Copper and lead recovery from discarded printed circuit boards by electrolysing leached solution - Tran Thi Phuong Thao

Journal of Science and Technology 55 (1B) (2017) 129–137 COPPER AND LEAD RECOVERY FROM DISCARDED PRINTED CIRCUIT BOARDS BY ELECTROLYSING LEACHED SOLUTION Tran Thi Phuong Thao1, *, Nguyen Trung Hai Thinh1, Ung Thai Le Anh1, Lam Nguyen Tuong Dao2, Tran Van Man1, 2, Nguyen Nhi Tru3 1 Department of Physical Chemistry, Faculty of Chemistry, University of Science – VNU HCM 227 Nguyen Van Cu Street, Ward 4, District 5, Ho Chi Minh City, Vietnam 2Laboratory of Applied Physical Chemistry, Faculty of Chemistry, University of Science – VNUHCM, 227 Nguyen Van Cu Street, Ho Chi Minh City, Vietnam 3Department of Energy Materials and Applications, Faculty of Materials Technology, HCMUT – VNUHCM, 268 Ly Thuong Kiet Street, District 10, Ho Chi Minh City, Vietnam *Email: closefriend83@gmail.com Received: 30 December 2016; Accepted for publication: 3 March 2017 ABSTRACT Results of copper and lead recovery from discarded printing circuit boards (PCB) by acidic dissolution and electrodeposition are presented. A preliminary procedure of the recovery process is proposed with the following steps: disposal of the mounted electrical elements, cleaning, grinding, iron separation for grains screening, metal dissolution, and electrolysis. The composition analysis is performed to define suitable electrochemical parameters for recovery. XRF and AAS techniques are used for preliminary estimation of metal content in leached solution. LSV method is implemented to establish parameters for copper electrodeposition. The product quality is evaluated through XRD analysis. The high recovery efficiencies, 97.61% and 96.59 % for copper (in metallic form) and lead (in dioxide form), respectively, were reached. Keywords: printing circuit board, copper and lead recovery, dissolution, electrodeposition. 1. INTRODUCTION Due to the growing consumption of electronic devices and tendency of their shorter end– of–life, the modern world is facing a rapid accumulation of electronic wastes (e–waste). With global discarded amount estimated at 41.8 million tons in 2014 [1, 2] and 4–5 % increase annually [3], e–waste has become an emerging problem for the environment nowadays. However, alongside the negative impact on environmental issues, which are to be solved by appropriate treatment measures, e–waste is considered as a potential reusable resource for different materials, especially metals and their compounds. Yan Xu et al. data for 2014 provide a considerable quantity of iron (16.5 million tons), copper (1.9 million tons), gold (300 tons), and a significant amount of other precious metals such as silver, palladium, etc. with an estimated Copper and lead recovery from discarded printed circuit boards by electrolysing leached solution 130 value of about US $52 billion [2]. Discarded printing circuit boards (PCB), which has been recovered for years, comprise a substantial amount of valuable metals. Copper and lead are the main metals recovered due to their higher contents in discarded PCB and in e–wastes. Various processes have been applied to extract these metals and have normaly been divided on thermal and non–thermal methods including chemical and/or electrochemical steps [3]. Based on the different deposition potentials, the electrochemical approach has widely been applied to remove various metals from leachates. According to Vijayaram R. et al. [3], copper could be obtained from PCB waste by non– thermal method through chemical treatment with 8.5 – 92.7 % efficiency, depending on used acid compositions. Nitric acid and its mixture with hydrochloric acid are proven to be the most suitable solvents for copper extraction. Similarly, Andrea M. and Keith S. [4] used nitric acid to dissolve copper and lead. Metallic copper and lead in the lead dioxide form were recovered in the followed step by electrolysis. Kumar M. et al. [5] reported 98.3 % efficiency of copper recovery from leachate under optimum conditions of 800 rpm agitation and 60 oC using 3 mM/L nitric acid. Sulfuric acid was also used as leaching agent to extract copper and other metals from e–wastes [6–9]. Due to the unavailability of direct copper transformation into its sulfate salt, oxidizing agents such as hydrogen peroxide are required. With 1 M H2SO4+H2O2 mixture, 82.1 % dissolution efficiency was reached by Nguyen T. T. H. et al. [9]; meanwhile, 88.07 % extraction efficiency was shown for copper by Zhang Z. J. [2]. To improve the copper extraction, aqua regia was added to sulfuric acid and 98 % efficiency was reported by Weit H. M. et al. [6]. Nowadays, selective and efficient recovery of metals from e–waste is considered a challenging issue. In this paper, the results of copper and lead recovery from discarded PCB are provided based on a non–thermal technique using nitric acidic as leaching agent followed by electrodeposition. 2. MATERIALS AND METHODS 2.1. Procedure of PCB recycling process Discarded PCBs were collected from e–waste slump and all active and passive components were dismantled before transferring to the recycling process. The scraps were thoroughly rinsed, dried, weighed and fed to ball milling process until powder with maximal grain sizes of 1 mm was achieved. Then, a magnetic device was used to separate iron fillings from the powder. The following steps were conducted as described according to the block diagram in Figure 1. This diagram was designed based on a generally accepted procedure [3, 10] with some modifications: by adding the second electrolysis step for copper deposition and the anodic lead removal. The modifications were introduced assuming that both metals occurred at high content in PCB scraps and copper recovery was preferential as more valuable material. The grinded powder was dissolved in 6 M nitric acid (1 :1 ratio) at room temperature, followed by filtration to separate leachate from residues containing H2SnO3 and other solid substances. The leached solution was then analyzed to reveal elemental contents and underwent first step electrolysis afterwards. ele wa ele sol con com 2.2 con vo ele per pe ele con ele me PbO2 and ctrodepositi ter, dried a ctrodepositi ution using ducted for pound in f . Electroche A prelim ducted on ltammetry ( ctrode, plat formed in a The linea aks during ctrolysis. P ducted for ctrode. Sur asurements copper wer on process. nd weighed on after diss nitric acid to metallic le orm of PbO2 Fi mical inves inary electr Metrohm A CV) techniq inium count potential wi r sweep volt electrolysis, otential swe similar cell face area were conduc e deposited The formed . Simultane olution in 6 receive Pb ad depositio was recover gure 1. Block tigation ochemical i utolab PGS ue in the er electrode ndow rangin ammetry (L followed b pt at 2 mV with Ag/A of copper ted on the B on the anod anodic prod ously, the M nitric aci 2+ solution, n. Howeve ed and the l diagram of P nvestigation TAT 30 p conventiona , and Ag/A g from –0.8 SV) was als y further d /s scan rate gCl referenc working el iologic MPG e and catho uct was the cathodic co d. The obtai from which r, in this w ast step was CB treatmen of mixed otentiostat ( l three elec gCl referen to 0.5 V at 5 o applied to etermination and in the e electrode ectrode wa 2 (France). Tran Th de respectiv n separated, pper was p ned PbO2 ca the second ork the fin not conduct t process. copper and The Nether trode cell w ce electrode 0 mV/s scan identify red of optimal range of – and platiniz s defined a i Phuong Th ely as a resu rinsed with urified by n be transfe step electro al product ed. lead solu lands), usin ith glassy . The scann rate. uction and o current de 0.9 to –0. ed titanium s 0.071 c ao, et al. 131 lt of the distilled repeated rred into lysis was for lead tion was g cyclic working ing was xidation nsity for 1 V was counter m2. The Copper and lead recovery from discarded printed circuit boards by electrolysing leached solution 132 Electrodeposition was processed in an electrolyzer with GW Instek GPR–3510HD DC power supply at various current densities and solution stirring of 600 rpm. As in LSV case, copper and platinized titanium were selected as cathode and anode respectively. The efficiency of the electrolysis process was determined as a percentage ratio between the experimental data obtained by mass gain method (difference of the electrode mass weighed before and after electrolysis) and the data calculated by Faraday law (m୊ୟ୰. ൌ ୑୸୊ ∙ ܫ߬, where ݉ி௔௥. is the calculated mass gain, M is the molar mass, z is the valency number, F is the Faraday constant, I is the current, and τ is the total electrolysis time). 2.3. Elemental analysis and characterization The leachate collected after PCB powder dissolution in HNO3 was filtrated for separation from H2SnO3 and other residues, followed by elemental analysis using X–ray fluorescence (XRF) and Atomic absorption spectroscopy (AAS) techniques. The XRF analysis was conducted on SPECTRO XEPOS XRF Spectrometer in the Center of Analytical Services and Exprimentation of Hochiminh City (CASE). The AAS determination of Cu and Pb content was performed on AAS spectrophotometer from the Laboratory for Analytical Chemistry (Hochiminh City University of Science). Another volume of leachate was analyzed for iron content using AAS technique to determine the efficiency of the magnetic iron separation. Phase compositions of the electrodeposited metals were identified by X–ray diffraction method on Bruker XRD–D8 Advance in the Center for Innovative Materials and Architectures (INOMAR) of Ho Chi Minh City. 3. RESULTS AND DISCUSSION 3.1. Metal composition of the PCB scrap Considering the material composition, e–waste can be defined as a mixture of numerous metals and alloys, particularly copper, lead, aluminum, steel, etc. alongside the various types of ceramics and plastics [10]. To clarify the metallic composition, the PCB scrap was dissolved in 6M nitric acid as described in 2.1 and its leachate was analyzed by XRF technique. The analyzed results were calculated as percentage to initial PCB scrap mass and presented in Table 1. Table 1. Metallic composition of PCB leachate (%). Element Si P K Ca Ti V Cr m (%) 0.0020 0.00023 0.0244 0.0132 < 0.0006 0.00025 0.00021 Element Mn Fe Co Ni Cu Zn As m (%) < 0.0011 0.0086 0.00082 < 0.00071 5.552 0.05287 < 0.00065 Element Zr Mo Ag Cd In Sn Sb m (%) 0.020 0.0110 < 0.0016 < 0.0017 0.0022 0.01349 < 0.0034 Element Te Ba Hg Tl Pb Bi Sr m (%) < 0.0047 0.0260 < 0.00079 < 0.0025 2.596 0.01048 0.00248 oc ma Ot dat iro ele lea ele C ext tec 3.2 we (T cle Data liste curred in co terial is prev her element a reported b Simultane n, copper an ctrolysis ste d compared ments occur Element oncentration ( The analy racted from hnical and e . Investigat To define ll as to the able 2). Figure The cycli arly shows t d in Table 1 nductive tra iously remo s in Table 1 y others auth ously, AAS d lead in le p. Results p to iron, wh red at unsign Table mg/L) tical results discarded conomical p ion of electr the electrod simulated s 2. Cyclic volt c voltammo wo distinct show high ites and lea ved from le are quantif ors, namely analysis w achate. The resented in T ich proved ificantly low 2. Results of Fe 3.25 show a sig PCB scraps oint of view odeposition eposition pa olutions pre ammogram re gram in Fig peaks at –0. content of c d is used in achate after ied in minu 3.4 to 10% as also appl se values we able 2 refle an effective content an leachate’s an nificantly h , the recov . process rameters, C pared with corded for m ure 2, recor 25 V and –0 opper and le tin–lead so filtration in t te contents. for copper a ied to determ re necessar ct a prefera method for d were not i alysis by AA Pb 5,901.88 igh content ery of whic V and LSV copper and ixed copper a ded for the .47 V at cat Tran Th ad in wasted lder. Tin as he form of H These data nd 0.2 to 1.0 ine the exa y for calcula bly higher c separation nvestigated f S technique. of copper h is worth were applie lead conce nd lead soluti mixed copp hodic branc i Phuong Th PCB, wher a common 2SnO3 prec are compara % for lead ct concentr tion of effic ontent of co of iron fillin urthert in th Cu 12,796.60 and lead in considering d to PCB le ntrations in on (Ag/AgCl er and lead h, characteri ao, et al. 133 e copper welding ipitation. ble with [10]. ations of iency of pper and g. Other is work. leachate from a achate as leachate ). solution, zing two Co 13 spe Th res ran hig sol ob in an ste sur pro sec (iv on at pper and lea 4 cific reactio e reversible ults also sh ge around – Theoretic h hydrogen utions with tained only u the aerated odically form ps: (i) the e face; (ii) th duct of Pb( ond electron ) the latter d This prop both electro 2θ = 43.5°, d recovery ns of lead a reactions ar ow high sel 0.25 V SCE ally, the sta overpoten a cathodic e nder fast CV mixed solu ed. Accord lectron tran e nucleus in III) (e.g. Pb , forming P ecomposes t Figure 3 osed mecha des after ele 50.6° for co from discard nd copper c e revealed fo ectivity of c deposition p ndard potent tial, this m fficiency app scanning ( tions, metall ing to Velich sfer and gen teracts with (OH)2+ type b(IV) comp o form PbO2 . XRD patter nism was pr ctrolysis. X pper (JCPD ed printed c ations reduc r the anodic opper reduc otential. ial for lead etal can ea roaching 10 50 mV/s). In ic copper is enko et al. eration of lead ions, ); (iii) the ounds assoc . ns of cathodic actically con RD patterns S card No. ircuit boards tion (Cu2+ + branch with tion if cath in aqueous sily electro 0 % as reve practical co cathodical [12], lead di oxygen–con forming an product is o iated with o (a) and anod firmed by X presented in 04–0836) in by electrolys 2e  Cu a oxidation p odic reactio solutions is deposited f aled on CV nditions, du ly deposited oxide is form taining nucl oxygen–con xidized, wit xygen (e.g. P ic (b) product RD analysi Figure 3 sh the cathodi ing leached nd Pb2+ + 2 rocesses [1 n is conduc – 0.12 V a rom strongl scans. These e to slow ele and lead d ed by the f eus on the taining inte h the transf bሺOHሻଶଶା ty s. s of product ow diffracti c product an solution e  Pb). 1]. These ted in a nd under y acidic data are ctrolysis ioxide is ollowing electrode rmediate er of the pe); and s formed on peaks d 25.5°, 32 car for of for cop of is p lea lea Th cop cat of fur .0°, and 49.5 d No. 37–05 To clarify med after th both produc Clearly, t copper and per purifica Figure 4. X On the ba lead and cop arallely rem d dioxide an d nitrate, co e obtained v The turni per–lead m hodic curren current den ther investig ° for β–PbO 17) in the an the necess e first step a ts were comp he XRD pat the addition tion. RD patterns f sis of these per was def oved by cat d metallic c pper nitrate, oltammogra ng points o ixed solutio t density fo sity were va ation of the 2 (JCPDS c odic produc ity of the s nd second st ared in Figu terns for pro al second el or the produc preliminary ined: lead ca hodic depos opper remov and for their ms are prese f potential ns (Figure 5 r both soluti ried in a ra electrolytic ard No. 14– t. econd step ep of electro re 4. ducts of two ectrolysis ste ts after first (a data, the po n be anodic ition as pure al, LSV sca mixed solu nted in Figu sweep scan ). This pote ons. Similar nge of 30 to process. 4192) and 3 of copper c lysis were a processes w p in Figure ) and second ssibility of ally deposite metal. To id nning was c tions in a po re 5. are consiste ntial value i scans were r 40 mA/cm Tran Th 6.5°, 52.0° athodic dep lso examine ere similar 1 may not b (b) step of ca electrochem d in the diox entify electr onducted fo tential wind nt at –0.30 s equivalent epeatedly p 2 and this r i Phuong Th for α–PbO2 osition, the d. The XRD at 2θ = 43. e required fo thodic depos ical recover ide form an olytic param r separately ow of –0.9 t 6 V for co to 38.34 m erformed an ange was ch ao, et al. 135 (JCPDS products patterns 5°, 50.6° r further ition. ing route d copper eters for prepared o –0.1 V. pper and A/cm2 of d all data osen for Co 13 the eff sum we Dc Eff Da Eff an mA ran ne va com eff pper and lea 6 Selective electrolytic iciencies ob marized in re calculated Figure 5. Tab (mA/cm2) iciency (%) Ta (mA/cm2) iciency (%) The catho d tend to de /cm2. In co ge with a s cessary curre lues of the p Copper an pared to ectively reco d recovery and effectiv parameters tained by co Table 3 and by Faraday LSV course fo le 3. Relation 9 ble 4. Relatio 8 dic depositi crease with ntrary, lead harp rise is nt density c roduct to be d lead are p other metal vered from from discard e removal o defined fro nventional w Table 4. Th law. r the mixed ( between cath 30 7.61 n between an 30 2.72 on efficienci increasing recovery e observed a an be select recovered on 4. resented in ’s constitue their acidic ed printed c f metals from m above ch eight gain e theoretical LSV–HH) an odic current d 35 95.40 odic current d 35 83.80 es reported current dens fficiencies a t 50 mA/cm ed dependin each electr CONCLU discarded P nts. Based leached solu ircuit boards PCB leach osen data. T method and copper and d separate co ensity and co ensity and le in Table 3, a ity in the in re increased 2 current de g on efficien ode. SIONS CB scraps w on these re tions by elec by electrolys ate has been he relation the applied lead content pper and lead pper removal 40 91.91 ad removal ef 40 84.96 re considera vestigated r with curre nsity (Table cy requirem ith substant sults, copp trodepositio ing leached conducted between ele current den s as stated in nitrate soluti efficiency. 5 92 ficiency. 5 96 bly high abo ange from nt densities 4). In prac ents, consid ially higher er and lead n. solution based on ctrolytic sities are part 2.2 ons. 0 .43 0 .59 ve 90 % 30 to 50 in same tice, the ering the contents can be Tran Thi Phuong Thao, et al. 137 A preliminary procedure of the recovery process is proposed with the following steps: disposal of the mounted electrical elements, cleaning, grinding, iron separation for grains screening, metal dissolution, and electrolysis. Copper and lead were recovered using electrochemical technique from discarded PCB scraps. 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