The microstructure and electrochemical properties of Al/Pb-Ag anode. for zinc electrowining1

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1 The microstructure nd electrochemicl properties of Al/P-Ag node for zinc electrowining1 Zhng Yongchun*, Guo Zhongcheng Deprtment of Mechnicl Engineering, Boji Uniyersity of Arts nd Science, Shnxi Boji 71013, Chin Kunming Hender Science nd Technology Co. Ltd, Kunming , Chin Keywords: glvnosttic deposition; energy consumption; node potentil; zinc electrowinning Astrct:Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes were successfully otined y electrodeposition from methnesulfonic cid. The reltion of silver content(y/m% 104) in P-Ag cotings nd Ag+ concentrtion(x/mgdm-3) of electrolyte ws y = x. The results of node polriztion curves nd Time-Potentil curves showed Al/P-0.75%Ag-0.03%Co hd the lowest energy consumption nd node potentil during zinc electrowinning. Introduction Recent yers hve seen extensive studies of luminum sustrte composite nodes used in zinc electrowinning, s seen in[1-3] nd reference therein. The Al/α-PO, Al/β-PO nd Al/P-PANI-WC composite nodes re reltively low in cost nd node potentil during zinc electrowinning for their cotings nd sustrte, ut the service time of them re not stisfied due to the indingforce etween luminum sustrtes nd α,β-po coting, nd higher corrosion rte of P-PANI-WC coting during zinc electrowinning. Led nodes with silver content of out 0.5%-1% re used in zinc electrowinning. To sve silver it s suggested tht P-Ag lloy with out %Ag nd thickness of μm s the ctive node surfce on led node will suffice. Deposition of P-Ag lloys from cynide-free electrolytes ws lso investigted. Electrolytes using potssium hexcynoferrte(п), K4Fe(CN)6, nd polyethylenepolymines s complexing gents were tested[4,5]. In this communiction, we report the preprtion, properties nd microstructure of Al/P-Ag nd Al/P-Ag-Co nodes with unusul chrcteristics. P-Ag nd P-Ag-Co cotings hve different microstructure nd its oxygen evolution potentil nd energy consumption re lower thn conventionl P-Ag node. Experimentl detils The electrolytes contined mol dm-3 led methnesulfonte, 0.5-mmol dm-3 silver methnesulfonte, 0-0mmol dm-3 colt methnesulfonte, 0.5-mol dm-3 methnesulfonte cid, 10-30μmol dm-3 polyvinylpyrrolidone, mol dm-3 sulfoure. All chemicls were nlyticl regent grde from Aldrich nd Fisher. All solutions were prepred with ultr-pure wter. Electrodeposition ws conducted t ph vlues in the 1.5- rnge, t cthodic current density of J=1 Adm-, nd with mechnicl uling for 4 h t 40 C The uthors - Pulished y Atlntis Press 161

2 The luminum sustrtes were pretreted y uffing(mechnicl uffing with fire grinding wheel), degresing (sok in ftty lcohol-polyoxyethylene ether degreser t 40 for 4-1h), custic wsh (sok in 0.3mol dm-3, solution t 0-40 for seconds), cid pickling(0.4mol dem-3 sulfuric cid t 0-40 for seconds), zinc immersion (sok in 0.3mol dm-3, 0.5mol dm-3, 3mmol dm-3 sodium potssium trtrte, 0.5mmol dm-3 iron chloride hexhydrte solution t 0-40 for 60 seconds), cid pickling(3-10s), zinc immersion (t 0-40 for 50 seconds) nd nickel electroplting for 1 minute. All electrochemicl mesurements were mde with electrochemicl worksttion (CHI760C) with three electrode systems. A following set-up ws used: ZnSO4-HSO4 system, 0.9mol dm-3 Zn+, 1mol dm-3 sulfuric cid nd temperture (35 C). The counter electrode ws pltinum plte nd the reference electrode ws MSE with potentil of EMSE= V. The three nodes were used s working electrodes fter 4h of nodic polriztion. Microstructure chrcteristion were crried out using scnning electroscopy (Sirion00SEM, FEI), 30ke ccelerte voltge nd 1 minutes collection time. Result nd discussion P-0.8%Ag lyer ws deposited from solution contining 1mol dm-3 led methnesulfonte, 1.4mmol dm-3 silver methnesulfonte, 1.mol dm-3 methnesulfonte cid, 0μmol dm-3 polyvinylpyrrolidone, 0.3mol dm-3 sulfoure. P-0.75%Ag-0.03%Co lyer ws deposited from solution contining 1mol dm-3 led methnesulfonte, 0.5-mmol dm-3 silver methnesulfonte, 1.mol dm-3 methnesulfonte cid, 0-0mmol dm-3 colt methnesulfonte, 0μmol dm-3 polyvinylpyrrolidone, 0.3mol dm-3 sulfoure. 90 Ag Ag,m%=y Ag, mg/l Fig.1The influence of Ag+ concentrtion of electrolyte on Ag content of P-Ag composite cotings Fig.1 reports the influence of Ag+ concentrtion of electrolyte on Ag content of P-Ag composite cotings. It s found tht Ag+ of electrolyte need supplement pure hour. The reltion of Ag content of P-Ag cotings nd Ag+ concentrtion of electrolyte is eqution (1): y = x, (1) There y represents Ag content of P-Ag cotings nd x represents Ag+ concentrtion of electrolyte. The error limit of eqution (1) versus the true vlue of Ag content(m%) of P-Ag cotings is ±0.03. Fig. presents the node polriztion curves for the Tfel nlysis of P-0.8%Ag, Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes crried out zinc sulphte electrolyte. The prmeters of oxygen evolution dynmics re listed in Tle The uthors - Pulished y Atlntis Press 16

3 .05 1-P-0.8%Ag -Al/P-0.8%Ag 3-Al/P-0.75%Ag-0.03%Co Fitting liner1 Fitting liner.00 Potentil,Evs.MSE log(i/cm ) Fig. Tfel nlysis of P-0.8%Ag, Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes Tle 1 OER dynmic prmeters of P-0.8%Ag, Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes Fitting line Fitting line i 0 /( Acm ) η (i = 0.05 Acm ) / V 1 Anodes i10 i0 P-0.8%Ag Al/P-0.8%Ag Al/P-0.75%Ag-0.03% 0.70 Co 9 The nodic polriztion curve [6]: for Tfel nlysis ws corrected y using the following formul E = Eppl - irs, () There E is the rel potentil vlue of OER, Eppl is the pplied potentil, i is the frdic current, nd Rs is the uncompensted electrolyte resistnce[7]. Fig. shows the ir -corrected Tfel lines of P-0.8%Ag, Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes on stle nodic lyers fter 4 h of nodic polriztion. All lines presented doule-slope ehvior. Bsed on the OER mechnism, the doule-slope vlues nd potentil intercepts of the two lines were seprtely nlyzed y using Origin softwre. The over-potentil η under specific current ws clculted with Tfel sed on the following formul [6]: η = + log i, (3) where nd re constnts, i is the electrode surfce current density, nd η is the OER overpotentil. nd re otined through liner fitting of the plot η versus log i, where = i - E. Compring the Tfel nd the Butler Volmer formuls in the high nodic polriztion region, we cn express the exchnge current density i 0 s follows: 015. The uthors - Pulished y Atlntis Press 163

4 log i 0 = -, (4) where i 0 is the exchnge current density, i is the experiment current, i is the intercept vlue otined with Origin, nd E is the stndrd potentil. Generlly, the vlues of i 0 for OER re negligily smll nd often considered meningless in evluting the electroctlytic ctivity of node mterils. As result, the OER overpotentils η re identified s one of the mjor criteri. The η of Al/P-0.75%Ag-0.03%Co nd Al/P-0.8%Ag nodes lower thn P-0.8%Ag node which indictes tht the two nodic lyers re preferle to OER. In ddition, Al/P-0.75%Ag-0.03%Co nd Al/P-0.8%Ag nodes present higher 1 nd, proly ecuse of the impeded mss nd chrge trnsfer in the micropores nd its microstructure tht is prone to O evolution [8-9] Potentil,V/vs.MSE () 1.44 () 1.4 (c) Time/h Fig.3 Time-Potentil curves crried out n electrolyte contining 0.9mol dm-3zn+ nd 1.5mol dm-3hso4. () Conventionl P-0.8%Ag node, () Al/P-0.8%Ag node (c)al/p-0.75%ag-0.03%co node Fig.3 shows the node potentils with time for the zinc electrowinning tested. P-0.8%Ag, Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes hve high node potentil nd decrese shrply t the first eginning zinc electrowinning, which is due to the dissolution of non-conducting phse of PO nd PO. Then the node potentils decrese slowly which is due to the intermedite product of PSO4 nd PO. After h of zinc electrowinning, the node potentils remined constnt, showing tht the three nodic lyers minly composed of β-po[10],. Compred with P-0.8%Ag node, the node potentil of Al/P-0.8%Ag is decresed y 10mv nd Al/P-0.75%Ag-0.03%Co node is decresed y mv. 3.4 Mechnism of Co on ctivity () () 1um 1um Fig.4 Fruit surfce microstructure. () Al/P-0.8%Ag node ()Al/P-0.75%Ag-0.03%Co node 015. The uthors - Pulished y Atlntis Press 164

5 Fig.4 shows the fruit surfce microstructure of Al/P-0.8%Ag() nd Al/P-0.75%Ag-0.03%Co() nodes. As shown in Figs. 4 nd 4, the size of led crystls on the Al/P-0.75%Ag-0.03%Co node is smller thn tht of crystls on the Al/P-0.8%Ag node. The silver on the fruit surfce of the Al/P-0.75%Ag-0.03%Co node is uliformed, nd the silver crystls re ttched to the surfce of the led composite coting (Fig.4). However, the silver on the fruit surfce of the Al/P-0.8%Ag node hs n ellipticl shpe nd the silver crystls re covered with led (Fig.4). The different crystl sizes of led, s well s the shpe nd existing wy of silver, re proly cused y the existence of colt in the P-0.75%Ag-0.03%Co composite coting. Conclusions Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes hve otined y non-cynide electrodeposition from electrolyte. The results of tfel nd time-potentil nlysis show tht Al/P-0.8%Ag nd Al/P-0.75%Ag-0.03%Co nodes hve lower node potentil s compred to conventionl P-0.8%Ag node for zinc electrowinning. The ctlytic processes of Co on the surfce of the Al/P-0.75%Ag-0.03%Co node during zinc electrowinning cn e descried y the following rection: Co Co + Co 3+. Acknowledgment Finncil supports for this work from the Boji science nd technology project(14gygg--4) References B. Chen, Z. Guo, H. Hung, et l. Effect of the current density on electrodepositing lph-led dioxide coting on luminum sustrte[j]. Act Metllurgic Sinic, 009, (5): Chen Z, Wu J, Guo Z C, et l. Influence of Fluoride Ion on the Electrochemicl Properties of Al/β-PO Electrode[J]. Advnced Mterils Reserch, (01) R. Xu, L. Hung, J. Zhou, et l. Effects of tungsten cride on electrochemicl properties nd microstructurl fetures of Al/P-PANI-WC composite inert nodes used in zinc electrowinning[j]. Hydrometllurgy, 01, 15(8)(01)8 15. Y. Zhng, R. Hu, R. Xing. Electroplting Hndook. Ntionl defense industry press[m]. 011, G. I. Ostpenko. Electrochemicl rections t copper electrode in copper-conducting solid electrolytes[j]. Russin Journl of Electrochemistry, 43(4)(007) Y. Li, Y. Li, L. Jing, et l. Electrochemicl ehviors of co-deposited P/P MnO composite node in sulfuric cid solution Tfel nd EIS investigtions[j]. Journl of Electronlyticl Chemistry, 671(5)(01)16 3. Frnco Silv D V, D Jrdim L M, et l. Influence of the electrolyte composition on the kinetics of the oxygen evolution rection nd ozone production processes[j]. Journl of the Brzilin Chemicl Society, 17(4)(006) L. M. D. Silv, L. A.D. Fri, J. F. C. Boodts. Electrochemicl ozone production: influence of the supporting electrolyte on kinetics nd current efficiency[j]. Electrochimic Act, 003, 48(003) R. Kötz, S. Stucki. Ozone nd oxygen evolution on PO electrodes in cid solution[j]. Journl of Electronlyticl Chemistry & Interfcil Electrochemistry, 8(1)(1987) ) Sirés, C. T. J. Low, C. Ponce-de-León, et l. The deposition of nnostructured β-po 015. The uthors - Pulished y Atlntis Press 165

6 9. cotings from queous methnesulfonic cid for the electrochemicl oxidtion of orgnic pollutnts[j]. Electrochemistry Communictions, 1(010) E. K. Almdri, D. Drvishi, M. S. Khoshkhoo, et l. On the wy to develop co-contining led nodes for zinc electrowinning[j]. Hydrometllurgy, 119 (5) (01) The uthors - Pulished y Atlntis Press 166