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Deposition of Nickel-Cobalt Alloys by Controlled-Potential Electrolysis

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Deposition of Nickel-Cobalt Alloys by Controlled-Potential Electrolysis it\ IRIIs931I t Bureau of Mines Report of Investigations/1985 Deposition of Nickel-Cobalt Alloys by Controlled- Potential Elect ro lysis By J. l. Holman and l. A. Neumeier UNITED STATES DEPARTMENT OF THE INTERI OR i /G!1~ J O~ , ~ M,NES ...75TH A~ Report of Investigations 8 9 31 Deposition of Nickel-Cobalt Alloys by Controlled-Potential Electrolysis By J. L. Holman and L. A. Neumeier UNITED STATES DEPARTMENT OF THE INTERIOR Donald Paul Hodel, Secretary BUREAU OF MINES Robert C. Horton, Director Library of Congress Catalog ing in Publication Data: Holman, J. L.(Jame:-; L.) D eposition of n ic'ke I-co ba l tal loy s by Co n trol I ed-puten tial e lectroly si s . (Report of investigations / United States Department of the Interior, Bureau of Mines; 8931) Bibliography: p. 17 . Supt. of Docs . no.: I 28. 23:8931. I. Cobalt-nickel a l loys-Recycling. 2. Scrap metals-Recycling. 3. Electrolysis. I. Neumeier, L. A. II . Title. Ill. Serie s : Report of investigations (United States. Bureau of Mines) ; 8931 . TN23.U43 [TN798] 622s [669'.733] 84-600281 CONTENTS Abstract •................ D ••••• co •••••• coe ••••••••••••••••••••••••••••••••••••••• 1 Introduction ••••••••••••••••••••••••••••••• • eo ., ,.. •••••••••••••••••••• • ••• • ••••••• 2 Experimental equipment and procedure ••••••• 3 Experimental results and discussion • •• •• ••• ·. ..... .... .... .. ..... .... ... .... .. 5 Nickel-cobalt alloy anode •••••••••••••••• ·..................... ............. 5 Nickel-cobalt-chromium alloy anode ••••••• ·.................................. 9 Extended deposition periods ................................•.•............... 11 Chromium additions to electrolyte. o •••••••••••••••••••••••••••••••••••••••••• 13 Effects of pH and stirring rate ••• • •• ••• •• •• ••• •••••• •••• ••• ••••••••••••••••• 14 Effects of high current density •••••••••••••••••••••••••••••••••••••••••••••• 15 3ummal'y and conclus ions •••••• •• •• • .•.•.••• •• • • •••••••••.••..... • ••••••• •• •••.•• 15 Re f erences " (J " .... II . ... .................. 0 ••••••••• • •••••••••••••••••• •• ••••••••••• 17 ILLUSTRATIONS 1- Simplified schematic of apparatus for controlled-potential electrolysis ••• 4 2. Apparatus used fot, electrolytic experiments ••••••••••••••••••••••••••••••• 5 3. Cathode current efficiency versus cathode potential ••••••••••••••••••••••• 7 4. Nickel in alloy deposit versus cathode potential •••••••••••••••••••••••••• 7 5. Cobalt in alloy deposit versus cathode potential •••••••••••••••••••••••••• 7 6. Nickel in alloy deposit versus cathode current density •••••••••••••••••••• 7 7. Cobalt in alloy deposit versus cathode current density •• • ••••••••••••••••• 8 8. Cathode current efficiency versus cathode curr ent density •• • •••••••••••••• 8 9. Cathode current density versus cathode potential •••••• • ••••••••••••••••• • • 8 10. Nickel- to- cobalt de pos ition r a t io versus cathode potent i al •••••••••••••••• 8 TABLES 1. Selec ted standard reduction potentials ••••••••••••••••••••••••••••• • •••• 3 2. Short-term controlled-potential electrolytic experiments •••••••••••••••• 6 3. Long-term controlled-potential electrolytic experiments ••••••••••••••••••• 12 4. Controlled-potential electrolytic experiments with chromium additions ••••• 13 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT A/dm2 ampere per square decimeter L liter A/ft2 ampere per square foot lb pound °c degree Celsius lb/yr pound per year cm centimeter mL milliliter g gram pct percent giL gram per liter V volt h hour wt pct weight percent DEPOSITION OF NICKEL-COBALT AllOYS BY CONTROllED POTENTIAL ELECTROLYSIS By J. L. Holman 1 and L. A. Neumeier2 ABSTRACT The Bureau of Mines is conducting research to improve technology for the recovery of strategic and critical metals, such as cobalt, nickel, and chromium, that are lost in bulk and particulate superalloy-type scrap because it has not been possible to process mixed contaminated scrap efficiently. The research approach involves melting and casting mixed superalloy scrap into soluble anodes for electrodeposition of Ni-Co alloys by controlled-potential electrolysis. The initial experi­ mental results described in this report are from electrolytic tests us­ ing alloy anodes cast from elemental nickel, cobalt, and chromium, the main constituent metals of superalloys. Baseline data and operating parameters are necessary for Ni-Co and Ni-Co-Cr alloys before detailed experiments can be conducted on the more complex superalloy scrap. This basic research assessed the effects of cathode potential, S04:CI electrolyte ratio, electrolyte pH, stirring rate, deposition time, cathode current density, and chromium concentration on cathode current efficiency, alloy deposit composition, and deposition potential at a cell temperature of 55° C. 1Research physicist. 2supervisory metallurgist. Rolla Research Center, Bureau of Mines, Rolla, MO. 2 INTRODUCTION As part of the goal to devise technol­ magnets (e.g., Alnic04 alloys). Sub­ ogy that provides the United States the stantial amounts of grinding sludge are means to meet its strategic and critical generated in magnet manufacture, which mineral and metal needs, the Bureau of are mostly exported for processing. A Mines has been investigating procedures pyrometallurgica1 process for reclaim­ to recover nickel, cobalt, chromium, and ing Co-Ni and other values from con­ other values from mixed contaminated taminated magnet alloy grinding sludge superalloy-type scrap. Development of has been investigated and patented (2). improved recycling technology is one of The process includes initial degreaslng the options available to reduce high and elemental sulfur removal by wash­ reli~nce on foreign sources for these ing in hot perch1oroethylene., screening metals. to remove grinding media, then oxida­ tion roasting in air, and hydrogen re­ A comprehensive study of the domestic duction. The resulting powder product availability of chromium and related cri­ has low enough sulfur and carbon lev­ tical metals contained in six classes of els to be a candidate material for addi­ superalloy scrap material (1) 3 revealed tion directly to permanent magnet alloy that over 100 million lb/yr of mixed con­ melts. taminated superalloy and associated heat­ and corrosion-resistant high-alloy scrap A number of processes for recycling of are downgraded or exported. This scrap nicke1- and cobalt-base alloys or sep­ contains over 20 million lb of potential­ aration and recovery of specific con­ ly recoverable chromium, 5 million lb of stituents have been investigated, but cobalt, and 50 million lb of nickel, plus only a limited number have been used several million pounds of other alloying commercially. elements. Kusik (3) investigated a scheme for Supera110ys and related specialty al­ melt oxidation whereby chromium and iron loys, which comprise the single largest from stainless scrap were oxidized to use category for cobalt, have perhaps the the slag for subsequent reduction to fer­ most stringent specifications of any al­ rochromium; earlier Bureau research had loy group. This stems from their use for demonstrated chromium removal from su­ jet engine and other high-reliance compo­ pera110y scrap by melt oxidation (i). nents where there is little margin for The research of deBarbadi110 led to a error. Producers will not, therefore, combined pyrometal1urgical-hydrometal1ur­ charge any scrap materials into melts gica1 procedure (5) whereby supera110y that do not meet their specific charge scrap was oxidized-and su1fidized under specifications. Because of these re­ controlled conditions; chromium sulfide quirQments, mixed contaminated super­ was roasted and reduced a1uminothermical­ alloy-type scrap is commonly reprocessed ly, and cobalt and nickel sulfides were by secondary metal refiners and down­ leached, solvent-extracted, and e1ectro­ graded in use as nickel-enriched feed­ won individually. Substantial Bureau re­ stock for stainless steel, cast iron, or search was conducted on superal10y recla­ alloy steels. mation in the 1960's using a variety of constant-current e1ectrodeposition and The second largest domestic use of co­ hydrometa1lurgy techniques (i-2). balt is in the production of permanent 3 Underlined numbers in parentheses re­ 4Reference to specific products does fer to items in the list of references at not imply endorsement by the Bureau of the end of this report. Mines. 3 The current investigation involves a idealized and controlled conditions not combined pyrometallurgical and elec­ realized in actual practice for combina­ trometallurgical approach. The Ni-Co­ tions of metals and variations of elec­ bearing material is melted and cast into trolyte ions, pH, etc. Factors such anodes, which are then dissolved in acid as overvoltage, passivity, electrolyte sulfate-chloride electrolyte while the composition, temperature, etc., lead to potential between the cathode and a ref­ shifts in potential and to anomalous erence electrode is controlled to selec­ behavior. tively deposit Ni-Co alloy. Controlled­ potential electrolysis has been used in A main goal of this research is to the past primarily as an analytical tool devise technology for the recovery of and has not been developed for commercial Ni-Co a]loy by electrolysis of anodes selective electrodeposition of metals and cast from superalloy scrap. This ini­ alloys. The controlled potential is re­ tial report describes results obtained lated to the fact that different metals from basic research experiments performed ideally exhibit different reduction po­ on alloy
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