Gold From Scrap

8/10/2019 Gold From Scrap

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Introduction

Fast electronic industry development brought the great benefits in everyday life,but its consequences are usually ignored or even unknown. Used electronic equipmentbecame one of the fastest growing waste streams in the world. From 20 to 50 milliontonnes of waste electical and electronic equipment (WEEE, e-waste) are generated eachyear, bringing significant risks to human health and the environment [1]. EU legislativerestricts the use of hazardous substances in electrical and electronic equipment (EEE)(Directive 2002/95/EC) such as: lead, mercury, cadmium, chromium and flameretardants: polybrominated biphenyls (PBB) or polybrominated diphenyl ethers (PBDE)and also promotes the collection and recycling of such equipment (Directive2002/96/EC). They have been in implementation since February 2003. Despite rules oncollection and recycling only one third of electrical and electronic waste in theEuropean Union is reported as appropriately treated and the other two thirds are sent tolandfills and potentially to sub-standard treatment sites in or outside the EuropeanUnion. In December 2008 the European Commission proposed to revise the directiveson 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, inpast two decades have been based on recovery via material smelting. This is highlypolluting, primitive recycling technology that can cause a variety of environmentalproblems. It is mostly processed, sometimes illegally, in developing countries, forinstance China, India, Pakistan and some African countries [3,4]. Goosey and Kellner intheir 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 bymechanical processing, pyrometallurgy, hydrometallurgy, biohydrometallurgy or acombination of these techniques.

Pyrometallurgy, as traditional method to recover precious and non-ferrous metalsfrom e-waste, includes different treatments on high temperatures: incineration, meltingetc. Pyrometallurgical processes could not be considered as best available recyclingtechniques anymore because some of the PCB componenets, especially plastics andflame retardants, produce toxic and carcinogenic compounds. The most of the researchactivities on recovery of base and precious metals from waste PCBs are focused onhydrometallurgical techniques for they are more exact, predictable and easily controlled[6,7].

In recent years the great number of investigations have been conducted in orderto solve the problem of WEEE and develop appropriate recycling techniques. Accordingto Cui and Zhang [7] recycling of e-waste can be broadly divided into three major steps:a) disassembly-mechanical pretreatment: selectively removing hazardous and valublecomponents for special treatment and it is necessary step for further operations, b)concentrating: increasing the concentration of desirable materials using mechanicaland/or metallurgical processing and c) refining: metallurgical treatment and purificationof desirable materials.

Hydrometallurgu, i.e. leaching and cementation process in Serbian mine Bor wasfirst mentioned in 1907 when 200 tons of copper were produced. Since those days tilltoday copper hydrometallurgy has not mount at Serbia and nearby region [8].

Hydrometallurgical processing consist of: leaching transfering desirablecomponents into solution using acides or halides as leaching agents, purification of the


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Kamberoviet 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, dueto their ability to leach both base and precious metals. Generally, base metals areleached in nitric acid [9, 10]. The most efficient agent used for solder leach isfluoroboric acid [11]. Copper is leached by sulphuric acid or aqua regia [12]. Aqua regiais also used for gold and silver [11], but these metals are usually leached by thiourea orcyanide [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 sorbheavy metals from aqueous solutions [14]. This is physico-chemical mechanism basedon ion-exchange [15], metal ion surface complexation adsorption or both [16].

Oishi et al. [17] conducted research on recovery of copper from PCBs byhydrometallurgical techniques. Proposed process consists of leaching, solvent extractionand electrowinning. In the first stage of research conducted by Veit et al. [12]mechanical processing was used as comminution followed by size, magnetic andelectrostatic separation. After pretreatment, the fraction with concentrated Cu, Pb andSn was dissolved with acids and treated in an electrochemical process in order torecover the metals separately, especially copper, with two different solutions: aqua regiaand 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 significantachievement of this research was synthesis of pure gold nanoparticles.

Sheng and Etsell [9] investigated leaching of gold from computer chips. The firststage was leaching of base metals with nitric acid and the second, leaching of gold withaqua regia due to its flexibility, ease and low capital requirement. Non-metallicmaterials are also recovered this way, mainly plastic and ceramics. Quinet et al. [18]carried out bench-scale extraction study on the applicability of economically feasiblehydrometallurgical processing routes to recover silver, gold and palladium from wastemobile phones. Selective extraction of dissolved metals from solution is very difficultand 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 PCBswith obtained by mechanical pretreatment of waste computers.

The mechanical pretreatment of end-of-life computers was performed atSETrade, Belgrade. The first stage was manual disassembling of computers, liberationof PCBs and removal of the batteries and capacitors. Liberated PCBs were milled inQZ-decomposer, separating magnetic materials from non magnetic fractions, whilealuminum was manually removed from conveyor belt. Material was then milled inshredder Meccano Plastica, after which material was not exposed to another magneticseparation.

Characterization of granulated waste PCBs included determination of followingparameters: pouring density, percentage of magnetic fraction, particle size distribution,


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234 MJoM Vol 15 (4) 2009 p.231-243

rate of metal components leachability using optical microscopy, atomic absorptionspectrometry (AAS), X-ray fluorescent spectrometry (XRF) and volumetric analysis.Also, appropriate hydrometallurgical system for evaluation of metal components andoptimization of process parameters: temperature, time, solid:liquid ratio and mixingvelocity are selected.

Sieve analysis was performed using Taylor type sieves and mass of fractionsobtained after 30 minutes sieving was measured. Percentage of each fraction wascalculateded.

The pouring density of total sample and of each fraction was measured usingHall flowmeter funnel (ASTM B13). Pouring density of total sample was 889 kg/m3.

The sample was subjected to the magnetic separation process using twopermanent 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 boilingtemperature with agitation followed by filtration after cooling. Metallic fraction istransferred 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.%

, kg/m3 Metallic part,wt.%

5.000 7.07 800 43.842.500 37.24 880 50.44

2.000 6.99 830.15 55.471.800 8.50 986.33 38.861.250 11.68 1235.63 31.571.000 5.61 1474.61 48.480.800 5.42 1136.59 61.250.630 4.81 1022.48 43.950.500 1.64 958.63 50.200.400 2.75 908.81 44.260.315 2.47 794.15 41.310.250 1.16 656.74 37.870.100 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 infraction +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 dissolvingin nitric acid and removal of metallic components.


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Analysis of chemical composition of granulated PCBs was performed usingvolumetric analysis, AAS and XRF spectrometry. Materials used for presented analysiswere both granulated samples and samples after sieve analysis dissolved in 50 vol.%HNO3.

Volumetric analysis was performed using standard sodium tiosulphate solutionfor treatment of samples dissolved in 50 vol.% HNO3. Results showed that coppercontent in granulated PCBs was 21.61 wt%. Also, distribution of copper in fractionswas determined by volumetric analysis as presented in Table 2.

Table 2. Distribution of copper in fractions

fraction, mm Cu, wt.%

5.000 21.962.500 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 performedby Perkin Elmer 4000 spectometer calibrated with standard solutions for each measuredmetal. Results of experimental analysis are shown in Table 3.


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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 3.560.500 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 wasnot 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 analysiswas 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


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Table 4. Results of XRF analysis

Cu Ag Rh Pd Pt Au

Lom 1 96.254 3.746Lom 2 95.072 4.928Lom 3 73.121 6.45 2.521 17.943Lom 3 30.749 14.762 8.806 2.353 43.33Lom 4 95.03 4.97

XRF analysis showed that metal content varies from sample to sample and ithighly depends on measuring spot.

Based on detailed literature review and presented experimental results, severalprocess option were selected as an appropriate hydrometallurgical process for extractionof metals from electronic waste was.

Process option 1-The use of selective leachants and recovery of high purity

metals from PCBsThis 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 andelectrowinning [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.


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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 totalSn: 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 totalResidue: about 2 wt.% of the total

(Zn, Ni, Ag, Au, Pd)

Recovery of precious

metals

Separation of nickel and

zinc

Leaching

Electrowinning

SolventExtraction

PCB: groundSolution:Cu(II)/NH3/NH4

+

Duration: 24h, 25C

Figure 3. The recycling process of metals contained in PCB waste

Process option 2- The use of conventional leachants for recovery of metals fromwaste PCBs

This process option represents bench-scale method for extraction and recovery ofcopper and precious metals from waste PCBs. After comminution, material wassubjected to serial of hydrometallurgical processing routes: sulphuric acid leaching and

precipitation for Cu recovery; chloride leaching followed by cementation for Pd, Ag, Auand Cu recovery and cyanidation and activated carbon adsorption for recovery of Auand Ag. The proposed flowsheet is presented in Figure 4.


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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

PCBsThis process option is particulary based on recovery of gold from electronic

waste using an eco-friendly or green reagents. After communition, non-toxicreagents formic acid and potassium persulphate are used for Au leaching at boilingtemperature. 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.


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Fig. 5. Flow sheet of gold recovery from gold-plated PCBs (GPCB), gold-coated glassbangles (GCGB) and gold-coated mirrors (GCM)


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242 MJoM Vol 15 (4) 2009 p.231-243

Conclusion

On the basis of experimental results it can be concluded that properties ofinvestigated material is in accordance with literature and it could be a representative forselection of proper hydrometallurgical recycling technique. AAS chemical analysis hasshown that fraction above 5 mm contained high amount of Fe and should be avoided bymore efficient magnetic separation. Also, -0.1 mm fracton can cause various difficultiesin process, great loses due to large content of metals in this fraction and decreasedleachability.

Final selection of the process which could be applied for further analysisdepends on input materials characteristics. There is no completely green option.Selection of suitable hydrometallurgical process highly depend on leaching tests andtechno-economical analysis and possible solution for electronic waste lies incombination 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 wasteelectrical and electronic equipment in Korea, Resources, Conservation andRecycling 50 (4), 2007, 380397

[7] J. Cui, L. Zhang, Metallurgical recovery of metals from electronic waste: Areview, Journal of Hazardous Materials, 158 (2-3), 2008, 228256

[8] . Kamberovi, D. Sinadinovi, M. Soki, M. Kora, Hydrometallurgicaltreatment of refractory and polymetallic copper ores, Vth Congress of theMetallurgists 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 scrapusing aqua regia, Waste Management and Research, 25 (4), 2007, 380383[10] R. Vraar, Vukovi N., Kamberovi ., 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 circuitboards, Journal of Hazardous Materials 164 (2-3), 2009, 1152 1158

[12] H. M. Veit, A. M. Bernardes, J. Z. Ferreira, J. A. Soares Tenrio, C. de FragaMalfatti, Recovery of copper from printed circuit boards scraps by mechanical


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processing and electrometallurgy, Journal of Hazardous Materials, 137 (3), 2006,17041709

[13] . Kamberovi, D. Sinadinovi, M. Kora, Metallurgy of gold and silver (inSerbian), SIMS, 2007

[14] K. Chojnacka, Biosorption and bioaccumulation the prospects for practicalapplications, 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, SouthAfrica, 2005, 553562

[16] B.C. Qi, C. Aldrich, Biosorption of heavy metals from aqueous solutions withtobacco dust, Bioresource Technology, 99 (13), 2008, 55955601

[17] T. Oishi, K. Koyama, S. Alam, M. Tanaka, J. C. Lee, Recovery of high puritycopper cathode from printed circuit boards using ammoniacal sulphate orchloride solutions, Hydrometallurgy 89 (1-2), 2007, 8288

[18] P. Quinet, J. Proost, A. Van Lierde, Recovery of precious metals from electronicscrap by hydrometallurgical processing routes, Minerals and MetallurgicalProcessing, 22 (1), 2005, 1722

[19] J. Pavlovi, S.Stopi, B.Friedrich, . Kamberovi, Selective Removal of HeavyMetals 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, tinalloys or lead alloys from printed circuit boards


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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)

eljko Kamberovi1*, Marija Kora2, Milisav Ranitovi2

1Faculty of Technology and Metallurgy, University of Belgrade, Serbia

2Innovation center of the Faculty of Technology and Metallurgy, Belgrade,Serbia

Received 13.06.2011

Accepted 15.08.2011

AbstractRapid technological development induces increase of generation of used electric

and electronic equipment waste, causing a serious threat to the environment. Wasteprinted circuit boards (WPCBs), as the main component of the waste, are significantsource of base and precious metals, especially copper and gold. In recent years, most ofthe activities on the recovery of base and precious metals from waste PCBs are focusedon hydrometallurgical techniques as more exact, predictable and easily controlledcompared to conventional pyrometallurgical processes. In this research essential aspectsof the hydrometallurgical processing of waste of electronic and electrical equipment(WEEE) using sulfuric acid and thiourea leaching are presented. Based on thedeveloped flow-sheet, both economic feasibility and return on investment for obtained

processing conditions were analyzed. Furthermore, according to this analysis, SuperProDesigner software was used to develop a preliminary techno-economical assessment of

presented hydrometallurgical process, suggested for application in small mobile plantaddressed to small and medium sized enterprises (SMEs). Following of this paper, thedescribedprocess is techno-economically feasible for amount of gold exceeding thelimit 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: eljko Kamberovi, [email protected]


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140 Metalurgija-MJoM Vol 17 (3) 2011 p. 139-149

IntroductionAs a result of rapid technical and technological development, waste electric and

electronic equipment (WEEE) is becoming one of the major environmental risks for itshigh quantity and toxicity in recent years. In terms of materials and components WEEEis non-homogeneous and very complex, and the major challenge for recyclingoperations is how to respond to poor recovery of metals by mechanical treatment as wellto 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 complexcomposition, 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 andprecious metals [1, 2, 3]. The state of the art in recovery of precious metals fromelectronic waste highlights two major recycling techniques, such as pyrometallurgicaland 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 hasbeen 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 forrecovery of metals from electronic waste [7, 8].

This paper describes essential aspects of the hydrometallurgical processing ofWEEE using sulfuric acid and thiourea leaching. Previous studies, reported by authors[9, 10] were conducted in order to investigate optimal processing conditions concerninghydrometallurgical recovery of base and precious metals from WPCBs. In this papersome results obtained in these studies are also presented. Based on these results,regarding characterization and development of the hydrometallurgical treatment ofwaste material, both economic feasibility and return on investment for obtained

processing conditions were analyzed. Furthermore, this analysis was used in order todevelop a preliminary techno-economical assessment of presented hydrometallurgical

process adopted for use in small mobile plant taking into account limitation of necessaryquantities of waste material as well as investment, addressed to small and medium sizedenterprises (SMEs).

MaterialsMaterial used in presented research is comminuted and mechanically pre-treated

waste PCBs, as described in previous studies by authors [1, 9, 10]. Chemicalcomposition of two samples was analyzed using atomic absorption spectroscopy, X-rayfluorescence spectroscopy and, inductively coupled plasma atomic emissionspectroscopy. Obtained results together with literature data are presented in Table 1. Inthis paper, fractions (F), 0.071mm< F


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Kamberoviet al.- Hydrometallurgical process for extraction of metalsi... 141

2mm and -1mm was examined in therange of 100 to 700 rpm. Solution used for testingwas 30 wt. % NaCl, whose density matches the density of H2SO4 solution used forleaching.

Table 1. Chemical composition of sample of WPCBs [9]

Materials Sample 1*%(w/w)

Sample 2**%(w/w)

Literature data [3]%(w/w)

Cu 27.99 25.24 20Al 0.47 0.69 2Pb 2.17 2.22 2Zn 2.01 2.05 1

Ni 1.23 0.93 2Fe 1.18 0.98 8Sn 3.26 3.17 4

Au/ppm 440 890 1000Pt/ppm 57 17 -Ag/ppm 1490 1907 2000Pd/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 thestirring 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 thecontainer are raised and caught mixing while floating particles slowly transit into thesolution. Finally, at 600 rpm all particles of the waste materials are fully affected bymixing.

In the industrial leaching conditions, stirring rate of 600 rpm is relatively highand could cause great trouble for carrying out of the process of leaching. It is assumedthat with proper solid:liquid ratio, results obtained at 300 rpm will be satisfactory, and

thusthis 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, steelimpeller, oxygen dispersion tube and hydrogen peroxide dozer. Experimental set up isshown in Figure 1.

Electrowinning (EW) was performed in a rectangular electrolytic cell withdimensions 10088300mm with effective volume 2000 mL made of high density

polypropylene. The cathode material was copper (Cu 99,99%) and anode was leadantimony alloy (PbSb7).


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Fig.1. Experimental apparatus for leaching: 1.Electro-resistant heater; 2.Reactionglass vessel; 3.Cooler with condenser; 4.Mixer; 5.Oxygen tube; 6.Peroxide dozer;

7.Digital pH and temperature measurement device

Results and discussionOptimum processing conditions were obtained by variation of different leaching

parameters. Hydrometallurgical extraction of copper from the waste material wasperformed using sulfuric acid as leaching agent. Solid residue after copper leachingstep, was leached by thiourea in the presence of ferric ion (Fe2(SO4)3) as an oxidant insulfuric acid solution, in order to extract gold. In the case of copper leaching, analysiswas performed for both, laboratory and pilot scale, while gold leaching was tested onlyfor laboratory scale. According to summarized results, optimum copper and goldleaching parameters are presented in Table 2.

Table 2. Optimal gold and copper leaching conditions

Copper leachingParameterLaboratory scale Pilot scale

Gold leaching

Acid conc.H2SO4conc. 1.5-2M 1.5-2M 10 g dm

-3thiourea conc. / / 20 g dm-3Oxidants conc.

H2O2 40mL/h 50 kg/t /O2 16L/h 80 L/kg/h /

Fe3+ / / 6 g dm-3Solid-liquid ratio 50-100g/L 150-200g/L 20 % of solid

Temperature 75-80C 70C 40CStirring rate >300rpm ~300rpm 600 rpm

Time >5h


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EW was performed in order to extract metallic copper from leaching solution.Optimal EW conditions are shown in Table 3, while obtained copper deposit isillustrated in Figure 2.

Table 3. Optimal EW conditions

Voltage 2.1V

Currentdensity

120-200A/m2

Temperature 40C

Time 15h

Steering rate 100rpm

Fig.2. Copper deposited on the cathode

According to presented optimal processing parameters, block diagram forhydrometallurgical recovery of base and precious metals, using selective leachingagents from WPCBs was developed. Block diagram for hydrometallurgical processingof 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]


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Although hydrometallurgy is relatively widely used in base and precious metalsprocessing plants, the objective of this work was to discuss the possibility of providing apurely 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 entirelyhydrometallurgical route for use in small mobile plant, economic benefits for SMEsmay be possible, regarding low capital investment and necessary quantities of wastematerial.

Process option investigated in this paper was based on preliminary results carriedout on the pilot scale in the scope of the European project InnovativeHydrometallurgical 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 processfor recovery of base and precious metals from fluorescent powders coming from CRTand spent lamps, printed circuit boards, LCD and lithium spent batteries. Theexperience and knowledge obtained in the preliminary pilot plant tests gave importanttechnological indications for the development of the small mobile plant HydroWEEE.Furthermore results obtained during the activities of project, particularly related toWPCBs in this paper, have been used for the development of techno-economicalassessment for the new mobile hydrometallurgical plant. Schematic outline ofHydroWEEE 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 routepresented in Figure 3, was applied on the small mobile plant schematically shown inFigure 4. For this purpose the SuperPro Designer software was used. Conceptual outlineof hydrometallurgical treatment of WPCBs is shown in Figure 5.


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models and obtained results are directly comparable regarding time needed for return ofinvestment.

Assessment was performed by modeling two different amounts of input wastematerial, 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 werecombined to give cost and performance analysis for the integrated system.

Prior to hydrometallurgical treatment, the mechanical pre-treatment of WPCBswas performed. This procedure, in addition to other mechanical operations, includesgranulation 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 calculatedaccording 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 calculationof payback time related to different amounts of gold. This calculation was used to assessthe operational time, needed to achieve economical sustainability of suchhydrometallurgical plant. Calculations were focused on the determination of totalrevenues of presented hydrometallurgical process regarding gold recovery. Totalincome for each model was calculated according to LME prices, October 2010 [12] forrevenues, 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 theoperational time needed for return on investment and gold amount present in the wastematerial, concerning increase of payback time with decreasing gold amount.

Table 4. a) Calculated dependence of gold amount vs. payback time, 50 kg of wasteinput material per batch

EXECUTIVE SUMMARY 50 kgTotal Capital Investment 148,000$

Capital Investment Charged to this Project 148,000$Operating Cost 97,000$/yr

Gold amount,

ppm

Total revenues,

$/yr

Return on investment,

%

Payback time,

years

200 62,000 -15.97 not feasible300 83,000 -1.96 not feasible440 92,000 3.14 31.84500 100,000 8.39 11.92

600 115,000 14.65 6.83700 132,000 21.29 4.70800 148,000 27.99 3.57890 159,000 32.36 3.091000 161,000 32.95 3.02


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Table 4. b) Calculated dependence of gold amount vs. payback time, 100 kg of waste

input material per batch

EXECUTIVE SUMMARY 100 kgTotal Capital Investment 149,000$

Capital Investment Charged to this Project 149,000$Operating Cost 144,000$/yr

Gold amount,ppm

Total revenues,$/yr

Return on investment,%

Payback time,years

200 99,000 -21.68 not feasible300 129,000 -2.71 not feasible440 169,000 17.32 5.77

500 188,000 24.88 4.02600 219,000 37.44 2.67700 252,000 50.75 1.97800 281,000 62.30 1.61890 299,000 69.65 1.441000 339,000 85.55 1.17

2 4 6 8 10 12

500

600

700

800

900

1000

Gold(ppm)

Return on investment (year)

Diagram 1. Dependence of gold amount vs. payback time, 50 kg of waste input material

per batch


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Acknowledgments

This work has been carried out with financial support of the EU within theproject Innovative Hydrometallurgical Processes to recover Metals from WEEEincluding lamp and batteries HydroWEEE, FP 7 Funding Scheme: researchactivities addressed to SMEs and Ministry of Science and Technical Development,Republic of Serbia, project Innovative synergy of by-products, waste minimization andclean technology in metallurgy, No. 34033.

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Hydrometallurgical process for extraction of metals from electronic waste-Part I,Metalurgija Journal of Metallurgy, 15 (4), 231 244, 2009

[2] J. Cui, E. Forssberg, Mechanical recycling of waste electric and electronicequipment: a review, Journal of Hazardous Materials B99, 243-263, 2003

[3] I.O. Ogunniyi, M.K.G. Vermaak, D.R. Groot, Chemical composition andliberation characterization of printed circuit board comminution fines for

beneficiation investigations Waste Management, 29 (7), 2140-2146, 2009[4] J.E.Hoffmann, Recovering precious metalsf rom electronic scrap, Jom-J. Miner.

Met. Mater. Soc. 44 (7), 4348, 1992[5] E.Y.L.Sum, The Recovery of Metals from Electronic Scrap, Jom-J.Miner. Met.

Mater. Soc. 43 (4), 5361, 1991[6] J.-c. Lee, H.T. Song, J.-M. Yoo, Present status of the recycling of waste

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[8] P. Quinet, J. Proost, A. Van Lierde, Recovery of precious metals from electronicscrap by hydrometallurgical processing routes, Miner. Metall. Process. 22 (1)(2005) 1722.

[9] . Kamberovi, M. Kora, S.Vraar, M. Ranitovi, Preliminaryprocess analysisand development of hydrometallurgical process for the recovery of copper fromwaste printed circuit boards, 8th International Symposium and EnvironmentalExhibition - Going Green CARE INNOVATION 2010, November 8-11, 2010,Vienna, Austria

[10] . Kamberovi, M. Kora, D. Ivi, V. Nikoli, M. Ranitovi, Process selectionfor hydrometallurgical WPCBs recycling, 4th International Conference Processing and Structure of Materials, Pali, Serbia, 2010., Proceedings 67-72

[11] F. Veglio, F. Beolchini, F. Pagnanelli, L. Toro, B. Kopacek, Process analysis,process design of pilot plant, first practical experiences in the pilot plant, 8thInternational Symposium and Environmental Exhibition - Going Green CAREINNOVATION 2010, November 8-11, 2010, Vienna, Austria

[12] London Metal Exchange, www.lme.com

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Gold From Scrap