2.70

EQUIPMENT DESIGN AND SELECTION

Conventional Mixer settler

Meet the requirements of copper solvent extraction plant

Low power consumption and low organic air entrainments

Process optimisation and control are simple

Easy crud removal

SUMMARY

The whole plant will be 93% efficient

Electrolyte concentrated from 9.76g/l to 45g/l

LIX 84-I selected as the extractant

Conventional mixer-settler

School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING

Copper Electrowinning

Nhlanhla Othusitse

Electrowinning of aqueous electrolyte solution to produce 99.99% copper cathodes

What is electrowinning?

Solution discovery technique in which a metal is separated from solution by causing it

to deposit at the cathode when current is passed through the solution

Principle

H2OH+ + OH- 2H++ 2e-

E0=-1.23V

Cu2+(aq) + 2e- Cu(s)

E0=0.34V

Nernst Equation:It states that the standard electrode potential is the potential difference between energy states of products and reactants

Overall reaction

H2O+Cu2+ + SO2- 0.5O2 + Cu+2H++ SO2- Eo= -0.89V

PRROSS Copper EW

Electrowinningtankhouse

Electrode handling and cathode

stripping

Advanced electrolyte: 45g/L Cu & 170g/L H2SO4

1275m3/h

Spent electrolyte: 40g/L Cu & 190g/L H2SO4

510m3/h

765m3/h

456t of 99.99% harvested every 4days

Bleed electrolyte: 45g/L Cu & 170g/L H2SO4

Active storage tank 2900m3

Process conditions

Conditions

Acid mist management

balls and beads

mist suppression

foams

Good tank house

ventilation

Additives

Cobalt

Guar gum

balls and beads

Guar gum

Materials of construction

Equipment Chosen Other

Cell Polymer concrete lead, FRP and PP, HDPE plastics

Cathode 316L Stainless steel Copper starter sheet

Anode Pb-Sn-Ca Pb-Sb

Stripping Xstrata Robotic CSM ISA 2000 CSM, ISA Flexor stripper and roller stripper

Busbar Triangular Double contact

And ‘dogbone’ contact

Production

Number of cathodes

4250

Plating thickness, m

0.006

Mass of copper, kg/ cathode

107.28

Mass of copper harvested in 4 days, kg

455940

≈456t Cu

Plating rate, kg/h 1.12

The sizing of the EW plant by Farady’s law

Mass balance production known, so working out no. of cell = 4250

PRROSS EW tankhouse specifications

Production (tonnes. y-1) 39 900

Electrowinning cells

Length X width X depth (inside dimension of cell) m

5.5×1.1×1.2

Total number of cells 85

Anodes/cathodes per cell 51/50

Anode

material 98.5%Pb-1%Sn-0.5%Ca

Length X width X thickness /m

0.9 X 0.9 X 0.006

Cathodes

type ISA 316L Stainless Steel

Length X width X thickness /m

1 X 1 X 0.003

Electrolyte composition

Electrolyte feed

Cu/g.l-1 45

H2SO4/g.l-1 170

Spent electrolyte

Cu/g.l-1 40

H2SO4/g.l-1 190

Cell conditions

Cathode current efficiency/ %

90

Energy consumption/ kWh.kg-1Cu

1.87

Tankhouse representation

School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING

Tailings Management Facility

Stephen Seporo

LOCATION AND SITE CHARACTERISATION

Location: North Chile (Atacama desert)

Climate: Desert (precipitation less then 1mm per year).

Topography: Flat ground and sandy soils.

Hydrology: Very few surface and underground water resources

Geological hazards: High chances of earthquakes

INTRODUCTION TO TAILINGS STORAGE

TAILINGS STORAGE METHODS

SLURRY IMPOUNDMENT

-50% to 60% water

-Pumping possible

-Requires containment dam

PASTE

-35% to 40% water

-Pumping possible

-Do not segregate

DRY STACKING

-20% water

-Can not be pumped

-Dense and stable

WHY DRY STACKING…?

•Nature of the process

•Reduced water consumption

•Stable landform, reduced risk of impoundment failure

•Progressive rehabilitation of landform is possible

•Smaller footprint

THICKENING AND FILTRATION

Column thickener• 42.8 m diameter• Made of concrete

Horizontal belt filter• Filter leaf test for sizing

• Counter current washing

STACK DESIGN CONCEPT

•Transport and placement done using a conveyor and a radial stacker.

•Truncated square pyramid shape.

•Slope ratio 3H:1V and maximum height of 100m

•33 million tonnes of tailings produced over 20 years.

•Total footprint of 4800 hectares.

FOUNDATIONAND STABILITY

GEO-SYNTHETIC DRAIN: Allows seepage to drain from the stack

GEOSYNTHETIC CLAY LINER: Stops seepage from perforating into the ground

DRAINAGE BLANKET: Control subsurface water

REHABILITATION AND CLOSURE

Re-vegetation: Initial revegetation would involve seeding grass to help with stabilization and seeding of other native vegetation would follow thereafter.

Cover material: Required to resist runoff erosion, prevent dusting and create an appropriate growth media.