Hydrometallurgical process for extraction of metals...

Association of Metallurgical Engineers of Serbia
AMES
Scientific paper
UDC: 661.061.34:628.4.043
HYDROMETALLURGICAL PROCESS FOR EXTRACTION OF
METALS FROM ELECTRONIC WASTE-PART I: MATERIAL
CHARACTERIZATION AND PROCESS OPTION SELECTION
Željko Kamberović * , Marija Korać, Dragana Ivšić, Vesna Nikolić,
Milisav Ranitović
Department of Metallurgical Engineering, Faculty of Technology and
Metallurgy, Belgrade, Serbia
Received 11.11.2009
Accepted 28.12.2009.
Abstract
Used electronic equipment became one of the fastest growing waste streams in
the world. In the past two decades recycling of printed circuit boards (PCBs) has been
based on pyrometallurgy, higly polluting recycling technology whic causes a variety of
environmental problems. The most of the contemporary research activities on recovery
of base and precious metals from waste PCBs are focused on hydrometallurgical
techniques as more exact, predictable and easily controlled. In this paper mechanically
pretrated PCBs are leached with nitric acid. Pouring density, percentage of magnetic
fraction, particle size distribution, metal content and leachability are determined using
optical microscopy, atomic absorption spectrometry (AAS), X-ray fluorescent
spectrometry (XRF) and volumetric analysis. Three hydrometallurgical process options
for recycling of copper and precious metals from waste PCBs are proposed and
optimized: the use of selective leachants for recovery of high purity metals (fluoroboric
acid, ammonia-ammonium salt solution), conventional leachants (sulphuric acid,
chloride, cyanide) and eco-friendly leachants (formic acid, potassium persulphate).
Results presented in this paper showed that size reduction process should include
cutting instead of hammer shredding for obtaining suitable shape & granulation and that
for further testing usage of particle size -3 +0.1mm is recommended. Also, Fe magnetic
phase content could be reduced before hydro treatment.
Key words: electronic waste, printed circuit boards, recycling, hydrometallurgy,
copper, precious metals
* Corresponding author: Željko Kamberović kamber@tmf.bg.ac.rs

232 MJoM Vol 15 (4) 2009 p.231-243
Introduction
Fast electronic industry development brought the great benefits in everyday life,
but its consequences are usually ignored or even unknown. Used electronic equipment
became one of the fastest growing waste streams in the world. From 20 to 50 million
tonnes of waste electical and electronic equipment (WEEE, e-waste) are generated each
year, bringing significant risks to human health and the environment [1]. EU legislative
restricts the use of hazardous substances in electrical and electronic equipment (EEE)
(Directive 2002/95/EC) such as: lead, mercury, cadmium, chromium and flame
retardants: polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE)
and also promotes the collection and recycling of such equipment (Directive
2002/96/EC). They have been in implementation since February 2003. Despite rules on
collection and recycling only one third of electrical and electronic waste in the
European Union is reported as appropriately treated and the other two thirds are sent to
landfills and potentially to sub-standard treatment sites in or outside the European
Union. In December 2008 the European Commission proposed to revise the directives
on EEE in order to tackle the fast increasing waste stream of these products [2].
Recycling of printed circuit boards (PCBs), as a key component in the WEEE, in
past two decades have been based on recovery via material smelting. This is highly
polluting, primitive recycling technology that can cause a variety of environmental
problems. It is mostly processed, sometimes illegally, in developing countries, for
instance China, India, Pakistan and some African countries [3,4]. Goosey and Kellner in
their detailed study [5] have defined the existing and potential technologies that might
be used for the recycling of PCBs. They pointed out that metals could be recycled by
mechanical processing, pyrometallurgy, hydrometallurgy, biohydrometallurgy or a
combination of these techniques.
Pyrometallurgy, as traditional method to recover precious and non-ferrous metals
from e-waste, includes different treatments on high temperatures: incineration, melting
etc. Pyrometallurgical processes could not be considered as best available recycling
techniques anymore because some of the PCB componenets, especially plastics and
flame retardants, produce toxic and carcinogenic compounds. The most of the research
activities on recovery of base and precious metals from waste PCBs are focused on
hydrometallurgical techniques for they are more exact, predictable and easily controlled
[6,7].
In recent years the great number of investigations have been conducted in order
to solve the problem of WEEE and develop appropriate recycling techniques. According
to Cui and Zhang [7] recycling of e-waste can be broadly divided into three major steps:
a) disassembly-mechanical pretreatment: selectively removing hazardous and valuble
components for special treatment and it is necessary step for further operations, b)
concentrating: increasing the concentration of desirable materials using mechanical
and/or metallurgical processing and c) refining: metallurgical treatment and purification
of desirable materials.
Hydrometallurgu, i.e. leaching and cementation process in Serbian mine Bor was
first mentioned in 1907 when 200 tons of copper were produced. Since those days till
today copper hydrometallurgy has not mount at Serbia and nearby region [8].
Hydrometallurgical processing consist of: leaching – transfering desirable
components into solution using acides or halides as leaching agents, purification of the

Kamberović et al- Hydrometallurgical process for extraction of metals... 233
leach solution to remove impurities by solvent extraction, adsorption or ion-exchange,
then recovery of base and precious metals from the solution by electrorefining process,
chemical reduction, or crystallization. The most efficient leaching agents are acids, due
to their ability to leach both base and precious metals. Generally, base metals are
leached in nitric acid [9, 10]. The most efficient agent used for solder leach is
fluoroboric acid [11]. Copper is leached by sulphuric acid or aqua regia [12]. Aqua regia
is also used for gold and silver [11], but these metals are usually leached by thiourea or
cyanide [13]. Palladium is leached by hydrochloric acid and sodium chlorate [7].
Biohydrometallurgy is a new, cleaner and one of the most promising ecofriendly
technologies. Biosorption is a process employing a suitable biomass to sorb
heavy metals from aqueous solutions [14]. This is physico-chemical mechanism based
on ion-exchange [15], metal ion surface complexation adsorption or both [16].
Oishi et al. [17] conducted research on recovery of copper from PCBs by
hydrometallurgical techniques. Proposed process consists of leaching, solvent extraction
and electrowinning. In the first stage of research conducted by Veit et al. [12]
mechanical processing was used as comminution followed by size, magnetic and
electrostatic separation. After pretreatment, the fraction with concentrated Cu, Pb and
Sn was dissolved with acids and treated in an electrochemical process in order to
recover the metals separately, especially copper, with two different solutions: aqua regia
and sulphuric acid. Frey and Park [11] performed research for recovery of high purity
precious metals from PCBs using aqua regia as a leachant. The most significant
achievement of this research was synthesis of pure gold nanoparticles.
Sheng and Etsell [9] investigated leaching of gold from computer chips. The first
stage was leaching of base metals with nitric acid and the second, leaching of gold with
aqua regia due to its flexibility, ease and low capital requirement. Non-metallic
materials are also recovered this way, mainly plastic and ceramics. Quinet et al. [18]
carried out bench-scale extraction study on the applicability of economically feasible
hydrometallurgical processing routes to recover silver, gold and palladium from waste
mobile phones. Selective extraction of dissolved metals from solution is very difficult
and demanding process [19].
Experimental
Electronic waste is defined as a mixture of various metals, particularly copper,
aluminum and steel, attached to different types of plastics and ceramics.
The samples for experimental research presented in this paper were milled PCBs
with obtained by mechanical pretreatment of waste computers.
The mechanical pretreatment of end-of-life computers was performed at
SETrade, Belgrade. The first stage was manual disassembling of computers, liberation
of PCBs and removal of the batteries and capacitors. Liberated PCBs were milled in
QZ-decomposer, separating magnetic materials from non magnetic fractions, while
aluminum was manually removed from conveyor belt. Material was then milled in
shredder Meccano Plastica, after which material was not exposed to another magnetic
separation.
Characterization of granulated waste PCBs included determination of following
parameters: pouring density, percentage of magnetic fraction, particle size distribution,

234 MJoM Vol 15 (4) 2009 p.231-243
rate of metal components leachability using optical microscopy, atomic absorption
spectrometry (AAS), X-ray fluorescent spectrometry (XRF) and volumetric analysis.
Also, appropriate hydrometallurgical system for evaluation of metal components and
optimization of process parameters: temperature, time, solid:liquid ratio and mixing
velocity are selected.
Sieve analysis was performed using Taylor type sieves and mass of fractions
obtained after 30 minutes sieving was measured. Percentage of each fraction was
calculateded.
The pouring density of total sample and of each fraction was measured using
Hall flowmeter funnel (ASTM B13). Pouring density of total sample was 889 kg/m 3 .
The sample was subjected to the magnetic separation process using two
permanent magnets each weighing 100g. Percentage of magnetic material content was
5.39%.
Content of metallic and non-metallic components of entire sample as well as for
each fraction was determined by leaching with 50 vol.% HNO3 near to boiling
temperature with agitation followed by filtration after cooling. Metallic fraction is
transferred to liquid. Solid non-metallic residue mass is measured after filtration.
Experimental results are shown in Table 1.
Table 1. Characteristics of PCBs granulated samples
mm Fraction, ρ, kg/m
wt.%
3
Metallic part,
wt.%
5.000 7.07 800 43.84
2.500 37.24 880 50.44
2.000 6.99 830.15 55.47
1.800 8.50 986.33 38.86
1.250 11.68 1235.63 31.57
1.000 5.61 1474.61 48.48
0.800 5.42 1136.59 61.25
0.630 4.81 1022.48 43.95
0.500 1.64 958.63 50.20
0.400 2.75 908.81 44.26
0.315 2.47 794.15 41.31
0.250 1.16 656.74 37.87
0.100 2.82 632.61 35.86
-0.100 1.83 622.05 38.50
Results of the sieve analysis showed that the greatest percent of sample was in
fraction +2.5mm. Metallic part was mostly contained in fraction +0.8 mm.
Figures 1a-f are presenting some of the PCB fractions before and after dissolving
in nitric acid and removal of metallic components.

Kamberović et al- Hydrometallurgical process for extraction of metals... 235
As received After dissolution
a)
c)
e)
Figure1. PCB fractions before and after dissolving in HNO3 a&b) 1.8mm; c&d)
1.0mm; e&f) 0.1mm
b)
d)
f)

236 MJoM Vol 15 (4) 2009 p.231-243
Analysis of chemical composition of granulated PCBs was performed using
volumetric analysis, AAS and XRF spectrometry. Materials used for presented analysis
were both granulated samples and samples after sieve analysis dissolved in 50 vol.%
HNO3.
Volumetric analysis was performed using standard sodium tiosulphate solution
for treatment of samples dissolved in 50 vol.% HNO3. Results showed that copper
content in granulated PCBs was 21.61 wt%. Also, distribution of copper in fractions
was determined by volumetric analysis as presented in Table 2.
Table 2. Distribution of copper in fractions
fraction, mm Cu, wt.%
5.000 21.96
2.500 18.37
2.000 21.81
1.800 13.90
1.250 17.82
1.000 22.75
0.800 26.34
0.630 17.53
0.500 24.26
0.400 20.22
0.315 15.08
0.250 11.16
0.100 11.45
-0.100 11.47
Presented results show that copper is mostly concentrated in fraction +0.8 mm.
AAS was used for analyzing solutions of each fraction, obtained by dissolving in
50 vol.% HNO3, in order to determine content of Cu, Zn, Fe, Ni, Pb. It was performed
by Perkin Elmer 4000 spectometer calibrated with standard solutions for each measured
metal. Results of experimental analysis are shown in Table 3.

Kamberović et al- Hydrometallurgical process for extraction of metals... 237
Table 3. Chemical composition of WPCBs each fraction in wt.%
mm Cu Zn Ni Fe Pb
5.000 11.06 1.89 1.79 5.99 0.89
2.500 30.50 2.25 1.93 0.18 0.71
2.000 30.24 2.28 1.21 2.28 1.53
1.800 24.14 2.04 0.29 0.13 0.78
1.250 35.31 1.73 1.07 1.20 3.85
1.000 33.38 2.23 0.36 1.22 7.15
0.800 27.62 2.21 0.61 0.51 5.91
0.630 28.99 1.68 0.59 0.88 3.56
0.500 40.42 1.81 0.61 1.45 3.44
0.400 40.16 1.24 0.97 1.30 3.50
0.315 23.17 1.27 0.61 1.68 3.76
0.250 14.44 1.18 0.31 1.77 2.09
0.100 7.87 1.31 0.20 2.36 1.50
-0.100 6.32 2.89 0.58 5.22 2.12
Fraction +5mm contained ~6% of Fe, which means that magnetic separation was
not efficient enough for this size of particles.
XRF spectrometry was used for direct analysis of granulated PCBs samples.
Characteristic parts like contacts, solders and composites were analysed. XRF analysis
was performed on Skyray EDX 3000. Measurement spots labeled lom-1 to 4 are
presented at Figure 2 and results in Table 4.
Figure 2. Measurement spots for XRF analysis

238 MJoM Vol 15 (4) 2009 p.231-243
Table 4. Results of XRF analysis
Cu Ag Rh Pd Pt Au
Lom 1 96.254 3.746
Lom 2 95.072 4.928
Lom 3 73.121 6.45 2.521 17.943
Lom 3 30.749 14.762 8.806 2.353 43.33
Lom 4 95.03 4.97
XRF analysis showed that metal content varies from sample to sample and it
highly depends on measuring spot.
Based on detailed literature review and presented experimental results, several
process option were selected as an appropriate hydrometallurgical process for extraction
of metals from electronic waste was.
Process option 1-The use of selective leachants and recovery of high purity
metals from PCBs
This process option involves four main stages:
1. mechanical pre treatment that includes shredding, magnetic separation,
eddy current separation and classification [11],
2. solder leach with fluoroboric acid and Ti(IV) ion as oxidizing agent
[20],
3. recovery of copper that includes leaching with ammonia-ammonium
salt solution, purification by solvent extraction with organic LIX 26 and
electrowinning [17]
4. recovery of high purity precious metals (Au, Ag ang Pd) using aqua
regia [11].
Schematic preview of process option 1 is presented in Figure 3.

Kamberović et al- Hydrometallurgical process for extraction of metals... 239
Non metalic
Electronic Scrap
(General composition:
Cu, Al, Fe, Sn, Pb, Zn, Ni, Ag, Au, Pd + non metallic
Shredding
Magnetic & Eddy
Current separation
Residue: about 90 wt.% of the total
(Cu, Sn, Pb, Zn, Ni, Ag, Au, Pd + non metallic
24h, 25 C
Solder leach
(HBF4 )
Residue: about18 % of the total
(Cu, Zn, Ni, Ag, Au, Pd)
Copper leach
[Cu(II)/NH3/NH4 + ]
Residue: about 2 wt.% of the total
(Zn, Ni, Ag, Au, Pd)
Recovery of precious
metals
Separation of nickel and
zinc
solution
Iron/steel fraction
aluminum fraction
Solder recovery:
electrowinning
solder: 7 wt.% of the total
Sn: 4.2 wt.%
Pb: 2.8 wt.%
solution Copper recovery:
electrowinning
16% of the total
Leaching
Solvent
Extraction
Electrowinning
Figure 3. The recycling process of metals contained in PCB waste
PCB: ground
Solution:Cu(II)/NH3/NH4 +
Duration: 24h, 25°C
Process option 2- The use of conventional leachants for recovery of metals from
waste PCBs
This process option represents bench-scale method for extraction and recovery of
copper and precious metals from waste PCBs. After comminution, material was
subjected to serial of hydrometallurgical processing routes: sulphuric acid leaching and
precipitation for Cu recovery; chloride leaching followed by cementation for Pd, Ag, Au
and Cu recovery and cyanidation and activated carbon adsorption for recovery of Au
and Ag. The proposed flowsheet is presented in Figure 4.

240 MJoM Vol 15 (4) 2009 p.231-243
Figure 4. Proposed flowsheet for the recovery of precious metals from WPCBs [18]
Process option 3- The use of green leachants for recovery of metals from waste
PCBs
This process option is particulary based on recovery of gold from electronic
waste using an “eco-friendly” or “green” reagents. After communition, non-toxic
reagents formic acid and potassium persulphate are used for Au leaching at boiling
temperature. Base metals, obtained as by-products, in a further steps could be recoverd
by electrowining. Gold is recoverd by melting. This process option is presented in
Figure 5.

Kamberović et al- Hydrometallurgical process for extraction of metals... 241
Fig. 5. Flow sheet of gold recovery from gold-plated PCBs (GPCB), gold-coated glass
bangles (GCGB) and gold-coated mirrors (GCM)

242 MJoM Vol 15 (4) 2009 p.231-243
Conclusion
On the basis of experimental results it can be concluded that properties of
investigated material is in accordance with literature and it could be a representative for
selection of proper hydrometallurgical recycling technique. AAS chemical analysis has
shown that fraction above 5 mm contained high amount of Fe and should be avoided by
more efficient magnetic separation. Also, -0.1 mm fracton can cause various difficulties
in process, great loses due to large content of metals in this fraction and decreased
leachability.
Final selection of the process which could be applied for further analysis
depends on input materials characteristics. There is no completely green option.
Selection of suitable hydrometallurgical process highly depend on leaching tests and
techno-economical analysis and possible solution for electronic waste lies in
combination of proposed process options.
Literature
[1] S. Herat, International regulations and treaties on electronic waste (e-waste),
International Journal of Environmental Engineering, 1 (4), 2009, 335 - 351
[2] Recast of the WEEE and RoHS Directives proposed in 2008,
http://ec.europa.eu/environment/waste/weee/index_en.htm
[3] Basel Action Network and Silicon Valley Toxics Coalition, Exporting Harm:
The High-Tech Trashing of Asia, Seattle and San Jose, 2002
[4] Carroll, High-Tech Trash, National Geographic Magazine Online, 2002,
http://ngm.nationalgeographic.com/ngm/2008-01/high-tech-trash/carrolltext.html
[5] M. Goosey, R. Kellner, A Scoping study end-of-life printed circuit boards,
Intellect and the Department of Trade and Industry, Makati City, 2002
[6] J. C. Lee, H. T. Song, J. M. Yoo, Present status of the recycling of waste
electrical and electronic equipment in Korea, Resources, Conservation and
Recycling 50 (4), 2007, 380–397
[7] J. Cui, L. Zhang, Metallurgical recovery of metals from electronic waste: A
review, Journal of Hazardous Materials, 158 (2-3), 2008, 228–256
[8] Ž. Kamberović, D. Sinadinović, M. Sokić, M. Korać, Hydrometallurgical
treatment of refractory and polymetallic copper ores, V th Congress of the
Metallurgists of Macedonia, 17-20 septembar, Ohrid, Makedonija, 2008, IL-02-E
[9] P.P. Sheng, T.H. Etsell, Recovery of gold from computer circuit board scrap
using aqua regia, Waste Management and Research, 25 (4), 2007, 380–383
[10] R. Vračar, Vučković N., Kamberović Ž., Leaching of copper(I) sulphide by
sulphuric acid solution with addition of sodium nitrate, Hydrometallurgy,
Elsevier, vol 70/1-3 (2003) 143 - 151
[11] Y. J. Park, D. Fray, Recovery of high purity precious metals from printed circuit
boards, Journal of Hazardous Materials 164 (2-3), 2009, 1152 –1158
[12] H. M. Veit, A. M. Bernardes, J. Z. Ferreira, J. A. Soares Tenório, C. de Fraga
Malfatti, Recovery of copper from printed circuit boards scraps by mechanical

Kamberović et al- Hydrometallurgical process for extraction of metals... 243
processing and electrometallurgy, Journal of Hazardous Materials, 137 (3), 2006,
1704–1709
[13] Ž. Kamberović, D. Sinadinović, M. Korać, Metallurgy of gold and silver (in
Serbian), SIMS, 2007
[14] K. Chojnacka, Biosorption and bioaccumulation – the prospects for practical
applications, Environment International, 2009, Article in Press, Corrected Proof
[15] G. Naja, V. Diniz, B. Volesky, Predicting metal biosorption performance, In:
Proceedings of the16th International Biohydrometallurgy Symposium, S. T. L.
Harrison, D. E. Rawlings, J. Peterson, Eds., Compress Co.: Cape Town, South
Africa, 2005, 553−562
[16] B.C. Qi, C. Aldrich, Biosorption of heavy metals from aqueous solutions with
tobacco dust, Bioresource Technology, 99 (13), 2008, 5595–5601
[17] T. Oishi, K. Koyama, S. Alam, M. Tanaka, J. C. Lee, Recovery of high purity
copper cathode from printed circuit boards using ammoniacal sulphate or
chloride solutions, Hydrometallurgy 89 (1-2), 2007, 82–88
[18] P. Quinet, J. Proost, A. Van Lierde, Recovery of precious metals from electronic
scrap by hydrometallurgical processing routes, Minerals and Metallurgical
Processing, 22 (1), 2005, 17–22
[19] J. Pavlović, S.Stopić, B.Friedrich, Ž. Kamberović, Selective Removal of Heavy
Metals from Metal-bearing Wastewaters in Cascade Line Reactor,
Environmental Science and Pollution Research-ESPR, 7, Vol.14, (2007), 518-
522
[20] Gibson at al. Patent US 6.641.712 B1, 2003, Process for the recovery of tin, tin
alloys or lead alloys from printed circuit boards

Association of Metallurgical Engineers of Serbia
AMES
Scientific paper
UDC: 628.477.6
HYDROMETALLURGICAL PROCESS FOR EXTRACTION OF
METALS FROM ELECTRONIC WASTE-PART II: DEVELOPMENT
OF THE PROCESSES FOR THE RECOVERY OF COPPER FROM
PRINTED CIRCUIT BOARDS (PCB)
Željko Kamberović 1* , Marija Korać 2 , Milisav Ranitović 2
1 Faculty of Technology and Metallurgy, University of Belgrade, Serbia
2 Innovation center of the Faculty of Technology and Metallurgy, Belgrade,
Serbia
Received 13.06.2011
Accepted 15.08.2011
Abstract
Rapid technological development induces increase of generation of used electric
and electronic equipment waste, causing a serious threat to the environment. Waste
printed circuit boards (WPCBs), as the main component of the waste, are significant
source of base and precious metals, especially copper and gold. In recent years, most of
the activities on the recovery of base and precious metals from waste PCBs are focused
on hydrometallurgical techniques as more exact, predictable and easily controlled
compared to conventional pyrometallurgical processes. In this research essential aspects
of the hydrometallurgical processing of waste of electronic and electrical equipment
(WEEE) using sulfuric acid and thiourea leaching are presented. Based on the
developed flow-sheet, both economic feasibility and return on investment for obtained
processing conditions were analyzed. Furthermore, according to this analysis, SuperPro
Designer software was used to develop a preliminary techno-economical assessment of
presented hydrometallurgical process, suggested for application in small mobile plant
addressed to small and medium sized enterprises (SMEs). Following of this paper, the
described process is techno-economically feasible for amount of gold exceeding the
limit value of 500ppm. Payback time is expected in time period from up to 7 years,
depending on two deferent amounts of input waste material, 50kg and 100kg of WEEE
per batch.
Key words: waste printed circuit boards, recycling, hydrometallurgy, copper leaching,
gold leaching, techno-economical assessment
* Corresponding author: Željko Kamberović, kamber@tmf.bg.ac.rs

140 Metalurgija-MJoM Vol 17 (3) 2011 p. 139-149
Introduction
As a result of rapid technical and technological development, waste electric and
electronic equipment (WEEE) is becoming one of the major environmental risks for its
high quantity and toxicity in recent years. In terms of materials and components WEEE
is non-homogeneous and very complex, and the major challenge for recycling
operations is how to respond to poor recovery of metals by mechanical treatment as well
to avoid gas handling problems or hazard gas compounds release using
pirometallurgical process. Printed circuit boards (PCBs), as a key component of WEEE,
can be considered as a significant secondary raw material due to its complex
composition, mainly consisted of plastic, glass, ceramics and metals (copper, aluminum,
iron, zinc, nickel, lead and precious metals). In the past two decades much attention has
been devoted to development of techniques for recycling WEEE, especially copper and
precious metals [1, 2, 3]. The state of the art in recovery of precious metals from
electronic waste highlights two major recycling techniques, such as pyrometallurgical
and hydrometallurgical, both combined with mechanical pre-treatment.
Pyrometallurgical processing including incineration, smelting in a plasma arc furnace or
blast furnace, sintering, melting and reactions in a gas phase at high temperatures has
been a conventional technology for recovery of metals from WEEE [4, 5, 6]. However,
state-of-the-art smelters are highly depended on investments. In the last decade,
attention has been moved from pyrometallurgical to hydrometallurgical process for
recovery of metals from electronic waste [7, 8].
This paper describes essential aspects of the hydrometallurgical processing of
WEEE using sulfuric acid and thiourea leaching. Previous studies, reported by authors
[9, 10] were conducted in order to investigate optimal processing conditions concerning
hydrometallurgical recovery of base and precious metals from WPCBs. In this paper
some results obtained in these studies are also presented. Based on these results,
regarding characterization and development of the hydrometallurgical treatment of
waste material, both economic feasibility and return on investment for obtained
processing conditions were analyzed. Furthermore, this analysis was used in order to
develop a preliminary techno-economical assessment of presented hydrometallurgical
process adopted for use in small mobile plant taking into account limitation of necessary
quantities of waste material as well as investment, addressed to small and medium sized
enterprises (SMEs).
Materials
Material used in presented research is comminuted and mechanically pre-treated
waste PCBs, as described in previous studies by authors [1, 9, 10]. Chemical
composition of two samples was analyzed using atomic absorption spectroscopy, X-ray
fluorescence spectroscopy and, inductively coupled plasma atomic emission
spectroscopy. Obtained results together with literature data are presented in Table 1. In
this paper, fractions (F), 0.071mm< F

Kamberović et al.- Hydrometallurgical process for extraction of metalsi... 141
2mm and -1mm was examined in the range of 100 to 700 rpm. Solution used for testing
was 30 wt. % NaCl, whose density matches the density of H2SO4 solution used for
leaching.
Table 1. Chemical composition of sample of WPCBs [9]
Materials Sample 1 *
Sample 2
%(w/w)
**
Literature data [3]
%(w/w)
%(w/w)
Cu 27.99 25.24 20
Al 0.47 0.69 2
Pb 2.17 2.22 2
Zn 2.01 2.05 1
Ni 1.23 0.93 2
Fe 1.18 0.98 8
Sn 3.26 3.17 4
Au/ppm 440 890 1000
Pt/ppm 57 17 -
Ag/ppm 1490 1907 2000
Pd/ppm 50 47 50
Ceramics 20.41 22.14 max 30%
Plastics 32.07 32.41 max 30%
* WPCBs collected by S.E.Trade d.o.o. Belgrade, fraction –6mm
** WPCBs collected by Institute Mihajlo Pupin, fraction –1+0.071mm
In a first step fraction -2mm was examined. It was shown that the increase of the
stirring rate did not produce any effect on the waste material which remained at the
bottom of the laboratory glass.
In the next step fraction -1mm was examined when the intensification of material
mixing was noticed at 200 rpm. At 300 rpm, all the granulate particles from the
container are raised and caught mixing while floating particles slowly transit into the
solution. Finally, at 600 rpm all particles of the waste materials are fully affected by
mixing.
In the industrial leaching conditions, stirring rate of 600 rpm is relatively high
and could cause great trouble for carrying out of the process of leaching. It is assumed
that with proper solid:liquid ratio, results obtained at 300 rpm will be satisfactory, and
thus this parameter was fixed in the further analysis.
According to experimental set up, reported in a previous study [1, 9,10], leaching
tests were performed in a glass vessel with 15.6 cm in diameter, with a condenser, steel
impeller, oxygen dispersion tube and hydrogen peroxide dozer. Experimental set up is
shown in Figure 1.
Electrowinning (EW) was performed in a rectangular electrolytic cell with
dimensions 100×88×300mm with effective volume 2000 mL made of high density
polypropylene. The cathode material was copper (Cu 99,99%) and anode was lead
antimony alloy (PbSb7).

142 Metalurgija-MJoM Vol 17 (3) 2011 p. 139-149
Fig.1. Experimental apparatus for leaching: 1.Electro-resistant heater; 2.Reaction
glass vessel; 3.Cooler with condenser; 4.Mixer; 5.Oxygen tube; 6.Peroxide dozer;
7.Digital pH and temperature measurement device
Results and discussion
Optimum processing conditions were obtained by variation of different leaching
parameters. Hydrometallurgical extraction of copper from the waste material was
performed using sulfuric acid as leaching agent. Solid residue after copper leaching
step, was leached by thiourea in the presence of ferric ion (Fe2(SO4)3) as an oxidant in
sulfuric acid solution, in order to extract gold. In the case of copper leaching, analysis
was performed for both, laboratory and pilot scale, while gold leaching was tested only
for laboratory scale. According to summarized results, optimum copper and gold
leaching parameters are presented in Table 2.
Table 2. Optimal gold and copper leaching conditions
Parameter
Copper leaching
Gold leaching
Laboratory scale Pilot scale
Acid conc.
H2SO4 conc. 1.5-2M 1.5-2M 10 g dm -3
thiourea conc. / / 20 g dm -3
Oxidants conc.
H2O2 40mL/h 50 kg/t /
O2 16L/h 80 L/kg/h /
Fe 3+ / / 6 g dm -3
Solid-liquid ratio 50-100g/L 150-200g/L 20 % of solid
Temperature 75-80°C 70°C 40°C
Stirring rate >300rpm ~300rpm 600 rpm
Time >5h

Kamberović et al.- Hydrometallurgical process for extraction of metalsi... 143
EW was performed in order to extract metallic copper from leaching solution.
Optimal EW conditions are shown in Table 3, while obtained copper deposit is
illustrated in Figure 2.
Table 3. Optimal EW conditions
Voltage 2.1V
Current 120-200A/m 2
density
Temperature 40ºC
Time 15h
Steering rate 100rpm
Fig.2. Copper deposited on the cathode
According to presented optimal processing parameters, block diagram for
hydrometallurgical recovery of base and precious metals, using selective leaching
agents from WPCBs was developed. Block diagram for hydrometallurgical processing
of WPCBs using sulfuric acid and thiourea leaching is shown on Figure 3.
Fig.3. Block diagram for hydrometallurgical recovery of base and precious metals [9]

144 Metalurgija-MJoM Vol 17 (3) 2011 p. 139-149
Although hydrometallurgy is relatively widely used in base and precious metals
processing plants, the objective of this work was to discuss the possibility of providing a
purely hydrometallurgical alternative to the pyrometalurgical process as more exact,
easily controlled, less expensive, and less subjected to losses for recovery of base and
precious metals from WEEE. On the other hand, by adopting an entirely
hydrometallurgical route for use in small mobile plant, economic benefits for SMEs
may be possible, regarding low capital investment and necessary quantities of waste
material.
Process option investigated in this paper was based on preliminary results carried
out on the pilot scale in the scope of the European project “Innovative
Hydrometallurgical Processes to recover Metals from WEEE including lamp and
batteries – HydroWEEE” (FP 7 – research activities addressed to SMEs). Core objective
of this project was development of suitable multi functional hydrometallurgical process
for recovery of base and precious metals from fluorescent powders coming from CRT
and spent lamps, printed circuit boards, LCD and lithium spent batteries. The
experience and knowledge obtained in the preliminary pilot plant tests gave important
technological indications for the development of the small mobile plant HydroWEEE.
Furthermore results obtained during the activities of project, particularly related to
WPCBs in this paper, have been used for the development of techno-economical
assessment for the new mobile hydrometallurgical plant. Schematic outline of
HydroWEEE mobile plant is presented in Figure 4.
Fig.4. Outline of the mobile pilot plant placed in a transportable container [11]
The techno-economical assessment for hydrometallurgical processing route
presented in Figure 3, was applied on the small mobile plant schematically shown in
Figure 4. For this purpose the SuperPro Designer software was used. Conceptual outline
of hydrometallurgical treatment of WPCBs is shown in Figure 5.

Kamberović et al.- Hydrometallurgical process for extraction of metalsi... 145
Fig.5. Outline of hydrometallurgical treatment of WPCBs
With the intention to open up the possibility for an economic evaluation of
presented hydrometallurgical processing route, the techno-economical assessment is
achieved through the development of gold amount variation models, present in waste
material, as a crucial economical component of WPCBs. The models, developed by
SuperPro Designer software, calculate system efficiencies, total capital costs and
production (operating) costs. This methodology was applied to the development of all

146 Metalurgija-MJoM Vol 17 (3) 2011 p. 139-149
models and obtained results are directly comparable regarding time needed for return of
investment.
Assessment was performed by modeling two different amounts of input waste
material, 50kg and 100kg of WEEE per batch, following the presented solid:liquid ratio,
whereas for gold this ratio was in the range from 200ppm to 1000ppm. These data were
combined to give cost and performance analysis for the integrated system.
Prior to hydrometallurgical treatment, the mechanical pre-treatment of WPCBs
was performed. This procedure, in addition to other mechanical operations, includes
granulation of input waste material according to previously described results [1].
Therefore, presented models exclude mechanical pre-treatment cost.
Fixed parameters, i.e. total capital cost and operating cost, were calculated
according to prices in Serbia, October 2010, involving all economic factors in final
executive summary, regarding total plant direct cost, total plant indirect cost, labor,
utilities and raw material costs.
Table 4 shows results obtained by performing simulation focused on calculation
of payback time related to different amounts of gold. This calculation was used to assess
the operational time, needed to achieve economical sustainability of such
hydrometallurgical plant. Calculations were focused on the determination of total
revenues of presented hydrometallurgical process regarding gold recovery. Total
income for each model was calculated according to LME prices, October 2010 [12] for
revenues, and it was crucial to determine economic sustainability of the whole process.
Finally, based on these results, Diagrams 1 and 2 show the dependence between the
operational time needed for return on investment and gold amount present in the waste
material, concerning increase of payback time with decreasing gold amount.
Table 4. a) Calculated dependence of gold amount vs. payback time, 50 kg of waste
input material per batch
EXECUTIVE SUMMARY – 50 kg
Total Capital Investment 148,000$
Capital Investment Charged to this Project 148,000$
Operating Cost 97,000$/yr
Gold amount, Total revenues, Return on investment, Payback time,
ppm
$/yr
%
years
200 62,000 -15.97 not feasible
300 83,000 -1.96 not feasible
440 92,000 3.14 31.84
500 100,000 8.39 11.92
600 115,000 14.65 6.83
700 132,000 21.29 4.70
800 148,000 27.99 3.57
890 159,000 32.36 3.09
1000 161,000 32.95 3.02

Kamberović et al.- Hydrometallurgical process for extraction of metalsi... 147
Table 4. b) Calculated dependence of gold amount vs. payback time, 100 kg of waste
input material per batch
EXECUTIVE SUMMARY – 100 kg
Total Capital Investment 149,000$
Capital Investment Charged to this Project 149,000$
Operating Cost 144,000$/yr
Gold amount, Total revenues, Return on investment, Payback time,
ppm
$/yr
%
years
200 99,000 -21.68 not feasible
300 129,000 -2.71 not feasible
440 169,000 17.32 5.77
500 188,000 24.88 4.02
600 219,000 37.44 2.67
700 252,000 50.75 1.97
800 281,000 62.30 1.61
890 299,000 69.65 1.44
1000 339,000 85.55 1.17
Gold (ppm)
1000
900
800
700
600
500
2 4 6 8 10 12
Return on investment (year)
Diagram 1. Dependence of gold amount vs. payback time, 50 kg of waste input material
per batch

148 Metalurgija-MJoM Vol 17 (3) 2011 p. 139-149
Gold (ppm)
1000
900
800
700
600
500
400
0 1 2 3 4 5 6
Return on investment (year)
Diagram 2. Dependence of gold amount vs. payback time, 100 kg of waste input
material per batch
Conclusion
In the presented work the techno-economical feasibility of the hydrometallurgical
treatment of WPCBs has been demonstrated, concerning great environmental and
economical potentials that the development of an efficient hydrometallurgical route for
recovery of base and precious metals may offer. According to these facts the
development of such a technology responding to contemporary strict environmental
requirements would be much easier. In addition, presented hydrometallurgical
technology will allow the production of material with purity suitable for commercial
use.
According to models evaluated in this paper it is clear that the most important
economic criteria is related to gold amount present in the waste material. Following
these results, process is techno-economically feasible for amount of gold exceeding the
limit value of 500ppm. Gold and silver obtained as cement powder could be sold to
refinery or internally refined up to commercial purity Au and Ag metal powders in
small a rafination equipment.
Relatively insufficient widespread presence of hydrometallurgy in a field of
WEEE recycling still signifies domination of the pyrometallurgy. On the contrary to
SMEs requirements, it is quite clear that presented technology imply a future alternative
to pyrometalurgical process that can be readily applied in small plants, unlike large
multisector companies not so dependent on investment as well for market share.

Kamberović et al.- Hydrometallurgical process for extraction of metalsi... 149
Acknowledgments
This work has been carried out with financial support of the EU within the
project “Innovative Hydrometallurgical Processes to recover Metals from WEEE
including lamp and batteries – HydroWEEE”, FP 7 – Funding Scheme: research
activities addressed to SMEs and Ministry of Science and Technical Development,
Republic of Serbia, project “Innovative synergy of by-products, waste minimization and
clean technology in metallurgy”, No. 34033.
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