hit 200 e-waste document pdf-libre

FEASIBILITY STUDY FOR RECOVERING PRECIOUS METALS FROM E-WASTE.

GROUP MEMBERS ROPAFADZO JAMAKANGA H1210075N TINEVIMBO HOMERO H1210565J TAVONGA GUZURA H1210065D KUDAKWASHE KANENGONI H1210082C JONATHAN MADAMOMBE H1210164Y EFFORT B MUTAUTO H1210129P TINOTENDA KURWARA H1210065G

SUPERVISED BY

DR PHIRI MISS MALUNGA

THIS RESEARCH AND DEVELOPMENT WAS SUBMITTED TO HARARE INSTITUTE

OF TECHNOLOGY IN PARTIAL FULFILMENT OF THE BACHELOR OF

TECHNOLOGY (HONOURS) DEGREE IN CHEMICAL AND PROCESS SYSTEMS

ENGINEERING

2014

FEASIBILITY STUDY OF RECOVERING PRECIOUS METALS FROM E-WASTE 2014 ABSTRACT

Printed circuit boards (PCBs) from electronic gadgets at the end of their useful life period are

currently being dumped in landfills or incinerated, causing a serious environmental harm in the

form of toxic gases or leached hazardous compounds. PCBs contain high amounts of precious

metals; about 20 wt% copper, 0.04 wt% gold, 0.15 wt% silver, and 0.01 wt% palladium. The

extraction of these metals from PCBs is both profitable and environmentally worthwhile. Hence,

this study aims to design a commercial process to extract three of these metals, (copper, gold

and silver) from PCBs of computers and mobile phones. The proposed extraction process has

been divided into two stages: (1) physical separation, (2) metal recovery. Stage 1 involves size

reduction followed by the corona electrostatic separator and the hydro-cyclone which separates

metals from non-metals. Stage 2 separates individual target metals from each other by

hydrometallurgical processing. This stage involves leaching and precipitation of the metals into

their separate components. In a bid to develop an environmentally friendly technique for

recovery of precious metals from electronic scrap, a critical comparison of main leaching

methods is analyzed from both economic and environmental impact perspective. Experimental

results have shown that cyanide leaching is the best leaching method for this research’s target

precious metals from PCBs, on the basis of the economics, process applicability and

recyclability.

Keywords: Printed circuit boards (PCBs), recovery,

HIT 200 CPSE i

FEASIBILITY STUDY OF RECOVERING PRECIOUS METALS FROM E-WASTE 2014

DECLARATION

We, Effort B Mutauto, Tinotenda P Kurwara, Jonathan Madamombe, Tinevimbo H

Homero, Ropafadzo Jamakanga, Tavonga Guzura and Kudakwashe Kanengoni hereby do

declare that this work has not previously been accepted in substance for any degree and is

not being concurrently submitted in candidature for any degree.

Student Signature:

Effort B Mutauto ……………………………….

Tinotenda P kurwara …….…………………………. Jonathan Madamombe ………………………………….

Kudakwashe Kanengoni ………………………………… Tavonga Guzura …………………………………

Ropafadzo Jamakanga ………………………………… Tinevimbo H Homero ..………………………………..

Date / /

Supervisor‟s Signature: Dr Phiri ……………………………..

Miss Malunga …………………………….

Date / / HIT 200 CPSE ii


COPYRIGHT

All rights reserved. No part of this project may be reproduced, stored in any retrieval

system, or transmitted in any form or by any means, electronic, mechanical,

photocopying, recording or otherwise from scholarly purpose, without the prior written

permission of the authors and of Harare Institute of Technology on behalf of the authors. HIT 200 CPSE iii


DEDICATION

We dedicate this piece of work to our families, we appreciate their love, care, patience

and support.

HIT 200 CPSE iv


ACKNOWLEDGEMENTS

We would like to thank our supervisors Dr Phiri and Miss Malunga for their guidance through

which we managed to come up with this project. We would also like to thank Mr A Mukuya for

his encouragement, technical support and time sacrificed helping us. Our sincere gratitude goes

to all lecturers in the CPSE Department, Materials Department, CPSE laboratory staff,

families and friends for without them it would have been impossible for us to acquire the

knowledge and be able to undertake this project. Above all, we would like to thank the almighty

God for his tender mercy and for strengthening us in making this project a success.

HIT 200 CPSE v


ABBREVIATIONS

CPSE Chemical and processing systems engineering

EEE Electrical and Electronic Equipment

EMA Environmental Management Act

E-waste Electronic waste

HIT Harare Institute of Technology

ICTs Information Communication Technologies

PCBs Printed Circuit Boards

SMEs Small and Medium Enterprises

WEEE Waste Electrical and Electronic Equipment

ZIMSTAT Zimbabwe National Statistics Agency HIT 200 CPSE vi


TABLE OF CONTENTS

ABSTRACT ................................................................................................................................i

DECLARATION .......................................................................................................................ii

COPYRIGHT ........................................................................................................................... iii

DEDICATION ..........................................................................................................................iv

ACKNOWLEDGEMENTS ....................................................................................................... v

ABBREVIATIONS..................................................................................................................vi

LIST OF TABLES....................................................................................................................xi

LIST OF FIGURES.................................................................................................................xii

CHAPTER 1: INTRODUCTION ..............................................................................................1

1.1: Background ....................................................................................................................1

1.2: Problem statement ........................................................................................................... 2

1.3: Significance of the study ................................................................................................. 2

1.4: Justification......................................................................................................................3

1.5: Hypothesis of study.........................................................................................................3

1.6: Aim..................................................................................................................................3

1.7: Objectives........................................................................................................................3

CHAPTER 2: LITERATURE REVIEW....................................................................................4

2.1: Introduction.....................................................................................................................4

2.2: Health effects of electronic waste....................................................................................6

2.3: Current processes.............................................................................................................6

2.4: Separation of the individual valuable metals...................................................................8

2.5: Pyrometallurgical processes............................................................................................8

2.6: Bio leaching.....................................................................................................................9

2.7: Hydrometallurgical separation ......................................................................................10

2.8: Leaching agents ............................................................................................................. 11

2.8.1: Economics .............................................................................................................. 11

2.8.2: Process Applicability ..............................................................................................11

2.8.3: Toxicity...................................................................................................................11

2.9: Thermodynamic aspect of leaching .............................................................................. 11

2.10: Chemistry of cyanidation ............................................................................................13

2.11: Effect of cyanide concentration .................................................................................. 13

HIT 200 CPSE vii


2.12: Effect of hydrogen ion concentration .......................................................................... 14

2.13: Precipitation with zinc.................................................................................................14

2.14: Reaction chemistry ...................................................................................................... 14

2.15: Cyanide concentration ................................................................................................. 15

2.16: Zinc concentration ....................................................................................................... 15

2.17: Temperature ................................................................................................................15

2.18: Effect of pH .................................................................................................................15

2.19: Thiosulphate leaching ................................................................................................. 15

2.20: Effect of Na2S2O3 concentration .................................................................................16

2.21: Precipitation ................................................................................................................16

2.21.1: Sodium borohydride .............................................................................................16

2.21.2: Precipitation with sodium sulphide ...................................................................... 16

2.22: Leaching with HCL and HNO3 mixture (aqua regia) .................................................17

CHAPTER 3: RESEARCH METHODOLOGY......................................................................19

3.1: Interviews ......................................................................................................................19

3.2: Questionnaires ............................................................................................................... 19

3.3: Field work .....................................................................................................................20

3.3.1: E.M.A .....................................................................................................................20

3.3.2: Zimstat ....................................................................................................................20

3.3.3: Mbare magaba ........................................................................................................ 20

3.3.4: Research based on people’s activities to electronic gadgets domestic users: ...... 20

3.4: Results ...........................................................................................................................21

3.5: Materials and experimental procedure .......................................................................... 21

3.5.1: Dissolution of PCBs ...............................................................................................21

3.5.2: Recovery of metals by cyanide leaching and precipitation .................................... 22

3.5.3: Recovery of metals using aqua regia ...................................................................... 23

CHAPTER 4: RESULTS AND DISCUSSIONS .................................................................... 25

4.1: Survey results ................................................................................................................25

4.2: Dissolution 1 results ...................................................................................................... 26

4.3: Dissolution 2 results ...................................................................................................... 27

4.4: Calculations ...................................................................................................................28

4.5: Cyanide leaching ...........................................................................................................30

HIT 200 CPSE viii


4.6: Precipitation ..................................................................................................................31

4.7: Aqua regia leaching and precipitation........................................................................... 31

4.8: Analysis of results ......................................................................................................... 32

CHAPTER 5 PROCESS DESIGN ..........................................................................................36

5.0: Introduction ...................................................................................................................36

5.1: Block flow diagram ....................................................................................................... 36

5.2: Mass balance .................................................................................................................37

5.3: General mass balance equation .....................................................................................37

5.4: Overall mass balance..................................................................................................... 38

5.5: Energy Balance ............................................................................................................. 39

5.5.1: Overall balance for process ........................................................................................40

5.6.: Process flow diagram ................................................................................................... 41

5.7: Process description ........................................................................................................ 42

5.7.1: PCB sampling and dismantling ..................................................................................42

5.7.2: Separation techniques................................................................................................. 42

5.7.2.1: Electrostatic separator .........................................................................................42

5.7.2.2: Eddy current separator .........................................................................................43

5.7.2.3: Magnetic separator ..............................................................................................44

5.7.3: Cyanide absorption chamber ......................................................................................44

5.7.4: Cyanide Treatment: ozone oxidation ......................................................................... 45

5.7.4.1: Advantages of Ozone Oxidation on cyanide treating ............................................. 46

5.8: Process innovation ........................................................................................................ 46

5.9: Process control .............................................................................................................. 46

5.9.1: Process instrumentation and control .......................................................................... 46

5.9.2: Control system characteristics ...................................................................................46

5.9.2.1: Mode of control algorithm...................................................................................47

5.9.3: Alarms, safety trips and interlocks ............................................................................. 47

5.9.4: Process control of the leach reactor ........................................................................... 47

5.9.4.1: Temperature control system ................................................................................48

5.9.4.2: PH control systems ..............................................................................................48

CHAPTER 6: ECONOMIC ANALYSIS ................................................................................50

HIT 200 CPSE ix


6.1 Introduction ....................................................................................................................50

6.2: Sales calculations .......................................................................................................... 52

6.3: Total cost ....................................................................................................................... 52

6.4: Profitability evaluation .................................................................................................. 54

6.5: Break even analysis ....................................................................................................... 54

CHAPTER 7: CONCLUSION AND RECOMMENDATIONS .............................................56

7.1: Conclusion.....................................................................................................................56

7.2: Recommendations ......................................................................................................... 56

7.3: References .....................................................................................................................57

HIT 200 CPSE x


LIST OF TABLES Table 1 : List of substances contained in electronic waste ......................................................11

Table 2: Methods of metal reclamation, hazards, energy, and environment impact ............... 14

Table 3: Leaching agents used in processing ........................................................................... 19

Table 4: Dissolution 1 results .................................................................................................. 33

Table 5: Dissolution 2 results .................................................................................................. 34

Table 6: Calculations of power consumption in experiment 2 ................................................36

Table 7: Leaching solution preparation and reagents consumption ......................................... 37

Table 8: Amount of gold recovered from precipitation at pH 11.8 ......................................... 38

Table 9: Amount of gold after precipitation at pH 12.4 ..........................................................38

Table 10: Amount of gold recovered by precipitation .............................................................38

Table 11: Amount of gold left in solution after precipitation ..................................................39

Table 12: Gold precipitated recovered by smelting using borax flux ...................................... 39

Table 13: Comparison of different lixiviants ........................................................................... 40

Table 14: Scaling up of mass balance ......................................................................................46

Table 15: Power consumption ................................................................................................. 47

Table 16: Direct costs for the recycling process ...................................................................... 57

Table 17: Indirect costs ............................................................................................................ 58

Table 18: Summary of equipment costs...................................................................................58

Table 19: Metal prices .............................................................................................................59

Table 20: Direct manufacturing costs ......................................................................................59

Table 21: Fixed manufacturing costs .......................................................................................60

Table 22: Total Manufacturing costs .......................................................................................60

HIT 200 CPSE xi


LIST OF FIGURES Figure 1: Potential /pH for gold- water system ........................................................................ 19

Figure 2: Effect of KCN concentration on rate of dissolution .................................................20

Figure 3: Effects of sodium thiosulphate concentration on extraction of gold ........................23

Figure 4: Percentage leached by an agent at different temperatures ....................................... 24

Figure 5. Percentage leaching yield using HNO3 ..................................................................................................... 25

Figure 6: Percentage Leached using H2SO4 ................................................................................................................. 25

Figure 7: Old computers at HIT ...............................................................................................26

Figure 8: Dysfunctional phones ...............................................................................................26

Figure 9: Mass of NaCN consumed with time......................................................................... 37

Figure 10: Amount of gold leached by different leaching agents ............................................ 41

Figure 11: Amount of gold precipitated with different precipitating agents ...........................42

Figure 12: Block flow diagram ................................................................................................43

Figure 13: Mass balance chart ................................................................................................. 44

Figure 14: Process flow chart of the whole process ................................................................48

Figure 15: Electrostatic separator ............................................................................................50

Figure 16:Eddy current separator.............................................................................................50

Figure 17: Magnetic separator .................................................................................................51

Figure 18: Break even chart ..................................................................................................... 62 HIT 200 CPSE xii


CHAPTER 1: INTRODUCTION

In recent years, a dramatic increase in the production and consumption of electrical and

electronic equipment (EEEs) with a sharp decrease in their lifespan has led to the generation

of large quantities of waste. E-waste as this waste is popularly known, is the waste near or at

the end of their useful life period and are of no further use. These include computers, cell

phones, TVs, radios, printers and calculators. WEEE is the fastest growing waste stream in the

world with a 3-5% increasing rate per year than generation of municipal wastes. E-waste

contains several different substances and chemicals, many of which are toxic and are not

biodegradable and are likely to create adverse impact on environment and health, if not handled

properly. The random disposal and improper dismantling practices produce various toxic and

carcinogenic substances which are harmful to the environment and human health. Heart

failures, cancer, inflammation and oxidative stress and kidney failures are diseases caused by

randomly disposing e-waste. Due to organic and inorganic hazardous materials present in e-

waste, a proper management method is required. Since e-waste contains appreciable amounts

of precious (Au, Ag, Pd etc.) and base (Cu, Pb, etc.) metals, it is potentially an important

secondary sources of these metals (Hagelüken, 2006; Yazici et al., 2011). 1.1: Background

The growing quantity of e-waste from electronic industry is beginning to reach disastrous

proportions. It is estimated that the world generates 20-50 million tonnes annually (Herat

2013). The United States of America is the largest producer of e-waste producing three million

tonnes annually. In South Africa and China for example, it is predicted that by 2020 e-waste

from old computers will have jumped by 200 to 400 percent from 2007 levels, and by 500% in

India(Science News 2010). Internationally, various legal frameworks have been enacted and

enforced to regulate E-waste.

Zimbabwe is also not exempted from the problem of e-waste as it is also facing a rising tide of

e-waste generated by domestic consumption of new and used electrical and electronic

equipment (Newsday 20-08-12). The rate at which cheap electronic gadgets for retail are

flooding the local market could be viewed by some as development but it is also contributing

to the increase of e-waste as these gadgets have a short life span. However, there is no

environmentally friendly method to dispose e-waste and the government has been urging HIT 200 CPSE Page 1


institutions and industries not to dispose of dysfunctional electronic gadgets. This means

sources of raw materials are attainable and readily available. Local electricians can also be a

good source of the raw materials. Zimbabwean laws to consider for legal operation of this project:

Waste Management Enterprises (section 14 to 21-regulations) which require all persons

operating waste collection enterprises or waste management to be licensed,

Rural and urban councils act

Mines and minerals act

Need to comply with rules and regulations of EMA.

1.2: Problem statement

Electronic waste deposition and incineration, without recycling the non-renewable resources

present in it, is an energy inefficient and environmentally unfriendly process of e-waste

disposal. There is therefore need for a recycling (metal recovery) process that is both

economically active and environmentally friendly. The feasibility study for such a process is

to be carried out. 1.3: Significance of the study E-waste is extremely important in diverting solid waste and supporting zero landfill initiatives.

It helps prevent and eliminate toxic scrap. The environmental impact of metal production is

quite significant especially for precious and special metals. To produce one ton of gold, 10000

tons of carbon dioxide is generated. If recycling processes are used to recover metals from e-

waste, only a fraction of carbon dioxide emissions will occur apart from other benefits already

previously stated. Processing of e-waste is most justified not only because of the impact they

can have on environment in case of un-controlled handling, but is also connected with profits

resulting from the possibility of recovery of valuable components. Undoubtedly, the

quantitative composition of electronic waste equipment makes this type of waste material

attractive in terms of possibility of metal recovery. Particularly rich in these ingredients are

printed circuit boards (PCBs), which are part of electronic devices, among which copper is the

dominant component.

HIT 200 CPSE Page 2


Currently in Zimbabwe end of life electronic products are discarded in landfills, burnt in open

air or collected by electronic repairers. By implementing the ‘3 Rs’ Reduce, Recycle, Reuse

and the green technology, the problem of e-waste can be reduced, thus e-waste can be utilised

as raw materials for secondary source of precious and base metals. 1.4: Justification

Economic - e-waste recycling enables recovering of renewable resources which serve

as a secondary source of metals.

Socio-economic - recycling of e-waste is a social benefit as it creates employment for

the recycling industry.

Environmental - This project recovers metals in an environmental friendly way and

also reduces the land degradation as compared to the present practice. 1.5: Hypothesis of study

Ho: If a cost-effective, high efficient, safe and eco-friendly recycling process is attained, the

process is feasible.

H1: If a low-effective, less efficient and high hazardous process is attained, the process is a

total failure. 1.6: Aim

To determine the economic and environmental feasibility of recovering metals from e-waste. 1.7: Objectives

To recover metals through a profitable and highly efficient process

To conserve the limited non-renewable resources through recycling and reducing

overall land digging as the only source to get the metals.

To reduce burning of e-waste in open environment or uncontrolled burning

HIT 200 CPSE Page 3


CHAPTER 2: LITERATURE REVIEW

2.1: Introduction E-waste statistics

Compared to the other components which make up electrical gadgets, printed circuit popularly

known as PCBs contain relatively high amounts of precious metals. Youssef (2012) projects

that PCBs of computers and mobile phones are rich in precious metal content and are the most

abundant since they are the backbone of most electronics. The values of metal compositions of

PCBs from different sources like televisions, personal computers, DVD players, calculators

and others were obtained and analyzed to conclude that PCBs from personal computers and

mobile phones contain the highest amounts of valuable metals (Youssef 2012). Table 1 below

shows substances contained in various components of electronic waste. Table 1: List of substances contained in electronic waste

Metal

by %

Key

Boards

Personal

computers

Printed circuit

board

Car

electronics

Typical

copper

ore

Recycling

efficient

%

Ag 0.05 0,009 0,3 0,12 0,00034 80

Au 0.005 0.001 0.008 0.007 0,00001 99

Cu 13 7 25 20 0,8 90

Zn 3 1.2 1.5 1 0.12 60

Pd O,0002 0.0004 - - 0,04 60

Al 18 11 3 - - 80

Ni 0,16 0.2 0.5 0.3 - 0

Pb 0.3 1.5 - 1 - 5

Bi <0,000

3

<0.0004 0.17 0.01 - 6

Fe 3 <0.1 5 5 - 80

Sb 0.3 0.5 0.06 0.08 - 70

(Proceedings of the International Conference on Sustainable Solid Waste Management, 5 - 7

September 2007, Chennai, India. pp.155-162)

Currently, half million tonnes of e-waste is discarded each year in India.

HIT 200 CPSE Page 4


Recognizing the opportunity to turn an environmental disaster into a business plan in 2007,

Gupta and his brother launched Attero (a Latin name for waste). Today, Attero is the

leading e-waste recycler in India, according to Gupta, handling almost 500 tons of e-waste

every month. The company's success is based on its widespread collection system, now

operating in 22 states across the country, and its innovative, four-stage recycling technology,

which recovers valuable metals - rare earths, precious metals and base metals-without fouling

the local environment. Its process is also cheaper than existing methods, says Gupta, so it can

operate profitably in areas with limited amounts of recyclable material to feed the process.

Tanzania has no specific policy on e-waste management but a number of policies which aim at

protecting the environment and human health are in place. Among the existing policies relevant

to e-waste management are the National Environment Policy (1997); Sustainable Industrial

Development Policy (SIDP) 1996 - 2020; National Water Policy (2002); National Energy

Policy (2003); National Trade Policy (2003); Small and Medium Enterprises (SMEs)

Development Policy (2003); the National Health Policy (2003); Science and Technology

Policy (1996); and the National Information and Communications Technologies (ICT) Policy

2003.

Hischier et al (2011 ), in their publication entitled “Does WEEE recycling make sense from an

environmental perspective?” established that throughout the complete recycling chain the

sorting and dismantling activities of companies are of minor interest; instead the main impact

occurs during the treatment applied further downstream to turn the waste into secondary raw

materials. The conclusion was reached by examining two Swiss take-back and recycling

systems of SWICO (for computers, consumer electronics and telecommunication equipment)

and S.EN.S (household appliances). The two systems, which are based on an advanced

recycling fee, are well established within Switzerland. With a combined approach of material

flow analysis and life cycle assessment, the environmental impacts of these two systems have

been estimated, including all further treatment steps, which transform the fractions either into

secondary materials or into waste for final disposal. As a baseline, they used a scenario

assuming that no e-waste is recycled and hence only primary production for the similar amount

of raw materials. When comparing the environmental impact of e-waste recycling with that

HIT 200 CPSE Page 5


derived from the baseline scenario (incineration of all e-waste and primary production of the

raw materials), recycling proves to be clearly advantageous from an environmental perspective. 2.2: Health effects of electronic waste

Arsenic may disrupt cell communication and interfere with the triggers that cause cells to grow,

possibly contributing to cardiovascular disease, cancer and diabetes if someone is exposed in

chronic, low doses. Cadmium affects your body's ability to metabolize calcium, leading to bone

pain and severely weakened, fragile bones. Chromium can cause skin irritation and rashes. It

is also potentially carcinogenic. Copper can irritate the throat and lungs and affect the liver,

kidneys and other body systems. Lead poisoning can cause a whole slew of health problems

including the impairment of cognitive and verbal activity. Eventually, lead exposure can cause

paralysis, coma and death. Nickel is carcinogenic in large doses. Silver probably won't hurt

you, but handle it too frequently and you might come down with a case of argyria -- a condition

that permanently stains your skin a blue-grey shade. (UNEP, Recycling- From E-Waste to

Resource accessed at www.unep.org, on 24 Jan 2014). 2.3: Current processes It is mainly the developed countries and a few other developing countries like South Africa and

Tanzania which are recovering metals from PCBs. The processes in Table 2 below are the ones

which are currently being used. HIT 200 CPSE Page 6

http://www.unep.org/


Table 2: Methods of metal reclamation, hazards, energy, and environment impact Process Energy reuse Metal reclamation Environmental impact

Shredding Low; non-metals are

landfilled

High; metals sent to

smelter High

Municipal

incineration

High, as this process

aims to maximize this None, unaddressed

All toxins either released

through smoke or slag

Pyro metallurgical

recovery

Low, non-metals not

included in scope High

Large energy

Requirements

Thermal

depolymerisation

High, waste

transformed into

useable materials

None, unaddressed Low, efficient process,

organic toxins

decomposed

Plasma arc

gasification

High, waste

transformed into

useable materials and

power

None, unaddressed

Low, efficient process,

toxins decomposed

Bioleaching

Low, non-metals are

landfilled

High, many metals

have 90% recovery

rates

Very low energy process

The separation of metals from non-metals provide the appropriate further conditions for further

processing which involve the use of chemical reagents and solvents. There are different

possible approaches to separate metals from non-metals in PCBs which mainly involve

incineration, acid washing or physical separation. In order to recover valuable materials and to

minimize the adverse effects of hazardous materials contained in PCB, technologies such as

copper-smelting method (Andrea et al 2012). HIT 200 CPSE Page 7


Incineration- is a treatment process that involves the combustion of organic substances

contained in waste materials. It can be used to burn off the non-metallic parts of PCB and retain

the metals from the ashes. However, waste incineration causes release of hazardous gases such

as dioxins and furans which can cause severe harm to the environment.

Acid washing/bathing- can be also used to react with the non-metallic parts of PCB and recover

the metals either from the rich solvent or as precipitates. However, the process of acid washing

is very difficult to control especially when including the non-metallic parts of PCBs as it causes

release of hazardous vapors and fumes.

Physical separation techniques- can also be used to separate the metals and non-metals from

PCBs. Such techniques are known to have safe and eco-friendly operation. Although they are

energy intensive, physical separation technologies are able to produce separate streams of

metals and non-metals. Such separation paves the way either for more profit from sales of waste

plastics and ceramic, or for more future development in the area of recycling of plastics. 2.4: Separation of the individual valuable metals

This is the stage where all the metals of interest are separated from the mixture and extracted

as pure metals which can be sold.

The metals selected for recovery in this study are gold, silver and copper. Therefore, a process

is needed which can selectively and quantitatively separate each of these metals from the

mixture, taking into consideration all other possibly present metal. 2.5: Pyrometallurgical processes

Pyrometallurgical processes include incineration, smelting in a plasma arc furnace or blast

furnace, drossing, sintering, melting and reactions in a gas phase at high temperatures.

Incineration is a common way of getting rid of plastic material and other organics to

further concentrate the metals . The crushed scrap can be burned in a furnace or in a molten

bath to remove plastics, leaving a molten metallic residue. The plastic burns and the refractory

oxides form a slag phase. In smelting reactions a collector metal such as copper or lead can be

used. But also impure alloys can be made by smelting the crude metal concentrates. Silver and

gold containing scrap materials can be treated in a copper smelter, but silver as well as other

noble metals are tied up in a process for a long period. The majority of secondary

HIT 200 CPSE Page 8


copper and a main part of the electronic scrap is processed pyrometallurgically in a

copper smelter, which include steps as reduction and smelting of the material, blister or

raw copper production in the converter, fire fining, electrolytic refining and processing of

the anode mud. In a modern secondary copper smelter, many different kinds of copper

containing materials are recycled. The materials(e.g. electronic scrap) are fed into the

process in different steps depending on their purity and physical state. The anode

composition and the quality of the dust and slag fluctuate significantly due to the

heterogeneity of the input materials. Advantages

Proven technology

Disadvantages

It is capital and high energy intensive

It produces toxins

Requires high values of residual metals

Complex

It needs special materials to handle highly corrosive agents such as aqua regia. 2.6: Bio leaching (use of bacteria and fungi to extract metals from e-waste)

Microbiological processes can be applied to mobilize metals from electronic waste materials.

Bacteria (Thiobacillus thiooxidans, T ferrooxidans) and fungi (Aspergillus niger, Penicillium

simplicissimum) can be grown in the presence of electronic scrap. The formation of inorganic

and organic acids caused the mobilization of metals. Initial experiments showed that microbial

growth was inhibited when the concentration of scrap in the medium exceeded 10 g per L

.However, after a prolonged adaptation time, fungi as well as bacteria grew also at

concentrations of 100 g per L . Both fungal strains can mobilize Cu and Sn by 65%, and Al,

Ni, Pb, and Zn by more than 95%. At scrap concentrations of 5-10 g per L Thiobacilli is able

to leach more than 90% of the available Cu, Zn, Ni, and Al. Pb precipitated as PbSO4 while

Sn4 precipitated probably as SnO. For a more efficient metal mobilization, a two-step leaching

process is proposed where biomass growth is separated from metal leaching. Microbiological

leaching uses a natural ability of microorganisms to transform metals present in the waste in a

solid form (in the solid matrix) to a dissolved form. Apart from the possibility of bioleaching

HIT 200 CPSE Page 9


of metals in alkaline environment (involving cyanegenic bacteria), acidophilus microorganisms

and conducting biological process of leaching in an acidic environment play a crucial role in

the bio-metallurgical techniques. Bio-metallurgical processing of solid waste is similar to

natural biogeo-chemical metal cycles and reduces the demand of resources, such as ores,

energy and landfill space. Advantages

is cheaper and easier to conduct in comparison to conventional techniques

is flexible - microorganisms easily adapt to changing and extreme living conditions is

environmentally friendly

It is considered a green technology (generates less amount of waste)

This is why more and more scientists become interested in bio metallurgy, technology which

can provide an attractive alternative to currently used physical and chemical methods to recover

valuable metals from waste. Disadvantages

The speed at which the bacteria can dissolve metal is a significantly slow process

It requires the material being leached to be extremely small i.e. <0,5mm 2.7: Hydrometallurgical separation

In hydrometallurgical treatment the main steps are acid or caustic leaching of solid material.

This process normally requires a small grain size to increase the metal yield. From the solutions

the metals of interest are then isolated and concentrated via processes as solvent extraction,

precipitation, cementation, ion exchange, filtration and distillation. Leaching solvents are

mainly H2SO4 and H2O2, HNO3, NaOH, HCl etc. Hydrometallurgical processes provide high

selectivity, high purity output, controlled environment, and good recovery. Hydrometallurgical

approaches depend on selective and non-selective dissolution to achieve a complete

solubilisation of all the contained metallic fractions within e-scrape waste. Advantages

Potential low energy input

Simple proven technology

HIT 200 CPSE Page 10


Provides high selectivity,

High purity output,

Controlled environment, and good recovery

Disadvantages

Non selective - low value metals such as iron are dissolved

Problems recovering the valuable metals from dissolved iron

Highly corrosive solutions

High use of water and/or chemicals with downstream treatment considerations 2.8: Leaching agents

The choice of leaching agents depends on:

2.8.1: Economics

Capital investment

Extraction economics

Availability

Cost considering detoxify/recycling 2.8.2: Process applicability

Limitations (e.g. ore type, selectivity, control, separation)

Recyclability

Detoxificability

Large scale applications (proven technology)

2.8.3: Toxicity

Emissions

Handling

Environmental toxicity 2.9: Thermodynamic aspect of leaching Copper, Gold and silver are very noble and the potentials are Au + 3e- = Au3+ ; Cu + 2e = Cu 2+ and Ag + e- = Ag+. The equilibrium of gold is more positive even than that of oxygen

reduction reaction as shown in Fig.1. Thus it can be seen that gold is highly stable in aqueous

solution and indicates that it cannot dissolve in non-complexing solutions in the presence of



oxygen. Also silver and copper are highly non-reactive with air. This is indeed the case in

practice, the metals being unaffected by weak acids and the other metals above hydrogen in the

series being easily leached (potassium, zinc calcium).

This suggests that the leaching of the metals may prove difficult difficult as we go down the

reactive series. However, the presence of complexing agents can considerably modify

potential/pH diagrams for metal-water systems due to the formation of highly stable metal

complex ions. Table 3 shows possible leaching agents for the processing and the active

substrates.

Figure 1: Potential /pH for gold- water system

Table 3: Leaching agents used in processing Metal Leaching Agent

Base Metals Nitric Acid

Gold and Silver Cyanide or Thiosulphate

Copper Sulphuric Acid or Aqua Regia

Palladium Hydrochloric and Sodium Chlorate


Rat

e


2.10: Chemistry of cyanidation

It is one of the earliest devised leaching processes in which oxygen participates via the

atmosphere involves the dissolution of alkaline cyanide solutions, the overall reaction of which

may be represented as: 4Au + 8CN- + O2 + 2H2O 4Au (CN)-2 + 4OH-

2 CuSO4 + 4 NaCN → 2 CuCN + (CN)2 + 2 Na2SO4

2Ag + 4CN- +O2 + H2O = 2Ag(CN)2- + 2OH- +H2O

A high pH (usually 10.5-11 range) is necessary to ensure that most of the cyanide is in the ionic

form. A high pH is also necessary for safety and economic reasons as HCN is a volatile and

poisonous gas. 2.11: Effect of cyanide concentration The rate of dissolution increases linearly with increasing cyanide concentration until a

maximum is reached, beyond which a further increase in cyanide does not increase the amount

of metal dissolved, but on contrary has a slight retarding effect as shown in Fig 2 below. 0 0.2 0.4 0.6 0.8 1

KCN Concentration

Figure 2: Effect of KCN concentration on rate of dissolution



The decrease in the rate at high cyanide concentration is due to the increase in pH of the

solution. Cyanide ion undergoes hydrolysis according to the reaction: CN- + H2O HCN + OH-

This reaction is undesirable since there is production of HCN fumes which are toxic. 2.12: Effect of hydrogen ion concentration

It is essential that cyanide solution is kept alkaline during leaching of gold because of the

following reasons: Prevent hydrolysis of CN- ion. CN- + H2O HCN + OH-

Prevent cyanide decomposition by atmospheric CO2.

CN- + H2CO3 HCN + HCO-3

Dissolution of base metals such as copper, zinc and nickel is substantially reduced and

resulting in cleaner effluents than those generally produced in acid leach systems. 2.13: Precipitation with zinc

Gold is precipitated out of the pregnant solution by means of zinc powder. The precipitate is

then filtered out of the solution, and the filtrate (which looks like grey mud at that point) is then

smelted with fluxes to recover the gold bullion. 2.14: Reaction chemistry

The anodic oxidation of zinc in aqueous solution is given by: Zn2+ + 2e Zn

In cyanide solution zinc forms a stable cyanide complex: Zn2+ + 4CN- Zn(CN)42-

Combining these equations gives: Zn(CN)42- + 2e- Zn + 4 CN-

2 Au(CN)2- + Zn 2 Au + Zn(CN)42-



2.15: Cyanide concentration The rate of precipitation is independent of cyanide concentration above the critical minimum

value. However, the dissolution rate of zinc increases with increase in cyanide concentration

and hence it is undesirable to increase cyanide concentration significantly above the minimum

required for precipitation. 2.16: Zinc concentration

The dissolution rate of zinc decreases with increasing Zn ion concentration. High zinc

concentration can result in formation of insoluble zinc hydroxide which can passivate the zinc

surface and severely reduce precipitation rate. 2.17: Temperature

Elevated temperatures increase the rate of zinc dissolution and hydrogen evolution, with an

associated decrease in precipitation efficiency. Under these circumstances, the addition of Pb

(II) may reduce Zinc consumption and improve precipitation efficiency. 2.18: Effect of pH

The pH of the pregnant solution also influences the redox potential, which shifts in the negative

direction with increasing alkalinity. The cementation process improves when there is an

increase in pH to a value between 11.5 and 11.9. Precipitation is severely retarded below pH

8, and the, the precipitation rate has been found to drop sharply at pH values above 12 due to

excessive hydrogen evolution. Consequently industrial systems usually operate within the

range applied for cyanide leaching i.e. pH 10.5-11.5 (or approximately 0.10-0.20g/l Ca(OH)2). 2.19: Thiosulphate leaching The leaching with thiosulphate is considered as a promising alternative to cyanide leaching.

Thiosulphate based on other experimental results is the only process which can be used directly

to leach gold from certain gold containing sulphide ores without a pretreatment step such as

roasting, high pressure oxidation or bacteria l leaching and also without the consumption of

large amounts high cost or toxic leaching agents. The gold in leach solution can be cemented

with zinc dust, sodium borohydride or with sodium sulphide. HIT 200 CPSE Page 15

% E

xtra

cted


2.20: Effect of Na2S2O3 concentration The effect of thiosulphate concentration on gold extraction is shown in fig 3 below. It can be

seen that the gold extraction generally increased with the increase in thiosulphate concentration

up to 1.0M, and then the extraction decreased with further increase in thiosulphate

concentration. The extent of gold extracted has shown a minimum roughly at 0.6 Na2S2O3. 100

80

60

40

20 0

-0.4 0.1 0.6 1.1 1.6

Concentration (M)

Figure 3: Effects of sodium thiosulphate concentration on extraction of gold 2.21: Precipitation 2.21.1: Sodium borohydride Gold can be precipitated by reduction onto Zn, Al or Fe powder with sodium borohydride. BO33- + 7H2O + 7e = BH4 + 10OH-

Au(S2O3)23- + e = Au + 2S2O32

2.21.2: Precipitation with sodium sulphide

Generally, a large excess of metal powder is required to provide sufficient surface area to

reduce gold in a reasonable time. Unfortunately, copper also co-precipitates from solution and

must be recycled to leach - except when copper powder is used. Interestingly, fundamental

electrochemical studies report that Au (I) thiosulphate cannot be readily reduced to metallic

gold in the potential region where copper dissolve. However, the presence of both copper and HIT 200 CPSE Page 16


silver in solution enhances gold deposition at a low over potential (i.e. gold deposits readily on

silver). 2.22: Leaching with HCL and HNO3 mixture (aqua regia)

Mixing 1 volume of concentrated nitric acid with 4 volumes of concentrated hydrochloric acid

makes aqua regia. No heat is evolved when mixing but the aqua regia at once starts to emit

chlorine gas, which evolves slowly for several days. A closed aqua-regia vessel can develop

enough chlorine pressure to burst. So the bottle needs to be stored in the open or in a fume

hood. The effect of temperature on the leaching agent is shown in fig 4, Fig 5 and Fig 6 Aqua regia attacks the metal with formation of [AuCl4] - complex ion. Au + 6HNO3 Au3+ + 3NO3- + 3H2O + 3NO2+ 4Cl- (from conc HCl) [AuCl4]-

Gold is first oxidized by nitric acid to Au3+, which is then removed by complexing with the

chloride ions.

45

40

35

30

25 25°C

20 95 °C

15

10

5

0 H2SO4 1M HCL 2M HNO3 2M

Figure 4: Percentage leached by an agent at different temperatures HIT 200 CPSE Page 17

FEASIBILITY STUDY OF RECOVERING PRECIOUS METALS FROM E-WASTE 2014 120 100 80 60

25°C

90°C

40 20

0

Cu Fe Ni Zn Pb Al Ag Sn

Figure 5. Percentage leaching yield using HNO3

70

60

50

40 30 20 10 0

Cu Fe Ni

Zn Sn Pb

25°C

90°C

Al Ag

Figure 6: Percentage Leached using H2SO4



CHAPTER 3: RESEARCH METHODOLOGY

3.1: Interviews

Interviews were conducted. Areas where interviews were conducted include the HIT Electronic

Engineering department, Environment Management Agency, Zimstat offices and people

(domestic users) around Zimbabwe in relation to the research team residence 3.2: Questionnaires

These were issued out to the offices and department of the school. HIT ICTS department

managed to help with the figures of electronic gadgets which are no longer in use, from some

of their storerooms to be 793+. Figure 7 shows the state of the HIT ICTS department and Figure

8 show dysfunctional phones. Other departments could not manage to give the values since it

is confidential information and required many offices to get it.

Figure 7: Old computers at HIT

Figure 8: Dysfunctional phones HIT 200 CPSE Page 19


3.3: Field work 3.3.1: E.M.A According to EMA, the government has not granted them permission to license any probable

means of disposing waste therefore electronic waste is not allowed to be dumped legally in any

places. Because of this reason many organizations which have appealed to EMA on several

occasions to be granted such a license have been denied the license. The result is that

organizations are holding on to the large masses of dysfunctional electronic gadgets including

the Harare Institute of Technology among other universities and industries. According to EMA,

the government plans to start shipping any electronic gadget which would have become

dysfunctional to China and South Africa, which is going to be expensive for the country and

divert funds which could have been used for some other necessary or helpful development in

the country. 3.3.2: Zimstat

Zimstat books were not up to date for e-waste statistics which includes the amount of electronic

gadgets being imported, amount which is locally generated and rate of e-waste being disposed.

However from this research, statistical value was calculated using the sampling method (in

which values from dumpsites, school departments, interviews from domestic users and life

expectances of electronic gadgets were used) and statistical values of the African countries to

get an amount of 30 000 tons per annum of e-waste. 3.3.3: Mbare magaba

A visit to Mbare Magaba illegal waste dump in Harare led to a discovery of a range of e-waste

containing material disposed without any effort of metal recovery. It is evident that the waste

is from adjacent households as it contains broken TV, radios, DVDs etc. 3.3.4: Research based on people’s activities to electronic gadgets domestic users:

The research team conducted a survey on 140 households across Zimbabwe using random

sampling. The study focused on the buying and disposal pattern of the electronic products and

to assess the e-waste awareness among domestic users. The survey threw light on the following

aspects: Product usage



Purchase and disposal behavior

Awareness about e-waste, its hazards nature and recycling methods

E-waste collection systems and convenience. 3.4: Results

The survey reflected the following: 1. 2.

Awareness of the toxic substances present in the e- waste

Knowledge of the hazards to human health and the environment 3.5: Materials and experimental procedure 3.5.1: Dissolution 1 of PCBs An experiment was done to determine the metal in PCB Aim: To determine metal compositions in a PCB extract. Objectives:

Selection and preparation of e-scrap.

Dissolution of the metals present in PCB into prepared solution.

To determine the mass composition of the metals. Determining the power consumed by equipment for the experiment.

Apparatus:

PCB containment gadgets, balance, pliers, nitric acid, magnesium nitrate, magnetic stirrers,

cloth bag, graphite rod, voltage source, stop watch, distilled water, meter and voltmeter, aqua

regia, Method:

A mass of PCB containing gadget was weighed and cut into small pieces.

4 litters of distilled water was mixed with 400ml nitric acid (HNO3).



300gm Sodium nitrate (Na(NO-3)) was added and stirred by 2 magnetic stirrers.

The PCBs were placed in a cloth bag and a graphite rode was inserted in the bag.

A current of 0-12A, voltage to 15V was passed through while a stop watch was used to

estimate time taken by the process to reach maximum current level.

The stop watch was stopped when the maximum current was achieved.

The remains in the bag were taken out, dried and weighed and the weight loss in the

scrap was calculated.

The current, voltage and time were measured so as to calculate the energy consumed

for dissolution. The experiment was repeated. 3.5.2: Recovery of gold using cyanide leaching and precipitation

Aim; To recover the metals from solution through cyanide leaching and precipitation: Apparatus:

250 ml flask, balance, universal indicator, filter paper, stop watch, lime, sodium cyanide(

NaCN), sodium nitrate (NaNO3 ), silver nitrate ( AgNO3 ), oxalic acid, hydrochloric acid Method: Leaching

A sample of 100 ml of the 99g remaining solution of PCB’s was put in a 250ml flask.

The sample was pulped.0.5g of lime was added to achieve a pulp pH of 10.5, followed

by 1.54g of sodium cyanide.

Mechanical agitation was carried out for 24hours, with regular withdrawal of solution

samples to monitor the dissolution rate and reagent consumption, being replenished to

maintain target levels.

At the end of the leach period, the pulp was filtered and the solution was taken for

precipitation.

The amount of sodium cyanide added = 0.1/100 × 2000 × 0.77

= 1.54g (0.77 is the conversion factor)

The % CaO in solution was determined by titration with oxalic acid. HIT 200 CPSE Page 22


Method: Precipitation

100 ml of the pregnant leach solution at pH of 11.9 was placed in a beaker. The

free oxygen in the leach liquor was removed by heating the solution for an hour

without boiling it.

10g zinc powder was added to the leach liquor in order to allow all the gold

to precipitate out of solution.

The mixture was left for 3 hours in order to precipitate the maximum amount of

gold from the pregnant leach solution.

The precipitation efficiency was improved by addition of a few drops of sodium

(II) ions in the form of sodium nitrate.

The precipitate was filtered out of solution (which looks like grey mud).

The precipitate was washed by a weak hydrochloric solution to remove residual

zinc. The ratio of HCl to H2O was 1:10. 3.5.3: Recovery of metals using aqua regia

Aim: To recover the metals from solution through leaching and precipitation with aqua regia:

Apparatus:

Nitric acid, hydrochloric acid, beaker, fume hood, plate stove, clock, filter paper, measuring

cylinder, Method: Leaching

100ml volume of 1M nitric acid was mixed with 300ml of HCl in a beaker under a

fume hood.

The mixture was boiled until the colorless liquid had changed color to lime.

The hot liquid was then added to 100ml and mixture was then boiled until it turned to

a thick paste.

100ml HCl diluted 1:1 with water was added to the paste and boiled again for

30minutes.



The solution was allowed to stand for 2 hours and then filtered and leach pregnant

solution was then taken for precipitation. Method: Precipitation Sodium metabisulphite:

100ml of Sodium metabisulphite solution was diluted with 20ml of distilled water in

order to remove the excess HNO3, and boiled for 20minutes.

An excess amount of 15g sodium metabisulphite was added to the solution while

stirring until dissolution of the precipitant had stopped.

More sodium metabisulphite was added and a white cloud produced; which was an

indication of more gold precipitating.

The mixture was left to cool and mixed in order to precipitate all the gold out of

solution.

The solution was decanted and the residue which looks like black mud was smelted

with borax flux at 1200°C in a furnace. Ferrous sulphate:

10g of ferrous sulphate powder was added to 100 ml of the leach pregnant solution.

2ml oxalic acid was added to the solution to enhance the precipitation process.

A precipitate was formed and more ferrous sulphate was added until sulphur dioxide

(SO2) odour was produced which was an indication that precipitation was complete.

The solution was allowed to stand overnight so all the gold can be settled at the bottom.

The upper precipitant was then filtered and melted with flux.



CHAPTER 4: EXPERIMENTAL RESULTS AND ANALYSES

4.1: Survey results

A social survey was conducted with regards to waste dumping. Various approaches in

collection were proposed by the communities and were put into regard. Three feasible

alternatives were listed for the people to dump their waste:

Door-to-door type of collection system, where a mobile vehicle would collect the e-

waste right from the doorstep;

Stationary collection points and the people bring their wastes to the points. The

stationary system was of three types: Temporary collection center, Permanent

collection center, non- profit collection center;

Mobile collection system, where in a vehicle would come to the central part of an area

on certain days and people have to take their e-waste to that point to dispose. These

vehicles would operate either in milk runs or in specific location coverage;



4.2: Results for dissolution 1 of PCBs

Weight of PCB before Dissolution=160g

Table 4 below shows results from the dissolution experiment.

Table 4: Dissolution 1 results TIME (Minutes) VOLTAGE (Volts) CURRENT (amp) HNO3 ADDED IN (ml)

0 9.92 7.01 25

15 9.02 9.03 -

35 7.67 8.90 -

50 9.68 9.23 -

65 7.73 9.00 50

80 7.41 8.98 50

95 7.02 7.97 50

105 6.78 7.99 100

125 6.51 7.99 100

145 6.33 7.96 100

175 6.07 7.96 100

220 5.80 7.93 200

270 5.38 7.92 200

295 5.34 7.85 -

Weight of PCB after Dissolution = 102g pH = 1



4.3: Results for dissolution 2 of PCBs Weight of PCB before Dissolution=160g The table below shows results from the second experiment. Table 5: Dissolution 2 results TIME (minutes) VOLTAGE (Volts) CURRENT (amp) HNO3 ADDED IN (ml)

0 9.60 9.98 -

15 9.54 9.90 100

40 8.93 9.86 100

55 8.97 9.86 50

75 8.55 9.85 50

120 7.92 9.83 100

135 8.04 9.82 50

150 7.90 9.82 50

165 7.90 9.80 50

180 7.83 9.80 50

195 7.68 9.79 50

210 7.79 9.80 50

225 7.57 9.80 -

Weight of PCB after Dissolution =96g pH = 3 Reactions which took place



HNO3 H+ + NO3- …….. (1). NaNO3 Na+ + NO3- …….. (2). Na+ + H2O NaOH + H2 …….. (3). H2O H+ + OH- …….. (4). H2O + 2OH- ½ O2 + H+ .…….. (5). For Copper: Cu + NO3- Cu (NO3)2 (goes in solution) + 2e- …….. (6) 4.4: Calculations

For experiment 1 average voltage =total voltage(vt) ÷number of time recoded Vt = (9.92+9.02+7.67+9.68+7.73+7.41+7.02+6.78+6.51+6.33+6.07+5.80+5.38+5.34) V =100.66 volts Number of times = 14 Average voltage = 100.66 ÷ 14 = 7.19 V Average current = total current (at) ÷ number of time recorded

AT = (7.01+9.03+ 8.90 +9.23+ 9.00+8.98+7.97+7.99+7.99+7.96+7.96+7.93+7.92+7.85)

= 115.72 Average current (Aav) = 115.72÷1= 8.27 A Power calculations

POWER = VT ×AT

For experiment 1 8.27 ×7.19 = 59.4613 W



Power in kWhr = (59.4613/1000)*295/60 = 0.292kwhr For experiment 2 Vav = (9.6+9.54+8.93+8.97+8.55+7.92+8.04+7.9+7.9+7.83+7.68+7.79+7.57)/13 = 8.325V Av Current = (9.98+9.9+9.86+9.86+9.85+9.83+9.82+9.82+9.80+9.80+9.79+9.8+9.8)/13

= 9.839 A Power (Kwhr) = av current * Vav * time =9.839*8.325*225/(60*1000) kwhr =0.307 kwhr Average power for the 2 experiments = 0.2995kwhr Table 6: Calculations of power consumption in dissolution experiment 2 Exp

number

Initial mass of

scrap (g)

Vaverage(Volts) Aaverage(Amp) Time(min) Power(kwhr)

1 160 7.19 8.27 295 0.292

2 158 8.325 9.839 225 0.307

% of metal content is. P= (mass before electrolysis - mass after electrolysis)/ mass before

electrolysis * 100 For experiment 1: % = (160-102)/99 *100 = 38.12% For experiment 2: %= (158-94)/94 *100 = 39.24% Average composition for the experiments = (38.12+39.24)/2 = 37.75%


Mas

s of

NaC

N (g

)


4.5: Results for cyanide leaching and precipitation

Table 7: Leaching solution preparation and reagents consumption Time % KCN NaCN Added (g)

11:00 - 1.54

12:00 0.05 1.23

13:00 0.08 1.39

14:00 0.09 0.77

08:30 0.04 1.39

09:30 0.08 1.08

10:30 0.09 0.62

11:00 0.10 Finished 2

1.5

1

0.5

0

1 2 3 4 22 23 24 Time (Hrs)

Figure 9: Mass of NaCN consumed with time



4.6: Precipitation

Table 8: Amount of gold recovered from precipitation at pH 11.8 Precipitant before precipitation (gm) after precipitation (gm) % gold extracted

Zinc 0.198 0.002 98.99

Aluminum 0.198 0,096 51.51

The amount of gold precipitated by zinc powder = (0.198-0.002)/0.198)×100% = 98.99% The amount of gold precipitated by aluminium powder = (0.198-0.096)/19.8)×100% = 51.51% Table 9: Amount of gold after precipitation at pH 12.4 Precipitant before precipitation (gm) after precipitation (gm) % gold extracted

Zinc 0.198 0.002 98.99

Aluminum 0.198 0.027 86.36

4.7: Experiment 4: Aqua regia leaching and precipitation

Table 10: Amount of gold recovered by precipitation Precipitant gold in leach liquor

before precipitation (gm)

gold in barren solution

after precipitation (gm)

% gold extracted

Na2S2O5 0,161 0.028 82.61

Ferrous sulphate 0.161 0.097 39.75

Amount of gold precipitated by Na2S2O5 = (0.133/0.161)×100% = 82.61% Amount of gold precipitated by ferrous sulphate = (0,064/0.161)×100% = 39.75%



Table 11: Amount of gold left in solution after precipitation Precipitant Before precipitation (gm) after precipitation gm) %Gold extracted

NaBH4 on Zn 0.160 0.013 91.88

NaBH4 on Al 0.160 0.060 62.50

Amount of gold precipitated with NaBH4 on Zn = (0.147/0.160)×100% = 91.88% Amount of gold precipitated with NaBH4 on Al = (0.100/0.160)×100% = 62.50% Table 12: Gold precipitated recovered by smelting using borax flux Leach solution Precipitating agent Pregnant leach (ml) Mass Au (mg)

Thiosulphate NaBH4 on Zn 100 0.5823

Aqua regia Na2S2O5 100 0.6021

Cyanide Zn 100 0.6001

4.8: Analysis of results

Metals occupy 37.75% of the e-scrape and the power consumed to separate them is

0.2995 Kwhr.

Using cyanide as the lixiviant dissolved very high amounts of gold into solution. The

leaching process was allowed a longer residence time of 24 hours; zinc powder proved

to be a better precipitating agent than aluminium. Zinc powder precipitated 98.99% of

the gold whereas aluminium powder precipitated 51.51% of the gold at pH 11.8.

The pH was adjusted to 12.4 by adding sodium carbonate. There was a remarkable

increase in the amount of gold precipitated by aluminium by a factor of 0.628 to

83.86%. The gold precipitated by zinc was unaffected by increasing the pH. A

hydroxide layer is formed on the surface of the aluminium which passivates the

precipitation process on lower pH.


FEASIBILITY STUDY OF RECOVERING PRECIOUS METALS FROM E-WASTE 2014 The zinc precipitated pregnant solution gave 0.6001g of gold. A tonne of PCBs

therefore can yield 12g of gold. Therefore total amount of gold recovered is 75% .

On thiosulphate leaching sodium borohydride (NaBH4) on zinc proved to be a better

precipitating agent than NaBH4 on aluminium. The cause for the lower recovery was

centered on passivation of aluminium on lower pH (<13) by forming a hydroxide layer.

Thiosulphate dissolved less gold than cyanide into solution. The reason for lower

recovery is lower residence times and also passivation by cupric sulphide formed by

the reaction between cupric ions and thiosulphate ions and or the oxidation of cuprous

thiosulphate complex ions. Above 100ºC cupric sulphide adhering to the gold surface

becomes easily removed and the dissolution of gold remarkably increases. The total

amount of gold that can be recovered by this process was found to be 72.8%.

Aqua regia proved to be a better lixiviant than thiosulphate by 0.625%. Sodium

metabisulphite (Na2S2O5) precipitated more gold from leach liquor than ferrous

sulphate. Sodium metabisulphite precipitated twice the amount of gold from solution

as compared to ferrous sulphate .Total amount of gold that can be recovered by this

process was found to be 75.3%.

Table 13: Comparison of different lixiviants Lixiviant Gold leached (ppm)

Thiosulphate 16.0

Aqua regia 16.1

Cyanide 19.8


Am

ount

leac

hed


20

18

16

14

12

10

8

6

4

2

0 Thiosulphate Aqua regia cyanide

Lixiviant

Figure 10: Amount of gold leached by different leaching agents

The order of dissolution of gold from the highest to the lowest was cyanide, aqua regia, and

thiosulphate. HIT 200 CPSE Page 34


%Au recovered Cyanide Zn

cyanide(pH 11.8) 0 Al

Cyanide(pH 12.4) 0

39.75 0 82.61

Al Thiosulphate

0 NaBH4 on Zn Thiosulphate

62.5 98.99 NaBH4 on Al Aqua regia

91.88 86.36

51.51 Na2S2O5

Figure 11: Amount of gold precipitated with different precipitating agents



CHAPTER 5: PROCESS DESIGN

5.0: Introduction

This chapter is aimed at highlighting the process designed with the aid of a process flow

diagram, material balance and energy balance, giving a full description of the process being

undertaken. 5.1: Block flow diagram

PCB feed

PCB sampling PCB dismantling

Unrecovered metals

zinc

Figure 12: Block flow diagram

Feromagnetic

materials

Grinding Magnetic separator

Elecrostatic Eddy curent separator separator

Non metals Non metals

cyanide Na2S2O5

Gold leaching Silver leaching

Gold precipitation Silver precipitation

Un chloride recovered

metals

Gold to Silver to smelter smelter

water

Used water

Washing and drying

Sulphiric acid

Copper leaching

NaCl

Copper precipitation

Copper to smelter



5.2: Mass balance Material balances are the basis of process design. A material balance taken over the complete

process was used to determine the quantities of raw materials required and products produced.

Balances over individual process units set the process stream flows and compositions.

Fig 13 below shows the block flow diagram for the process with the mass balances of the

processes PCB feed

PCB sampling 160 g 160 g

PCB dismantling Grinding 160 g

130 g

Elecrostatic separator

70 g

Non metals

5g cyanide 83 g

To waste t reatment

Gold leaching

Feromagnetic materials

9 g

30 g Magnetic separator

40 g

Eddy curent separator

60 g

20 g

Non metals

10 g Na2S2O5

45 g sln

Silver leaching

water

80% wt(48.8g) 81.6% wt(49.8)

dirty water

Washing and drying

61 g

60 g

Sulphiric 55 g acid

Copper leaching 20g

H2SO4 25 g

2 g sln

1 g zinc Gold precipitation

35g sln

2.982 g waste

20 g 40 gsln sln

sln 10g NaCl

Copper precipitation

Silver precipitation

2 g chloride

Copper to 0.0108 g Gold to

smelter 7 g Silver to 15 g

smelter smelter

Figure 13: Mass balance chart

5.3: General mass balance equation

The general conservation equation for the process system can be written as : INPUT + GENERATION - OUTPUT - CONSUMPTION = ACCUMULATION



Under steady state conditions MASS INPUT = MASS OUTPUT. 5.4: Overall mass balance

This is a material balance calculated over the whole process. In calculating the overall material

balance equation Calculating overall material balance for the entire process can be ambiguous

therefore system boundaries are going to be applied and firstly the material balance on unit

operation are going to be carried out then it is integrated to the overall into the overall material

balance.

1. Balance at electronic separator

BASIS = 160 g OVERALL BALANCE: INPUT = OUTPUT

INPUT

2. Separation unit:

160 g metals& non metals

PROCESS OUTPUT

SEPERATION 61g metals

99g Non metals 3. Washing and drying: solution output = 61g +0.8(61g) - 49.8 = 60g washed metals



4. Copper precipitation: output = 25g +10 - 25g =15 g copper 5. Silver precipitation: output = 40g +2g- 35g = 7g silver 7. Gold precipitator Output = 2g +1g- 2.982 =0.0108g gold

In order to match an annual feed of 20 000 tones, the laboratory experiment have a scaling

factor of 125exp6. SCALING FACTOR = 20000 000kg/ 0.16kg = 125exp6

The results for the mass balances are shown in Table 14 below for an annual production. Table 14: Scaling up of mass balance Input / year in tonnes Output /year in tonnes

E-WASTE 20000 COPPER 1875

H2SO4 2500 GOLD 1.35

NA2S3O2 1250 SILVER 875

CYANIDE 625

NaCl 1250

Zinc 125

Chloride 250

5.5: Energy Balance

According to the first law of thermodynamics the conservation of energy is described by the

equation:

Energy out = Energy in + Generation - Consumption - Accumulation

For the electrical equipment, power was calculated from the relationship between the voltage

across the equipment and electrical current through them. The calculated power consumed is

tabulated in Table 15 below Energy = voltage * current * time taken for the process



Table 15: Power consumption EQUIPMENT POWER KWh

Shredder 125000

Crusher 1 65000

Crusher 2 10220

Electrostatic separator 2000

Magnetic separator 202

Concentrator 400

Total 202822

Scaling up the power used for experiment 0.292 * 125 000 = 36500

The recovering of metals from e-waste has its own energy balance and so is the leaching,

precipitation and the generation process. Following the conservation of energy the following

equation applies 5.5.1: Overall balance for process (open system)

Based on the Principle of Conservation of Energy and taking a basis of calculation of 1 hour, ΔH + ΔK + ΔP = Q + W ASSUMPTIONS

At steady state (ΔK=0), no change in elevation(ΔP=0)

Total energy input=202822kWh + Q = ΔHtot

Enthalpy change of reaction = enthalpy change of formation ofproducts - enthalpy change of

formation of reactants ΔHtot (reaction) = ΔHf(Cu) + ΔHf(Pb)+ΔHf(Ag)+ΔHf(Au)-( ΔHf(Cu(NO3)2) +

ΔHf(Pb(NO3)2) + ΔHf(Ag(NO3)) + f(Au(OH)3)) HIT 200 CPSE Page 40


=-(-73.1kcal/kmol / Mr(Cu(NO3)2)-106.88kcal/kmol /Mr(Pb(NO3)2) -29.4kcal/kmol /

Mr(Ag(NO3)) -100.6kcal/kmol /Mr(Au(OH)3)) =1219.45 kcal/kg

=3.148kJ/kcal x 1219 kcal/kg

=3838.8 kJ/kg (Crushed PCBs)

5.6.: Process flow diagram

Fig 14 below shows the diagram of the process flow diagram for the whole process starting

from the crushing of a PCB to the metals recovered. PCB feed

Shredder

Dust <0.075mm

Magnetic separator

Hydro Cyclone

5X5 cm

Crusher

1-2mm

Middling

Crusher

Non metals

E lectrostatic separator

Magnetic separator

Non metals

Mixer

Feromagnetic metals

Ferromagnetic metal dust

2M H2SO4

Na2S2O3

Filter

Filter

Filter Copper to smelter

Liquid with non-desired metals

Cementation filter

Silver to s smelter

Cyanide

Filter

Cyanide absorption chamber

Liquid with non-desired metals

Gold to smelter

Figure 14: Process flow chart of the whole process HIT 200 CPSE Page 41


5.7: Process description This section aims to highlight the process taking place, as designed in the process flow diagram. 5.7.1: PCB sampling and dismantling

The process involve shredding of the PCBs into 5x5 cm plates followed by crushing into an

average diameter of 1.5 mm. this is done as to increase the surface area when processes such

as leaching are carried out. Hence the process of PCB dismantling is particle size reduction. 5.7.2: Separation techniques Three techniques for separation of PCB particles into their different components based on their

properties were employed to get a high percentage of the separation yield 5.7.2.1: Electrostatic separator An electrostatic separator is a device for separating particles by mass in a low energy charged

beam. Generally, electrostatic charges are used to attract or repel differently charged crushed

PCB material. The same electrostatic separator can use force of attraction to sort the PCB

particles, conducting PCB particles stick to an oppositely-charged object, such as a metal drum,

thereby separating them from the particle mixture. When this type of beneficiation uses

repelling force, it is normally employed to change the trajectory of falling objects to sort them

into different places. This way, when a mixture of PCB particles falls past a repelling object,

the particles with the correct charge fall away from the other particles when they are repelled

by the similarly charged object. An electrostatic separator is shown in Fig:15. HIT 200 CPSE Page 42


(www.alibaba.com/product-detail/Ht-Roll-Electrostatic_12224081/shoimage.html )

Figure 15: Electrostatic separator

5.7.2.2: Eddy current separator An eddy current separator (shown in Fig:16 below) uses a powerful magnetic field to separate

non-ferrous metals from waste after all ferrous metals have been removed previously by some

arrangement of magnets. The device makes use of eddy currents to effect the separation. The

eddy current separator is applied to a conveyor belt carrying a thin layer of mixed e-waste. At

the end of the conveyor belt is an eddy current rotor. Nonferrous metals are thrown forward

from the belt into a product bin, while non-metals simply fall off the belt due to gravity.Eddy

current separators may use a rotating drum with permanent magnets, or may use an

electromagnet depending on the type of separator

( www.compost.css.cornel.edu/MSWFactsheets/msw.fs1.html ) Figure 16: Eddy current separator


http://www.alibaba.com/product-detail/ht-roll-electrostatic_12224081/shoimage.html

http://www.compost.css.cornel.edu/mswfactsheets/msw.fs1.html


5.7.2.3: Magnetic separator Magnetic separation is a process in which magnetically susceptible material is extracted from

a mixture using a magnetic force. In this magnetic separator crushed PCB material was fed

onto a moving belt which passed underneath two pairs of electromagnets under which further

belts ran at right angles to the feed belt. The first pair of electromagnets is weakly magnetized

and serves to draw off any iron particles present. The second pair is strongly magnetized and

attracts the wolframite, which is weakly magnetic. These machines were capable of treating 10

tons of ore a day. This process of separating magnetic substances from the non-magnetic

substances in a mixture with the help of a magnet is called magnetic separation. Fig 17 below

shows a process of magnetic separation.

(www.antohendarto.blogspot.com/2012/02/magnetic-seperator.html)

Figure 17: Magnetic separator 5.7.3: Cyanide absorption chamber

Activated carbon, also called activated charcoal or activated coal, is a form of carbon processed

to be riddled with small, low-volume pores that increase the surface area available for

adsorption or chemical reactions. Due to its high degree of micro porosity, just one gram of

activated carbon has a surface area in excess of 500 m2, as determined by gas adsorption.

Complete cyanide removal is obtained at ambient temperatures by passing pre-aerated

solutions of cyanide at pH 8-9. The capacity and efficiency of the activated carbon is enhanced HIT 200 CPSE Page 44

http://www.antohendarto.blogspot.com/2012/02/magnetic-seperator.html


by adding cupric ions to the solution. This behavior is explained by the preferential adsorption

of Cu (CN) 2- over CN- on activated carbon. Activated carbon absorb up to 7.7 g CN-/kg.C. 5.7.4: Cyanide Treatment: ozone oxidation

Ozone oxidation of cyanide was chosen as the method for treating cyanide. Cyanide oxidation

with ozone is a two-step reaction similar to alkaline chlorination. Ozone is a strong oxidizing

agent with an electrode potential of +1.24. Cyanide is oxidized to cyanate, with ozone reduced

to oxygen per the following equation:

CN- + O3 → CNO- + O2

Then cyanate is hydrolyzed, in the presence of excess ozone, to bicarbonate and nitrogen and

oxidized per the following reaction:

2 CNO- + 3O3 + H2O → 2 HCO3- + N2 + 3O2

The reaction time for complete cyanide oxidation is rapid in a reactor system with 10 to 30

minute retention times being typical. The second-stage reaction is much slower than the first-

stage reaction. The reaction is typically carried out in the pH range of 10-12 where the reaction

rate is relatively constant. Temperature does not influence the reaction rate significantly. To

complete the first reaction requires 1.8 -2.0 lbs of ozone per lb of CN-.

The metal cyanide complexes of cadmium, copper, nickel, zinc and silver are readily destroyed

with ozone. The presence of copper and nickel provide a significant catalytic effect in the stage

one reaction but can reduce the rate of the stage two reaction (oxidation of cyanate). Iron, gold

and cobalt complexes are very stable and are only partially oxidized, unless a suitable catalyst

is added. Ultraviolet light (UV oxidation), in combination with ozone, can provide complete

oxidation of these complexes.

UV oxidation, in combination with ozone, can completely oxidize all metal cyanide complexes.

UV oxidation is limited to relatively clear solutions, since waste streams are passed through a

light-transmitting chamber and exposed to intense UV light. UV in combination with ozone

results in the formation of OH• radicals, which are strong oxidizing agents capable of oxidizing

iron cyanide complexes. Suitable light sources emit in the range of 200 to 280 nanometers

(nm). Ozone will absorb in this band. A major advantage UV/ozone oxidation is that no

undesirable byproducts (e.g., ammonia) are generated. HIT 200 CPSE Page 45


5.7.4.1: Advantages of Ozone Oxidation on cyanide treating

Extremely effective against all free and complex cyanides either alone or in

combination with UV light

Does not form any undesirable by products such a chlorinated organics or ammonia

Does not require the purchase, storage or handling of dangerous chemicals on site

Ozone is produced on site from air using an ozone generator

The reaction with ozone does not require high temperatures or pressures

5.8: Process innovation A process innovation is the implementation of a new or significantly improved production

or delivery method. The research managed to come with an innovation in the designing of the

process, the addition of the electrostatic separator will increase the purity levels of our

recovered metals, this is because of the significantly non-metal free PCB material that will be

produced for leaching. Another innovation is the use of activated carbon together with Ozone

in the treating of cyanide. The combined use of these two techniques will ensure that we

produce contaminant free product and also we safe guard the environment against the negative

impacts of cyanide. 5.9: Process control

This highlights the process control strategy for temperature, pH and flow which is incorporated

in the design of the equipment. Different process instrumentation has been suggested for the

equipment. 5.9.1: Process instrumentation and control The plant uses automatic control system because manual operation would necessitate

continuous monitoring of the controlled variable by a human operator and the efficiency of

observation would inevitably fall off with time. Instruments are provided to monitor key

variables during the plant operation.

5.9.2: Control system characteristics

The controller and the final control element are pneumatically operated due to the following

reasons: HIT 200 CPSE Page 46


The pneumatic controller is varying rugged and almost free of maintenance. No much

training is required as compared to electronics basically pneumatic equipment is

simple.

The pneumatic controller appears to be safer in a potentially explosive atmosphere

which is often present in acid related operations.

Transmission distances are short. Pneumatic and electronic transmission system is

generally equal up to about 250 to 300 feet. Above this distance, electronic systems

begin to offer savings.

5.9.2.1: Mode of control algorithm

PID control

Cascade control

5.9.3: Alarms, safety trips and interlocks

Alarms are to be incorporated to alert operators of serious, and potentially hazardous,

deviations in process conditions. Key instruments are fitted with switches and relays to operate

audible and visual alarms on the control panels.

Safety trip will be incorporated in all control loops involved in the process. Where it is

necessary to follow the fixed sequence of operations for example, during a plant start-up and

shut down, or in batch operations as in this case, interlocks are to be included to prevent

operators deviating from the required sequence.

5.9.4: Process control of the leach reactor

Control strategy has been developed for the following parameters:-

Temperature

pH



5.9.4.1: Temperature control system The reaction in the leach reactor is exothermic and temperature of 600C is required for the

effectiveness of the reaction. The temperature of the reactor can reach 950C if not controlled

and this will reduce recovery efficiency in the leach reactor, therefore the objective of the

control system is to control the reactor temperature at 600C, a ±30C deviation will be tolerated.

Cascade control is going to be used; the primary controller is the reactor temperature coolant

temperature controller. It measures the reactor temperature, compares it to the set point, and

computes an output, which is the set point for the coolant flow rate controller. This secondary

controller compares the set point to the coolant temperature measurement and adjusts the valve.

The principal advantage of cascade control is that the secondary measurement (jacket

temperature) is located closer to a potential disturbance in order to improve the closed-loop

response.

The reactor temperature can be influenced by changes in disturbance variables such as feed

rate or feed temperature; a feedback controller is employed to compensate for such disturbances

by adjusting a valve on the coolant flow to the reactor jacket. In a situation were an increase

occurs in the coolant temperature as a result of changes in the plant coolant system, this will

cause a change in the reactor temperature measurement. With a cascade control in place, the

jacket temperature is measured, and an error signal is sent from this point to the coolant control

valve; this reduces coolant flow, maintaining the heat transfer rate to the reactor at a constant

level and rejecting the disturbance. The cascade control configuration will also adjust the

setting of the coolant control valve when an error occurs in reactor temperature. 5.9.4.2: PH control systems

The pH control system measures the pH of the solution and controls the addition of a

neutralizing agent (on demand) to maintain the solution at the pH of neutrality, or within certain

acceptable limits. It is, in effect, a continuous titration. These pH control systems are

highly varied, and design depends on such factors as flow, acid or base strength or

variability of strength, method of adding neutralizing agent, accuracy of control (i.e., limits to

which pH must be held), and physical and other requirements. A cascade control is used in the

control of pH. The reactor will have sensing pH electrodes inside the reactor. The pH

electrodes are the measuring devices in this setup. In a situation a disturbance happens

inside the reactor, the measurement produced will be sent to the transducer and in turn a signal HIT 200 CPSE Page 48


will be sent to the pH controller. The pH controller will process the deviation from the required

range of pH and necessary control measure will be sent either to add acid or the buffer

solution. A disturbance can be as a result of change in the strength of acid being fed into the

reactor as a reactant. The pH in the supply pipe will be measured and an error signal will be

sent from the pipe to the control valve, thereby maintain the required pH range in the reactor

and rejecting the disturbance.

For the control to be effective a hold-up time of 5 minutes or more is required and also adequate

mixing and agitation, otherwise, the sensing pH electrodes will detect an incorrect pH

and continue To call for additional reagent after the correct amount has been added. The

result of insufficient mixing is excessive cycling and poor pH control. As a rule of thumb,

turnover (mixing) time should be less than 20% of holdup time. If, for example, holdup

time is 10 minutes, turnover should be less than 2 minutes.



CHAPTER 6: ECONOMIC ANALYSIS

6.1 Introduction

For the commercial success of the project, financing estimation of project cost (fixed cost and

working capital), estimation of manufacturing unit cost, and calculation of annual net cash

flows were done to determine the economic feasibility of the project using profitability

estimators such as payback period (PP), breakeven point (BEP), return on investment.

Capital investments consisting of fixed capital and working capital required for the process is $

15 000 000. Capital investment = fixed capital + working capital

The fixed capital cost (money needed to supply the necessary manufacturing and plant

facilities) comprises of direct and indirect cost. The direct costs and indirect costs for the

processes are given in table 16 and 17 as shown below respectively, with table 18 showing the

equipment costs. Table 16: Direct costs for the recycling process

Description Cost USD $

Equipment 3 590 000.00

Land 1 500 000.00

Buildings 1 500 000.00

Vehicles 2 000 000.00

Instrumentation and control 410 000.00

Piping and electrical equipment 1 000 000.00

Services facilities 1 000 000.00

Total 11 000 000.00 HIT 200 CPSE Page 50


Table 17: Indirect costs

INDIRECT COST COST USD $

Engineering and supervision 8 00 000.00

Construction expenses 1 700 000.00

Contingency 5 00 000.00

Total indirect costs 3 000 000.00

Fixed capital = direct cost + indirect cost

= $ 11 000 000 + $ 3 000 000

= $ 14 000 000.00 Table 18: Summary of equipment costs ( www.matche.com/equipcost)

Description Quantity Cost US$

Filter 10 1400 000.00

Dryer 8 200 000.00

Conveyor belt 20 30 000.00

Optional vibrating feeder 10 60 000.00

Reactor (mixer/settler) 8 1600 000.00

Screening machine 7 50 000.00

Eddy current separator 2 80 000.00

Magnetic Separator 2 70 000.00

Electrostatic separator 2 80 000.00

Total 3 590 000.00

Working capital is needed for the operation of the plant. The working capital for the recycling

process is $ 1 000 000. Capital investment = fixed capital + working capital = $ 10 500 000.00 Sales represent the revenue of the recycling process.


http://www.matche.com/equipcost/


6.2: Sales calculations Feed stock of the process = 20 000 tones / yr Table 19: Metal prices (www.mining.com/market-data) 28 February 2012 Metal Price USD Amount recovered /year

/oz *exp6

Total value x

USD

Gold 380/oz (29.2% purity) 66.14 16 500 051

Silver 20/oz ( 15% pure) 0.048 82 370 12

Copper 3.2/oz (60% purity) 30.86 130 092

Total sales of metals = $ 24 867 155 6.3: Total cost

Total costs are the costs for operating the plant and selling the product. Total cost comprises

manufacturing costs and general expenses. For this process it was calculated on an annual basis.

Annual basis is the best calculation because it takes into consideration the seasonal variations,

equipment operation and smoothens out peaks and troughs in production volumes.

Total Cost = Manufacturing cost + general expenses + plant overheads

Manufacturing cost is divided into direct/variable and indirect/fixed cost.

Table 20: Direct manufacturing costs Component description Cost

Catalyst 1 00 000.00

Transport expenses 900 000.00

Operating labor 1 500 000.00

Power and plant maintenance 2 500 000.00

Total 5 000 000.00

Fixed manufacturing costs are expenses which remain practically constant from year to year

and do not change with production rate. These include depreciation, loan interests and

insurance.


http://www.mining.com/market-data/


Depreciation is to be considered as a loss of value of fixed assets. Equipment and vehicles are

estimated to have a useful life of five years and a salvage value of $ 559 000. D = (V - Vs) / tᵤ

Where D is the depreciation, V is the initial value of the assets, Vs is salvage value and tᵤ is the

useful life. D = (5 590 000 - 559 000)/5 = $ 1 006 200 Table 21: Fixed manufacturing costs Description Cost USD $

Depreciation 1 006 200.00

Insurance 1 500 000.00

Rentals 693 800.00

Total fixed manufacturing costs 3 200 000.00

Table 22: Total manufacturing costs Direct cost 5 000 000.00

Indirect cost 3 200 000.00

Plant overheads 1 200 000.00

Total manufacturing costs 8 400 000.00

General expenses were estimated to be $ 2 000 000.00

TOTAL PRODUCT COST = manufacturing costs + general expenses

= $ 8 400 000 + 2 000 000

= $ 10 400 000 HIT 200 CPSE Page 53


6.4: Profitability evaluation Profit = Sales - Total product cost = $24 867 155 - $ 10 400 000.00 = $14 467 155 Return on investment = profit /investment

= $ 14 467 155/ $ 1500 000.00

= 0.96 Payback period = investment / profit

= $ 1 500 000.00 / $ 14 467 155

= 1.04 years 6.5: Break even analysis Break even analysis is an analysis to determine the point at which revenue received equals the

costs associated with receiving the revenue. The break even chat is shown in fig 18 below Break even = fixed cost / (sales - variable cost) = $ 3 200 000/ ($24 867 155- $ 500 000.00) = 0.339



Break even analysis diagram

Figure 18: Break even chart



CHAPTER 7: CONCLUSION AND RECOMMENDATIONS

7.1: Conclusion Since metals have been recovered through a profitable and highly efficient process,

burning of e-waste in open environment or uncontrolled burning is reduced.

The process and conservation of the limited non-renewable resources through

recycling and reducing overall land digging proved successful.

H0 is accepted and we concluded that the project is feasible. 7.2: Recommendations

In order to align with international practice in e-waste management, it is recommended that the

Zimbabwean government should:

Develop specific e-waste legislation which facilitates an enabling environment to make

e-waste a “resource” rather than “waste”;

Develop a legal frame which identifies all the stakeholders and their responsibilities in

the e-waste life cycle;

Create a legal framework which encourages wide spectrum of participants in economic

activities drawn from responsible exploitation of e-waste;

Create a technical committee made up of industrial, commercial and domestic

stakeholder representatives to draft an e-waste policy for economic development;

Create a legal framework which recognizes shared responsibilities by manufacturers,

distributors, collectors, processors, recyclers and consumers in e-waste management;

Accept that e-waste is a form of a resource which can be imported or exported into or

out of Zimbabwe;

Another recommendation is that further studies on the recovery of palladium and lead have to

be carried out to make their recovery processes more economically feasible.



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socially responsible concept to manage e-waste in emerging economies

3. Brandon, N.P., Kelsall, G.H., Schmidt, M.J. and Yin, Q.:(2002) Metal recovery from

electronic scrap by leaching and electrowinning. In: Lagostra, M.C., Veskato, S.,

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electrical and electronic equipment in Korea, Resource. Conserv. Recycle. 50 (4)



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