AU538112B2 - Aqueous electrowinning of metals - Google Patents

Description

*0 .4 I \~f (a) CON VENTI ION

-4

W we PAUL H. VINING, JACK A.-SCOTT AND PAUL F. DUBY

1n~ of 1220 Lee Drive, Coraopolis, Pennsylvania Saddress(es) United States of Amei.Lca; 456 Riverside Drive, applicants New York, New YoAd; United States of America and 560 Riverside Drive, New York, New York, United States of America. hereby confirm the intention that the International Application identified below proceed F :..(&~Delete one as an application under the Act for the grant of a Standard/pt4yr Patent for an invention entitled

Insert TITLE AQUEOUS ELECTROWINNING OF METALS of invention

(~Insert one number The International Application is (g Australian No:6 7836 /Ez1 only, preferably International No.: PCT/US8-1/00076 the Australian number WIPO No.

('Note: The f ollowing applies ordy to;4eyvekIrd~wM1V_"

Tl_ International Application claims priority from:

Application No. Country *(*insert number, country and filing date for 113, 761 the/or EACH basic application OF Ai 'ERICA January 21., 1980

1I SEP 1961 Ac dess for Service: PHILLIPS ORMONDE AND FITZPATRICK

I Pebo m Patent and Trade MY.ark Attorne~ys 367 Colfins Street Melbourne, Australia 3000 (i),Insert DATE iF fee MyAi V7A, OF of signing

Signature of applicant(s) M '7 1Dated '10 September, 1981 (For body corporate see headnote) WPHILLIPS CRMONL)E PF 7T% ATR 1CK Corporate seal Attor-e,s for: T-ArtT 2 ITT ;P 7" if any r, U 11. V.LiV.L'4V 7

Note: No legalization AIJDJ Djy; or other Witness required

11CPHILLIPS ORMONDE AND FITZPATRICK Patent and Trade Mark Attorneys 367 Collis Street Melbour~ie, Australia

A

AUSIALIA Patents Act

DECLARATION FOR A PATENT APPLICATION

1 Insert "Corwentlon' In support of the (a) .ajrplication made by if applicable (Cb), Insert F=L nalne(s) Paul H. Vining, Jack A. Scott and Paul F. Duby Of applicant(s)

insert "'of Adition" (hereinafter called "applicant(s) for a patent (c) for an If applicabla Insert r'SLtB of invention entitled (d) invention AQUEOUS ELECTROWINNING OF METALS

Insert FULL 2aea AND) addr.ss(ea) of(5 WE'We) Paul H. Vining, 1220 Lee Drive, Corao *oolis, PA 15108 USA; declarant(s) Jack A. Scott, 456 Riverside Drive, New York, NY 10027 (See bcadnote*) USA; and Paul F. Duby, 560 Riverside Drive, New York, NY 10027 USA do solemnly and sincerely. declare as follows: 1. IESM/We are the applicant(s). (or, in the case of an application by a body corporate)

2. IcxM/We are the actual inventor(s) of the invention. (or, where the applicant(s) is/are not the actual inventor(s)) KO nL ame(%) 2. (f) ot

i. Wv xlcite how appli- cant(a deriv(S> 4acts-ttpert -whch--the- -applcaft(s) title mata s.eeenfided- to-mtke-ther -application -are- -as- f uhuws.-

0

(No' e: Paragraphs3 and 4 apply only to Convention applicationT) filingdte an 3. The basic application(s) for patent or similar protection on which the application is based baaic applicrut(s) for the/or EACH is/am identified by country, fing date, and basic applicant(s) as follows: 1y.c aplication. (h) United States of Axtterica, January 21, 1980 Application No. 113,761 P. H. Vining, J. A. Scott and P. F. Duby 4. The basic application(s) referred to in paragraph 3 hereof was/were the first application(s) made in a Convention country in respect of the invention the subject of the application.

Insrt PLACE of Declared at Wk Insert DATE of Dated I

S~naurcs)of (in ).n iii PA@cimNo.-I o II

qaitvd To: The Commissioner of Patents

I PIS17/78 I PEKLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne, Australia

_~a

(12) AUSTRALIAN PATENT ABRIDGMENT (FOLLOWING MODIFIED EXAMINATION BASED ON US PATENT NO. 4279711) (19) AU (11) AU-B-67836/81

(54) "AQUEOUS ELECTROWINNING OF METALS" PAUL H. VINING, JACK A. SCOTT, PAUL F. DUBY (87) WO 81/02169 (21) 67836/81 538112 (22) 21.1.81 (24) 21.1.80 (31) 113761 (32) 21.1.80 (33) US (43) 17.9.81 (44) 26.7.84 (51) 2 C25C 1/08 C25C 1/12 C25C 1/16 C25C 1/10 1/22

(74) PO (56) US 3103474 (57) Claim 1. A method for aqueous electrowinning of a metal, said method including the steps of immersing an anode and a cathode in an electrolyte solution; said solut:Dn comprising water, ions of said metal, and a fuel which is soluble or which can be dispersed in the electrolyte and which will bt oxidized at the anode; said anode having a cata- lytically active surface for the promoting of the reaction of said fuel; passing a direct electric current through said solution thereby to deposit said metal on said cathode, and periodically re- versing or interrupting said electric current for a period of time less than 10% oi the time the electric current is passed in the direction to deposit said metal on said cathode, the time be- tween each of said periodically reversing or interrupting said current being from 30 seconds to minutes so as to cause the reaction at the anode to be substantially

I? limited to the electro- oxidation of said fuel.

27 1

B 1;~5(36)126

AU-AI 678 3 8t PCT WORLD INTELLECTUAL PROPEPTY ORGANIZATION International Bureau

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) I S(51) International Patent Class!fcation 3: (11) International Publication Number: WO 81/02169 I AlI 1/00, 1/08, 1/12, 1/16 (43) International Publication Date: 6 August 1981 (06.08.81) I i i i (21) International Application Number: PCT/US81/00076 I (81) Designated States: AT (European patent), AU, BR, CH (European patent), DE (European patent), FI, FR(Eu- (22) International Filing Date: 21 January 1981 (21.0-.81) ropean patent), GB (European patent), JP, LU (Euro- pean patent), NL (European patent), SE (European patent), SU. (31) Priority Application Number. 113,761 (32) Priority Date: 21 January 1980 (2 1.01.80) Published With internationalsearch report (33) Priority Country: US

Applicants; and (72) Inventors: VINING, Paul, H. [US/US]; 1220 Lee Drive, 0. Coraopolis, PA 15108 SCOTT, Jack, A. [US/ C

r S S US]: 456 Riverside Drive. New York, NY 10027 (US). DUBY, Paudl, F. [US/US]; 560 Riverside Drive, New S York, NY 10027 (US). ga La

o S toe 1 7. 9:81, (74) Agent: CLARK, Richard, Brumbaugh, Graves, Dono- S hue Raymond, 30 Rockefeller Plaza, New York, NY AUSTRALIAN 01 10112 (US). S

0 17 AUG 1981 1 PATENT OFFICE

(54) Title: AQUEOUS ELECTROWINNING OF METALS SeeS

0 Abstract

An improved process for aqueous electrowinning of metals, using methanol (or another soluble fuel) added to the elec- trolyte, a catalytically active platinum mesh or platinum-plated titanium anode and periodic current reversal in order to main- *tain a low anodicpotential, and hence, a cell voltage and energy consumption lower than in conventional processes. Examples i- lustrate the electrowinning of zinc and copper from sulfuric acidsulfate electrolytes, but the process applies to other metals. Also disclosed is the use of an ion-exchange membrane in combinaLon with the above features, in order to decrease the loss of fuel from the anolyte and to minimize the effect at the anode of impurities present in the catholyte.

IS

r IS .1.

-PPPY~L~~flr~n~U~

53- 12 AQUEOUS ELECTROWINNING OF METALS Electrowinning from aqueous solutions using in- soluble anodes is a well-established process for metals like zinc, copper, nickel, cobalt, cadmit'., manganese and others. The metal is electrodeposited at the cathode from a solution of one of its salts, most commonly a sulfate. Water is decomposed at the anode, usually made of lead or a lead alloy; oxygen is evolved and acid (hydrogen ions) is formed. The elec- trowinning reactions may be described generally by the 6O 6

following (wherein M represents any of the metals men- 6 tioned above): 6~

6 Cathode: M 2e M Anode: H20 2 2H 2e 6 Overall Reaction: M H2 0 02 2H+ M For a sulfate solution, the overall reaction can be written: 66 6 1 MSO 4 H20 -02 H 2 SO M

0 20 The minimum electrical energy consumption for the 6* electrolytic process is proportional to the reversible 6 6 electromotive force (emf). The actual energy used corresponds to the operating cell voltage which is the sum of the reversible emf plus irreversible potential 6 25 differences, namely the ohmic drops, and the anodic and cathodic overpotentials. The typical voltage components, as disclosed by A. R. Gorden, "Improved fesour-c.es Use of Raw Material, Human and Energyj~easourch in the Extraction of Zinc," in Advances in Extractive Metallurgy 1977, edited by Jones, Institution of Mining and Metallurgy, London, p. 158, of a zinc electrolysis cell are as follows:

'I. 7,,3E r/ l i

HIIWRnri t;MtrrUa~*iLdrJr*V-irxcirrr

Volts Reversible cathode potential vs. SHE 0.819 Cathode overvoltage -0.062 Addition agent effect, etc. 0.001 Cathode potential, sum of above three -0.,882 Reversible anode potential vs. SHE +1.217 Oxygen overvoltage +0.84 Addition agent effect, etc. -0.216 Anode potential, sum of above three +1.843 Anode scale potential drop 0.15 Electrode potential drop U.5 9 4 Total ohmic effect, sum of above two 0.744

Total cell voltage 3.467 Conditions:

Cathode current density 526 A/m 2 Zinc in electrolyte 44 g/l H 2SO 4 in electroly.e 99 g/l Mn in electrolyte 11 g/l Co in electrolyte 10 mg/l Pure lead anodes Addition agents Glue 25 mg/l Beta-naphthol 25 mg/ Sb 0.15 mg/1 Electrode spacing 3 in cathdde centre- cathode centre an-rguua]e& i- also inorcl' proportion----- al- to t electrochemical current efficiency. In a typ- icUl moder lant, the average current efficiency is 90% and the ene consumption is 1.4 kWh/lb. In order to redu these energy requirements, there has been developed ac ding to the present in- vention a method of electrowinnin getals employing a fuel which can react electrochemically the anode. This improved method includes the use of a c yt- ically active anode (necessary to promote the fuel--- -elocro-oxidiation) as well as the use_of periodic

iA IjiREA U

7 1il F

Cathode: 3M+++6e 3M Anode: CH 3 OH+H 2 0 4* C 2 +6H +6e Overall Reaction: CH..OH+H 3M+C02 +6H+ 2

The actual energy use is also inversely proportiona2 to the electrochemical current efficiency. in a typical modern plant, the average current effic;.ncy is 90% and the energy consumption is 1.4 kWh/lb. Zn. In order to reduce these energy requiremients, there has been developed according to the present invention a method of electrowinninq metals employing a fuel which can Ce.. 10 B. ow react electrochemically at the anode. This improved method Be S includes the use of a catalytically active anode (necessary 00 C 06 to promote the fuel electro-oxidation) as well as the use of BC '0 B.. periodic 0g B. Soot,

WO B

Qr 4' C

-S

2a k~ ~t.

b-0

WO 81/02169, PCT/US81/00076

Z -3-

current interruption (PCI) or, preferably, periodic current reversal (PCR) in the electrolysis cell. The invention preferably also includes but does not require the use of a diaphragm or an ion-exchange membrane to separate the anolyte from the catholyte thereby allowing a higher concentration of the fuel near the anode, where it is used, than near the memrn-ane cathode. The diaphragm or(mambrane also decreases the transport to the cathode of catalyst platinum) which could be removed from the anode, and the transport to the anode of impurities chloride ions) in the catholyte which could hinder the fuel oxidation. According to the present invention, the oxidation 15 of water at the anode in conventional systems is 0s. replaced by the oxidation of a fuel, preferably one which is soluble methanol) or which may be dispersed in the electrolyte hydrogen). The oxidation of methanol proceeds with the evolution of carbon dioxide gas and the formation of acid (hydrogen ions) from the fuel and water. The reactions involved Smay be summarized as follows: Cathode: 3M++ 6e 3M Anode: CH 3 0H E2 0 CO 2 6H 6e Overall Reaction: CH3OH H2 0 3M 3M CO 2 6H+ As indicated by the following, the anode reaction has a lower reversible emf than that involving water oxidation, and its minimum energy requirement is accordingly lower. a) Traditional zinc electrolysis (water oxidation) 2H2 0 02 4H+ 4e EO 1.229 V b) Proposed Zinc electrolysis with CH30H addition H20 CO 2 6H+ 6e E° 0.043 V Reduction in reversible emf: 1.186 V

*flg~atsasssri.. s'-

'O 81/02169 S PCT/US81/00076

-4-

Taking the typical conventional cell voltage fig- ure above of 3.467, the reduction in voltage relative to the total cell operating voltage 1,186 x 100 3,467 34%.

Methanol is characterized here as a fuel because it is oxidized at the anode. This reaction is similar to the anodic reaction of a fuel cell. As is known and documented in the fuel cell art, the reactivity of methanol in acid media is low and a catalytic elec- trode surface is needed for the reaction to proceed at acceptable rates. The only suitable catalysts found so far are the platinum class metals. Even these metals, however, have contributed to limited success in the past. It is generally agreed that there is a "poisoning" reaction which occurs at the platinum anode, greatly reducing the active sites of methanol oxidation. This "poisoning" reaction is understood to be one of a combination of 1) the adsorption of an intermediate product in the oxidation of CH3 0H, 2) the ad r tin of a side product, or 3) the formation of a platinum oxide on the electrode surface. According to the present invention, the adverse effects of this "poisoning" reaction at the anode is substantially corrected or prevented by pe:iodically interrupting or, preferably, reversing the direct electric current in the electrolysis cell. Thus the anodic sites which have been or otherwise would be Q rendered inactive by the poisoning reaction are main- tained in a catalytically active state. It is contem- plated that the PCI or PCR cycle be relatively short e.g. 30 seconds to about 10 minutes so as to main- tain a relatively constant, and desirably low, cell oi.er voltage. Ine*.ee- words, a feature of the present invention is the discovery that PCI or PCR may be used to maintain the low cell voltages otherwise obtainable for only short periods with fuels such as methanol. Also, while PCI and PCR are both disclosed in the con- text of the present invention, PCR is definitely pre- ferred. In this regard, work has been done in the past e.g. as disclosed by Duby, "Reducing the Specific Energy Consumption in Zinc Electrowinning," Ind. Chim. Belge, Suppl., Vol. 1, pp. 777-781, 1959 and Vereecken et al., "Contribution to the Study of Anodic Oxidation of Methanol in Sulfuric acid in Relation to its Use for Decreasing the Energy Consumption in Zinc Elec- trowinning," ATB Metallurgie (Mons, Belgium), Vol. X, No. 4, pp. 113-124, 1970 -involving the use of fuels 15 such as formic acid or methanol together with current interruption (as opposed to periodic current reversal). This work did not result, as is the case with the present invention, in a method whereby the electrolysis cell could be maintained at a low voltage for substantial lengths of time. To the contrary, the electric current was applied unidirectionally,untiL the poisoning reaction at the anode caused the cell o voltage to rise to unacceptable levels. At this point the system was shut down i.e. the current was inter- rupted to permit the anode to be regenerated. After the anode was regenerated current was applied until the system again became inoperative. Siificantly, there was also a rapid decline in the ability of the anode to become regenerated with the result that even the initial low-high voltage cycle could not be main- tained for any substantial length of time. The use of PCI or PCR in the context of the present invention is also to be distinguished over prior methods wherein PCR was used in electroplating and electrorefining, and was suggested for use in

SU R I 'wC f, 81/02-69 PCT/US81/00076

-6-

conventional zinc electrowinning to improve the cathode deposit and thereby to operate at higher cur- rent densities. Such methods did not take advantage of a fuel-oxidation reaction at the anode and hence were unrelated to the maintenance of anode activity. The present invention may be illustrated by the following exemplary data. Methanol, either anhydrous or as an aqueous mixture, or another pref- erably soluble fuel, is added to the electrolyte. This is preferably accomplished just before the elec- trolyte enters the electrolysis tank or in the tank itself. It can also be added after the leaching, during one of the purification stages, or in the elec- trolyte storage reservoir. The methanol feed rate is such that its concentration in the electrolyte tank is no less than about 0.1M (3.2 g/1) and preferably in a range of about 0.2 to 1.0M, but it can be higher. The zinc concentration is as in a conventional process, typically about 40 g/l up to saturation (about 220 g/1). If a diaphragm or an ion-exchange membrane is used, then the methanol is added to the anolyte and itsFeetcntreti~ e can be controlled more easily. In Sorder to decrease losses, it is preferred that the methanol concentration be kept closer to the lowest value at which the fuel electro-oxidation can be main- tained The anode is made of an electrically conducting material which does not react under aqueous acid oxi- dizing conditions and which has a catalytically active surface. For instance, while platinum class metals and alloys make suitable catalysts, graphite or ti- tanium can be used as a substrate with platinum class metal and alloy surfaces. Other commercially avail- able electrodes can also be used such as those known in the trade as "dimensionally stable anodes" (DSA).

L NREA

h -2

N

.NO 81/01169 PCT/US)RI/00076

The PCI or PCR cycle duration can vary from a few seconds to several minutes or longer. As was ex- plained above, the important consideration here is that the overall cell voltage be maintained at a rela- tively consistently low level i.e. it is not desired that the anode be permitted to become poisoned to a substantial degree before the current is interrupted or reversed. The actual cycle duration utilized in any par- 10 ticular application will depend largely upon the sys- S.

BOOS 6 tem parameters, particularly upon the type of anode mu em em used, In large commercial applications, it is contem- S I plated that anodes can be employed that will maintain a mm cm m 6 substantially high and relatively constant catalytic B EIO 15 activity for several up to 10) minutes before a mm mm. few seconds of PCR need be applied. It is thus not mm *m S a contemplated that a cycle duration of less than 00mm seconds, and preferably one minute, will be necessary or desirable while a duration of longer than minutes and more likely 5 minutes may not be obtain- mm able. The preferred cycle time is,~ therefore, from m~ seconds to 10 minutes and preferably from 1 to mm C minutes. 0 CO@* 60 a It will also be appreciated by one skilled in the art that the duration of current reversal or (op- C tionally but not preferred) interruption should be as 0 m~m mom short as possible (consistent with the maintenance of S mm mm m anodic activity) compared to duration of the electro- mm winning direct current sirnce the reversal period wastes energy and detracts from the overall metal re- covcrv. It is therefore suggested that the perioac f reversal or interruption be less than 10% of the over- all cycle anid preferably less than Indeed, it is contemplated that with high quality anodes, reversals or interruptions of 1% or less may prove sufficient.

QIj 0' 'T

1O 81/02169 PCT/USI/00076

-8-

It will be appreciated from the above that while it is a stated object of the invention to maintain relatively constantly high anodic activity and hence a low cell voltage, there may be a relatively slight cell voltage rise during the PCR or PCI cycle. What is to be avoided are the relatively drastic voltage fluctuations such as would occur when the methanol- oxidation is substantially replaced by the water oxi- dation reaction. Put another way, it is an object of the invention that the reaction at the anode be sub- stantially limited to the fuel electro-oxidation. An ion-exchange membrane can be used to separate the anolyte containing the methanol or other fuel from the catholyte. As a cation-exchang- membrane, fo instance, there can be used a perfluorosulfonic acid resin which has a transport number for hydrogen ion close to unity and a low electrical resistance. The "'1afionG' membranes available commercially are suit- able. An anion-exchange membrane or a porous dia- phragm may not be as effective, but they may be useful in some instances.

EXAMPLE I A batch zinc electrowinning experiment was car- ried out in a one-liter beaker with a 10 cm 2 aluminum cathode and a 10 cm 2 platinized platinum mesh anode, separated by 3.5 cm. The ano'e was prepared by the following procedure: a) cleaning in aqua regia, then o 4 in nitric acid, and then by cathodic hydrogen evolu- tion in sulfuric acid; b) platinizing in chloro- platinic acid with a current of 100 mA for 3 minutes, 200 mA for 3 minutes and 500 mA for 5 minutes. The electrolyte was a solution containing 65 g/l Zn, 100 g/l H2 SO and 32 g/l CH3 0H. The electrodes were mounted in a Plexiglass holder which ensured that the

-CX3I:Atj h 4

'WO 81/02169 PCT/US81/00076

electrodes remained parallel to each other and that the current was efficiently and evenly distributed. The holder was also provided with suitable openings to allow for circulation by natural convection) of the electrolyte. Electrolysis was carried out by passing a currei c of 400 mA for 3.5 minutes at about By means of mechanical timers and swittches, the current was peri- odically reversed according to a cycle of 60 seconds forward current followed by 2.5 seconds reverse cur- .0.0 rent. Thie average anode potential was 0.64 V (rela- ,e 0 tive to standard hydrogen electrode the cell voltage was 1.9 V and the current efficiency was 87.1%. This yielded an electrical energy consumption of 0.81 kWh/lb. Zn.

e Comparative Example la P 0 0 0 Another experiment was carried out under the same conditions as those of Example I except for the fact that the current was 350 mA and it was no; reversed. 0 0 The anode potential started rising to about 0.8 V (SHE) in about 30 minutes and then to 1.8 V 'SHE) a few minutes later.' By interrupting the currer 0 briefly, the anode potential was reduced to 3.b V (SHE), but then it would soon increase again to 1.3 V (SHE) for a cell voltage of about 2.9 V. Comparative Example Ib 00 0 An experiment war carried out under the same con- 00 00 ditions as those of Example Ia except for the fact that the electrolyte contained no methanol. The anode potential was 1.86 V (SHE) and the cell voltage was 2.9 V. Comparative Example Ic An experiment was carried out under the same con- ditions as those of Example Ib except for the fact

CIMFI S. A WIo pp

W 81/02169 PCT/US8190076

that the anode was a sheet of lead instead of a platinized platinum mesh. The anode potential was V (SHE) and the cell voltage was 3.5 V.

EXAMPLE II An experiment was carried out under conditions similar to those of Example I. The anode was made of titanium mesh and it was platinized in a chloro- platinic acid solution as described in Example I. The electrolyte contained 80 g/1 Zn, 100 g/l H 2 S0 4 and 32 g/1 CH30H. A current of 400 mA was passed for 8 hours at 40 C. It was periodically Leversed following a cycle of 60 seconds of forward current and 2.5 seconds of reverse current. The average anode potential was 0.7 V (SHE), the cell voltage was 1.93 V, the current efficiency was 86.9% and the energy consumption was 0.83 kWh/lb,

EXAMPLE III A copper electrowinning experiment was ca;ried out with an electrolyte containing 40 g/l Cu, 30.g/1 H2 S0 4 and 32 g/l CH30H at 40°C. The anode was a platinized titaniu mesh prepared as described in Example I. TheJ heai d was a 13 cm 2 titanium sheet. A current of 250 mA was passed for 8 hours. It was periodically reversed with a cycle of 60 seconds forward current and 2.5 seconds reverse current. The average anode potential was 0.71 V (SHE) and the cell voltage was 1.02 V. The current efficiency was 91.8% resulting in an energy consumption of 0.43 kWh/lb. Cu (compared to about 1.0 KWh/lb. Cu for the traditional process).

EXAMPLE IV A batch zinc electrowinning experiment was car- ried out in a one-liter beaker with a 9.2 cm 2 aluminum

RE.A R- v i H O MPI l l y^T '/^-A-A)tIO cathode separated from a platinized titanium anode by a cation-exchange membrane. The anode was a 0.063 in. thick expanded titanium mesh with a diamond-shaped open area. It was coated with about 20 Pin. of a 70/30 plainum/iridium deposit. It was further covered with platinum black by platinization in a chloro- platinic acid solution, using periodic current reversal, with a current of 350 mA for approximately min. The cation-exchange membrane was a Nafion® ion-exchange membrane, series 427, which is a homog- 10 eneous film, 7 mils thick of 1200 equivalent weight perfluorosulfonic acid resin laminated with a Teflon fabric. The two electrodes and the membrane were placed in a Plexiglass holder inside the beaker to maintain the electrodes at a distance of 6.8 cm from 15 each other. The membrane was fitted in the center of the holder n such a way that it formed with the anode, the walls and bottom of the holder a closed compart- ment for the anolyte of about 30 cm2 useful volume. The catholyte compartment was open in order to allow 20 the circulation of the electrolyte in front o the o. cathode and outside the holder within the beaker. The anolyte was a solution of 32 g/l CH30H and 100 g/l H 2 S0 4 The catholyte had 100 g/l Zn and 100 g/l H2S04. Electrolysis was carried out at 400 C by passing a current of 400 mA for 4 hours, periodically reversed, S following a cycle of 60 seconds forward current and 2.5 seconds reverse current. The average anode po- tential was 0.64 V (SEE), the potential drop across the membrane was 0.24 V, and the ohmic drops across the anolyte and catholyte were about 0.31 V each. The cell voltage was 2.4 V and the current efficiency was 82.6%, yielding an energy consumption of 1.09 kWh/lb. Zn.

UpREAU

WO 81/02169 PCT/US8I/00076

-12-

rhe C/irnzs /Ae rVes,/.o, C. DeL'eA/nAy e PoCs s 1. A method for aqueous electrowinning of a metal, said method including the steps of immersing an anode and a cathode in an electrolyte solution; said solution comprising water, ions of said metal, and a fuel which is soluble or which can be dispersed in the electrolyte and which will be oxidized at the anode; said anode having a cata- lytically active surface for the promoting of thp reaction of said fuel; passing a direct electric current through said solution thereby tc deposit said metal on said cathode, and periodically re- versing or interrupting said electric current for a period of time less than 10% of the time the electric current is passed in the direction to deposit said metal on said cathode, the time be- tween each of said periodically reversing or interrupting said current being from 30 seconds to minutes so as to cause the reaction at the anode to be substantially limited to the electro- oxidation of said fuel.

2. A method for aqueous electrowinning according to claim 1 wherein said metal is at least one of the g. oup consisting of zinc, copper, nickel, cobalt, cadmium and manganese.

3. A method for aqueous electrowinning according to claim 2 wherein the duration of said periodically reversing or interrupting said current is less than 5% of the time between each of said reversing or interrupting said current.

~\JREA S_ .SILV

aiEct~a~s~g~l~a;~N~i~;a~~r:

S WO 81/02169 PCT/US81/00076

-13-

4. A method for aqeuous electrowinning according to claim 2 wherein the time between each of said re- versing or interrupting said current is from 1 minutes to 5 minutes.

5. A method for aqueous electrowinning according to claim 2 wherein the fuel is methanol.

6. A method for aqueous electrowinning according to claim 4 wherein the fuel is methanol.

7. A method for aqueous electrowinning according to 10 claim 5 wherein the metal is zinc.

8. A method for aqueous electrowinning according to claim 6 wherein the metal is zinc.

9. A method for aqueous electrowinning according to claim 2 wherein said reversing or interrupting said current is limited to reversing said current. a S

10. A method for aqueous electrowinning according to claim 9 wherein the step of periodically reversing said current is carried out in cycles of substan- tially equal duration. a S 20 11. A method for aqueous electrowinning according to O 0

claim 2 including the step of including in the electrolyte a diaphragm or membrane to separate the anolyte from the catholyte thereby to permit the concentration of fuel in the anolyte to exceed the concentration of fuel in the catholyte.

CoS'N C::PI ;TE/^

INTERNATIONAL SEARCH- REPORT International Application No P C T/US 8 1/00 0 76 1. CLASSIFICATION OF SUBJECT MATTER (it several classiflcatlon symbols apply, Indicate all) I According to intornationaV Patent Classificatica (IPC) of to both,National Classification and IPC INT. CL3 C25C 1/00, 1/08, 1/12, 1/16 US. CL. 204/105R, 108, 119 If. FIELDS SEARCNHtD Minimum Dccumeritatlon Searched A Classification Grsten Classification Symbols

cis 204/105R 106, 208, 119

Docuimentation Searched other thani Minimum Documentation to the Extent that such Documents are Included In the Fields Searched 6

Ce a a. 0 5000 6* Ce 06 0 Ill. DOCUMENTS CONSIDERED TO BE RLEVANT 14 5 Category" Citation ofOocnment, it with Indication, whore appropriate, of the relevant pacages it Relevant to Clalm No. XI a @0 S S a X iN, IND. Chim. Beige Suppli. vel. 1 c9!), ipp. 777-781, Paul Duby. 'a Experimental Contributicn 4-c t-he Stujy ef .i ~6* a Possible Reduction of the Specific Er~ergy

@0 0 Consumption in Zinc Electrolysis. Abstract, *0 a p. 778 col. 2. X N, ATB Motallurgie, Mons, Belgium Vc! X, ANo 4, 1970, pp. 113-124, J Vereecken et al, ;Con~tribution to the Study of the Anod~c .00000 0 !oxidation of Methanol in Sulfuric Medium lin Relation to its Use for Decreasing Speci- 0 @0 S ~4 a 5* ific Energy Consumption in Zinc Electrowin- ining. Abstract, p. 1:-6 col. Q. 2: col. a a i2, p. 122 col. 1, S A IUS, A, 598,180, Published, '1February :8981 Hoepfner C 0 A IUS, A, 3,103,474, Published, 10 September1 6 11963, Juda Ca 0@ S A US, A, 3,172,003 Published, :3 Ncvember 1 OS j1973, Gordy Special categorias of cited documents: 16 document defining the general sitate of the art document published priorhto the International filing data but earlier documneot but publiahed on or after the International on or altar tha priority date claid filig de. I" later document published on or after the International filing IL' document cited for special reason other than those referred date or priority date and not in conflict with the application, to In the other categories but cited to understand thesprinciple or theory underlying document referring to an oral disclosure, use, exhibition or h neto other moans IX" document of particular relevance IV. CERTIFICATION Data of tha Actual Compe'on of the international Search I -Dae of Mailing of this International Search Report'3

09 APRIL 1981 115 APR 1881 International Searching Authority'I Sltjrature of Authorized Officer 39

ISA/US .M.'7TFRI ELL 0 T. Form PCTIISA/210 (second sheet) (October 1077

International AplIlcation No. PCT/US 831/00076 FURT jR INFORUA~rON CONTINUED FRtOM TH& SECOND SHUET

A IUS, A, 4,056,449, Published, 01 November '17,de Nora A 'US, A, 4,178,218, Published, 11 December 11 1979, Seko A N, J. Of Metals, Vol. 27, No. 12, p. A53, 1,3,4,9,10

A N, Chemical Abstracts, Vol. 87, 1977, 1,3,4,9,10 87 :42299F

a. a e a SCOS V0 ONSERVATIONS WHERE CERTAIN CLAIMS WERE FOUND UNSEARCHABLE If CO CC C Ce This International search report has not been established In respect of certain claim* under Article 17(2) for the following reasons: 4 C e t4] claim numbers.- because they rat'rte to subject matter's not required to be sarchedf by this Authority, narmely: S e a ee Cd e Ce C' ced

a. a a e *e asee 2.C] Claim because they relate to parts of the International application that do not comply with the prescribed require- #mnta lo such an extent that no meanlngtul lnternati~nal search can bii carried out 15. specifically:

e eec... a e ee e 'C cc e

0 e~ee.e a e VI.] OBSERVATIONS WHERE UNGITY OF INVENTION IS LACKING 11

This Intbmatonal Searching Authority found multiple Inventions In this International application aa follows: C C C C. cc C e C e ee cc e Cc a

1.FJ As alt required additional sarch fees were timely paid by the applicant this in rrnstional search r-vport covers all searchable claims of the lnternptional application. 24]1 As only some of the required additional search fees were timely paid by the applicant, this international Search report covers only those clams of the International application for which lees were paid, specifically claims:

if] No requlred additional search fees were timely paid by the applicant. Conseque~tiy, this International starch report Is restricted to the Invention first mentioned In the cla~ims; It Is covered by claim numbers;

Remark-on protest The sddlllarn~ earch foe were accompanied by applicants protest. No protest aeompae the payment of addItional "earch fee.

Form POCTIISAIMtO (supplemental sast (October 1977)

Claims

1. A method for aqueous electrowinning of a metal, said method including the steps of immersing an anode and a cathode in an electrolyte solution; said solution comprising water, ions of said metal, and a fuel which is soluble or which can be dispersed in the electrolyte and which will be oxidized at the anode; said anode having a cata¬ lytically active surface for the promoting of the reaction of said fuel; passing a direct electric current through said solution thereby to deposit said metal on said cathode, and periodically re¬ versing or interrupting said electric current for a period of time less than 10% of the time the electric current is passed in the direction to deposit said metal on said cathode, the time be¬ tween each of said periodically reversing or interrupting said current being from 30 seconds to 10 minutes so as to cause the reaction at the anode to be substantially limited to the electro- oxidation of said fuel.

2. A method for aqueous electrowinning according to claim 1 wherein said metal is at least one of the group consisting of zinc, copper, nickel, cobalt, cadmium and manganese.

3. A method for aqueous electrowinning according to claim 2 wherein the duration of said periodically reversing or interrupting said current is less than 5% of the time between each of said reversing or interrupting said current.

4. A method for aqeuous electrowinning according to claim 2 wherein the time between each of said re¬ versing or interrupting said current is from 1 minutes to 5 minutes.

5. A method for aqueous electrowinning according to claim 2 wherein the fuel is methanol.

6. A method for aqueous electrowinning according to claim 4 wherein the fuel is methanol.

7. A method for aqueous electrowinning according to 0 claim 5 wherein the metal is zinc.

8. A method for aqueous electrowinning according to claim 6 wherein the metal is zinc.

9. A method for aqueous electrowinning according to claim 2 wherein said reversing or interrupting 5 said current is limited to reversing said current.

10. A method for aqueous electrowinning according to claim 9 wherein the. step of periodically reversing said current is carried out in cycles of substan¬ tially equal duration.

2011. A method for aqueous electrowinning according to claim 2 including the step of including in the electrolyte a diaphragm or membrane to separate the anolyte from the catholyte thereby to permit the concentration of fuel in the anolyte to exceed

25 the concentration of fuel in the catholyte.

12. A method for aqueous electrowinning according to claim 5 wherein said methanol is present in a concentration of at least about 0.1M.

13. A method for aqueous electrowinning according to 5 claim 12 wherein said methanol is present in a concentration of about 0.2M to about 1.0M.

14. A method for aqueous electrowinning according to claim 7 wherein said zinc ions are present in a concentration of at least 40 g/1.

10 15. A method for aqueous electrowinning according to claim 2 wherein said catalytically active surface is selected from the group consisting of platinum class metals and alloys.