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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.
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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 eco-
friendly 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/m3.
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,
wt.%
ρ, kg/m3 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)
b)
c)
d)
e)
f)
Figure1. PCB fractions before and after dissolving in HNO3 a&b) 1.8mm; c&d)
1.0mm; e&f) 0.1mm
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
Electronic Scrap
(General composition:
Cu, Al, Fe, Sn, Pb, Zn, Ni, Ag, Au, Pd + non metallic
Shredding
Magnetic & Eddy
Current separation
Iron/steel fraction
aluminum fraction
Residue: about 90 wt.% of the total
(Cu, Sn, Pb, Zn, Ni, Ag, Au, Pd + non metallic
Solder leach
(HBF4)Solder recovery:
electrowinning
solution
solder: 7 wt.% of the total
Sn: 4.2 wt.%
Pb: 2.8 wt.%
Non metalic
Residue: about18 % of the total
(Cu, Zn, Ni, Ag, Au, Pd)
Copper leach
[Cu(II)/NH3/NH4+]
24h, 25 Csolution Copper recovery:
electrowinning
16% of the total
Residue: about 2 wt.% of the total
(Zn, Ni, Ag, Au, Pd)
Recovery of precious
metals
Separation of nickel and
zinc
Leaching
Electrowinning
Solvent
Extraction
PCB: ground
Solution:Cu(II)/NH3/NH4+
Duration: 24h, 25°C
Figure 3. The recycling process of metals contained in PCB waste
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/carroll-
text.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, Vth 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, 553562
[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
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... The three main processes are hydrometallurgical, pyrometallurgical, and a combination of both. Kamberović et al. (2018), Souada et al. (2018), and Yao et al. (2018) reported the performance of hydrometallurgical process. Their research is related to the acid leaching and the separation of metals with precipitation, solvent extraction, or electro winning. ...
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Fast industrialization has increased the demand for heavy metals, on the other hand, high-grade ore natural reserves are belittling. Therefore, alternative sources of heavy metals need to be investigated. Massive amounts of industrial wastes are being generated annually. The majority is sent to landfills or to incinerators, which eventually poses environmental challenges such as ecological contamination and health hazards to living beings. Such industrial wastes contain hazardous elements of various metals (Au, Ag, Ni, Mo, Co, Cu, Zn, and Cr), whose improper disposal leads to adverse effects to human being and the environment. As a result, methods for industrial waste management such as reuse, remanufacturing, and recycling have received much attention due to the fact that they improve cost effectiveness over time and enable the metal recovery businesses to thrive profitably. The present study provides a state of art review on the current technologies existing for the recovery of precious metals from industrial wastes streams to analyse the sustainability. Among the wastes, spent petroleum catalysts, medical waste, electronic scraps, battery wastes, metal finishing industry waste, and fly ash are some of the largest industrially-generated wastes. Various metal recovery processes involve physical, chemical, and thermal characteristics of waste streams and target metals for separation and extraction. The current challenges of pyrometallurgy, modification on the hydrometallurgy, physical and chemical methods and other advanced technologies are presented in this review. The hydrometallurgical method, which involves dissolving and leaching, is a proven and successful process for recovering metals from various raw materials. Several other recovery methods have been proposed and are currently being implemented; the problem is that most of them are only successful in retrieving certain metals based on specific properties of industrial waste. The recovered metal solutions are further concentrated and purified using adsorption, cementation, chemical precipitation, ion exchange, membrane filtration and ion flotation techniques, which can also be applied to other liquid waste streams. The recovery method only makes sense if the recovery cost is much less than the value of the precious metal. The limitations placed on waste disposal and stringent environmental legislation require environmentally-friendly metal recovery technologies. This review paper provides critical information that enables researchers to identify a proper method for metal recovery from different industrial wastes, and also it benefits researchers and stakeholders in determining research directions and making waste management-related decisions.
... The table-1 shows the pros and cons of the methods. ICMIEE20-152-3 Table 1 Pros and cons of different methods [14][15][16][17][18][19][20][21]. ...
Conference Paper
Around the world, 50 million tons of electronic waste (e-waste) is produced per year, with a 500% increasing rate in the years to come. Asia has a vast growing global economy and the total amount of e-waste is expected to rise to about 57.4 million tons by 2021. And that is more than 40% of the globally generated waste. Regarding environmental impact and increasing demand for raw materials and a gradual reduction in non-renewable sources, recycling can be a better secondary source of metals. In this paper, a survey is performed on all the existing processes of metal extraction from electronic-waste in Asia. The traditional metal separation techniques, pyrometallurgy, hydrometallurgy, electro-metallurgy, bioleaching, and mechanical processing are critically compared in this article. The introduction and future possibilities of several methods such as bio-hydrometallurgy, pyro-hydro hybrid metallurgical process, mechano-chemical technology, electro-chemical extraction are discussed. A comparison between different procedures leads to a decision on suggesting an efficient method applicable to Bangladesh. From the context of the recycling of e-waste in Bangladesh, an efficient e-waste management route is identified with defining the suitable metal extraction process.
... In leaching, solvents such as acids or caustic leaches are used to extract a soluble portion of the waste. Some commonly used leaching agents include cyanide, halide, thiourea, and thiosulfate-acids considered the most effective of all because they can leach both base and precious metals [104,107,108]. Some selected leaching agents and metals include nitric acid for base metals, sulfuric acid, or aqua regia for copper, thiourea or cyanide for gold and silver, and hydrochloric acid or sodium chlorate for palladium [109]. ...
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Chapter
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The behavior of impurity elements during a copper recovery process from waste printed circuit board (PCB) using ammonia–ammonium sulfate and chloride systems are examined and the performance of these two systems are compared. Leaching of PCB was carried out by solutions containing copper(II) ammine complexes as the oxidizing agent. The copper was selectively dissolved but the leach solution also contained zinc (∼ 1 g/L), lead and manganese (∼ 0.1 g/L), in addition to 40–50 g/L copper.The solution was then purified by solvent extraction using LIX 26 (alkyl substituted 8-hydroxy-quinoline) which typically extracted > 95% of the impurity elements with a few exceptions. The selectivity in the leaching and purification steps was higher in the sulfate system than that in the chloride system. Finally, copper was recovered from the solution by electro-deposition with a low power consumption of 1300 and 500 kWh/tonne in the sulfate and chloride systems, respectively.The results of glow discharge mass spectrometry of the electro-deposited copper revealed that the electro-deposited copper contained 24 and 1.1 ppm of impurities in the sulfate and chloride systems, respectively, with lead as the main impurity element in both systems. Because the purity of the copper deposit from the chloride system was high, this copper scrap recycling process has the potential to recover high purity copper from wastes with a low power consumption.
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In Korea due to rapid economical growth followed by urbanisation, breakage of large traditional families into small nuclear families, continuous changes in equipment features and capabilities causes tremendous increase in sale of new electrical and electronic equipment (EEE) and decrease in sale of used EEE. Subsequently, the ever-increasing quantity of waste electrical and electronic equipment (WEEE) has become a serious social problem and threat to the environment. Therefore, the gradual increase in the generation of WEEE intensifies the interest for recycling to conserve the resources and protect the environment. In view of the above, a review has been made related to the present status of the recycling of waste electrical and electronic equipment in Korea. This paper describes the present status of generation and recycling of waste electrical and electronic equipment, namely TVs, refrigerators, washing machines, air conditioners, personal computers and mobile phones in Korea. The commercial processes and the status of developing new technologies for the recycling of metallic values from waste printed circuit boards (PCBs) is also described briefly. Since 1998, three recycling centers are in full operation to recycle WEEE such as refrigerators, washing machines and air conditioners, having the total capacity of 880,000 units/year. All waste TVs are recently recycled on commission basis by several private recycling plants. The recycling of waste personal computers and mobile phones is insignificant in comparison with the amount of estimated obsolete those. Korea has adopted and enforced the extended producer responsibility (EPR) system. Korea is making consistent efforts to improve the recycling rate to the standards indicated in the EU directives for WEEE. Especially environmentally friendly and energy-saving technologies are being developed to recycle metal values from PCBs of WEEE.
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The paper summarizes the present and future course of biosorption and bioaccumulation, as the branch of science, pointing out on their basic assumptions, philosophy and the goals. The processes are presented as new tools for separation technologies of XXI century. The paper is the discussion with the literature on the future prospects of those processes, pointing out that research should be oriented on the practical applications, in order to make technologies from the processes and also discusses other than environmental possible future applications. It presents an own point of view on these techniques, after some years of working in this very area. Biosorption and bioaccumulation, involve interactions and concentration of toxic metals or organic pollutants (e.g. dyes) in the biomass, either living (bioaccumulation) or non-living (biosorption). The processes play an important role in natural cycling of matter in the environment. The paper discusses the possibilities which offer research on pollutants-biomass interactions, pointing out that the key to elaborate an efficient method working for the nature would be to understand the mechanisms governing the processes, parameters which influence both equilibrium and kinetics, through the observation of naturally occurring phenomena. Only then we would be able to control and carry out under industrial regime, so the processes would work beneficially for the environment.
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Waste printed circuit boards (WPCB) have an inherent value because of the precious metal content. For an effective recycling of WPCB, it is essential to recover the precious metals. This paper reports a promising method to recover the precious metals. Aqua regia was used as a leachant and the ratio between metals and leachant was fixed at 1/20 (g/ml). Silver is relatively stable so the amount of about 98 wt.% of the input was recovered without an additional treatment. Palladium formed a red precipitate during dissolution, which were consisted of Pd(NH(4))(2)Cl(6). The amount precipitated was 93 wt.% of the input palladium. A liquid-liquid extraction with toluene was used to extract gold selectively. Also, dodecanethiol and sodium borohydride solution were added to make gold nanoparticles. Gold of about 97 wt.% of the input was recovered as nanoparticles which was identified with a high-resolution transmission electron microscopy through selected area electron diffraction and nearest-neighbor lattice spacing.
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The constant growth in generation of solid wastes stimulates studies of recycling processes. The electronic scrap is part of this universe of obsolete and/or defective materials that need to be disposed of more appropriately, or then recycled. In this work, printed circuit boards, that are part of electronic scrap and are found in almost all electro-electronic equipments, were studied. Printed circuit boards were collected in obsolete or defective personal computers that are the largest source of this kind of waste. Printed circuit boards are composed of different materials such as polymers, ceramics and metals, which makes the process more difficult. However, the presence of metals, such as copper and precious metals encourage recycling studies. Also the presence of heavy metals, as Pb and Cd turns this scrap into dangerous residues. This demonstrates the need to search for solutions of this kind of residue, in order to have it disposed in a proper way, without harming the environment. At the first stage of this work, mechanical processing was used, as comminution followed by size, magnetic and electrostatic separation. By this process it was possible to obtain a concentrated fraction in metals (mainly Cu, Pb and Sn) and another fraction containing polymers and ceramics. The copper content reached more than 50% in mass in most of the conductive fractions and significant content of Pb and Sn. At the second stage, the fraction concentrated in metals was dissolved with acids and treated in an electrochemical process in order to recover the metals separately, especially copper. The results demonstrate the technical viability of recovering copper using mechanical processing followed by an electrometallurgical technique. The copper content in solution decayed quickly in all the experiments and the copper obtained by electrowinning is above 98% in most of the tests.
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Computer circuit board scrap was first treated with one part concentrated nitric acid and two parts water at 70 degrees C for 1 h. This step dissolved the base metals, thereby liberating the chips from the boards. After solid-liquid separation, the chips, intermixed with some metallic flakes and tin oxide precipitate, were mechanically crushed to liberate the base and precious metals contained within the protective plastic or ceramic chip cases. The base metals in this crushed product were dissolved by leaching again with the same type of nitric acid-water solution. The remaining solid constituents, crushed chips and resin, plus solid particles of gold, were leached with aqua regia at various times and temperatures. Gold was precipitated from the leachate with ferrous sulphate.