Cobalt extraction: Difference between revisions
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[[File:Cobalt OreUSGOV.jpg|thumb|right|upright|Cobalt ore]] |
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Several methods exist for the separation of [[cobalt]] from [[copper]] and [[nickel]]. They depend on the concentration of cobalt and the exact composition of the used [[ore]]. |
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The Sherritt process is a [[hydrometallurgy|hydrometallurgical]] process named for Sherritt Gordon Mines Ltd. (now [[Sherritt International]]) of [[Sherridon, Manitoba|Sherridon]] and [[Lynn Lake]] [[Manitoba]] [[Canada]], based on the older Forward process developed by Dr. [[Frank Forward]] for the recovery of copper and nickel from those same mines. Nickel sulfide concentrates can be treated by either roasting or flash smelting to produce [[Matte (metallurgy)|matte]] from which nickel and cobalt can be recovered hydrometallurgically, or they may be treated by an [[ammonia]] solution pressure leach. The residue is removed. A feed of matte and sulfide concentrate containing approximately 0.4% cobalt and 30% sulfur is pressure leached at elevated temperature and pressure in an ammoniacal solution to produce a solution of nickel, copper and cobalt. By boiling away the ammonia; copper is precipitated as a sulfide and sent to a smelter. Hydrogen sulfide is added to the [[autoclave]] to remove nickel sulfide and [[copper sulfide]] which is fed back to the leaching process. Air is then passed through the solution in the autoclave for [[Hydrolysis#Hydrolysis of metal aqua ions|oxyhydrolysis]]. The solution is then [[Redox|reduced]] with hydrogen, again at high temperature and pressure, to precipitate nickel powder (>99%). The remaining solution (containing approximately equal proportions of nickel and cobalt sulfides), is then adjusted (to a lower temperature and pressure) to precipitate the mixed sulfides and the fluid is concentrated and crystallized into [[ammonium sulfate]] ((NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>). The mixed sulfides are pressure leached with air and sulfuric acid. Ammonia is then added to remove [[potassium]] and iron as [[jarosite]] (KFe<sup>3+</sup><sub>3</sub> (OH)<sub>6</sub>(SO<sub>4</sub>)<sub>2</sub>). More ammonia and air is added for [[oxidation]]. The solution is removed from the autoclave and sulfuric acid added to remove nickel as [[nickel(II) sulfate]]-[[ammonium sulfate]] [[hexahydrate]] ((NiSO<sub>4</sub>)•((NH<sub>4</sub>)<sub>2</sub>SO<sub>4</sub>)•6H<sub>2</sub>O) which is then sent to have its nickel recovered. The solution is then further reduced with more sulfuric acid and cobalt metal powder is added to aid in the nucleation of precipitants ([[Seed crystal|seeding]]). Addition of hydrogen gas to saturation precipitates cobalt powder with a [[Fineness|purity]] of approximately 99.6%. |
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==Recovery from copper-cobalt oxide concentrates== |
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The ore is [[Comminution|comminuted]] and the cobalt rich oxides are separated by [[froth flotation]]. The cobalt-bearing concentrate is then mixed with lime and [[coal]], and then [[Smelting|melted]] in a [[reducing atmosphere]]. Iron and lighter impurities float to the surface as solid [[dross]] or are expelled from the melt as gas. The remaining liquid is composed of a heavier copper smelt containing approximately 5% cobalt that is processed for its copper and a lighter [[slag]] that is approximately 40% cobalt that is further refined by hydrometallurgical and electrolytic processing. Concentrations of [[Cobalt(II,III) oxide|cobalt oxide]] (Co<sub>3</sub>O<sub>4</sub>) may also be reduced by the [[aluminothermic]] reaction or with carbon in a [[blast furnace]].<ref>Holleman, A. F., Wiberg, E., Wiberg, N. (2007). "Cobalt" (in German). Lehrbuch der Anorganischen Chemie, 102nd ed.. de Gruyter. pp. 1146–1152. ISBN 978-3-11-017770-1.</ref> |
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==Recovery from laterite ores== |
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Nickel-cobalt [[laterite|laterit]]ic ores can be treated by either hydrometallurgical processes or [[pyrometallurgical]] processes, such as matte or [[ferronickel]] smelting, which require the entire ore to be melted and the metal values to be separated from the residual components of the ore. The hydrometallurgical process for laterite ore can use sulfuric acid or ammonia leach solutions.<ref>{{cite book|page = 346| title = ASM specialty handbook: nickel, cobalt, and their alloys| author =Joseph R. Davis| publisher = ASM International| year = 2000| isbn = 0-87170-685-7| url = http://books.google.com/books?id=IePhmnbmRWkC&dq=cobalt+copper+nickel+ore+separate&num=100}}</ref> |
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==Recovery from arsenide ores== |
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[[Arsenic]] containing concentrates are roasted in a fluidized bed to remove 60% to 70% of the arsenic present as [[arsenic oxide]] (As<sub>2</sub>O<sub>5</sub>). The roasted ores can be treated with [[hydrochloric acid]] and [[chlorine]] or with [[sulfuric acid]] to give a leach solution that can be purified by hydrometallurgical methods and from which cobalt can be recovered by electro refining or by [[carbonate]] precipitation.<ref>{{cite book|page = 347| title = ASM specialty handbook: nickel, cobalt, and their alloys| author =Joseph R. Davis| publisher = ASM International| year = 2000| isbn = 0-87170-685-7| url = http://books.google.com/books?id=IePhmnbmRWkC&dq=cobalt+copper+nickel+ore+separate&num=100}}</ref> If hydrochloric acid is used then cobalt may be extracted using alamine 336 in ''[[meta]]''-[[xylene]].<ref>M. Filiz, N.A. Sayar and A.A. Sayar, ''Hydrometallurgy'', 2006, '''81''', 167-173.</ref> Cobalt can be extracted also using Cyanex 272 {''bis''-(2,4,4-trimethylpentyl) phosphinic acid}. When [[Cobalt carbonate]] (CoCO<sub>3</sub>) is heated (calcined) above 400 °C it decomposes into [[carbon dioxide]] (CO<sub>2</sub>) and [[Cobalt(II) oxide]] (CoO) and can be refined as an oxide concentrate (see above). |
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==Electro refining== |
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If purifying by electrolysis, an aqueous sulfate solution at 50° to 70°C is usually used with a [[lead]] anode (corrosion products from which will not contaminate the cobalt oxy-hydroxide (CoOOH) electrolyte solution) and a [[stainless steel]] cathode which will allow for the easy removal of the deposited cobalt.<ref>R.R. Moskalyk, A.M. Alfantazi, Review of Present Cobalt Recovery Practice, Minerals & Metallurgical Processing, vol 17, 4, 2000, pp. 205-216.</ref> Electro refining in a chloride or sulfate medium at -0.3 V will make a cathode coating of 99.98% Cobalt. |
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==See also== |
==See also== |
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