Direct electrochemical reduction of impure metal compounds in molten salts

Abstract

An apparatus and related methods for continuous electrodeposition of metals from impure metal feedstocks are provided. Elemental metals (e.g., Co, Cu) can be deposited from metal feedstocks (e.g., metal compounds such as hydroxides, oxyhydroxides, oxides, or sulfides; ores, including concentrates and mine wastes; tailings; alloys; recycled waste; or scrap metal) in a molten salt electrolyte. An apparatus for continuous electrodeposition comprises: a working electrode comprising a rotary drum having a central axis and a lateral surface, wherein the rotary drum is configured to rotate about the central axis; a counter electrode; and a vessel with an electrolyte bath disposed therein, the electrolyte bath comprising a molten salt electrolyte, wherein the lateral surface of the working electrode is configured to be at least partially submerged in the electrolyte bath. Methods of the present disclosure enable recovery of metals from low concentrations or via processing of ores or dilute waste streams.

What is claimed is: 
     
         1 . An electrodeposition apparatus, comprising:
 a working electrode comprising a rotary drum having a central axis and a lateral surface, wherein the rotary drum is configured to rotate about the central axis;   a counter electrode; and   a vessel with an electrolyte bath disposed therein, the electrolyte bath comprising a molten salt electrolyte,   wherein the lateral surface of the working electrode is configured to be at least partially submerged in the electrolyte bath.   
     
     
         2 . The electrodeposition apparatus of  claim 1 , wherein the counter electrode is substantially concentric with the lateral surface of the working electrode. 
     
     
         3 . The electrodeposition apparatus of  claim 1 , further comprising a scraping member configured to separate electrodeposited metal from the lateral surface of the rotary drum. 
     
     
         4 . The electrodeposition apparatus of  claim 1 , further comprising a fluid flow apparatus configured to transport electrolyte bath into the vessel and/or out of the vessel. 
     
     
         5 . The electrodeposition apparatus of  claim 1 , wherein the electrolyte bath is isolated from ambient atmosphere and is in contact with an inert atmosphere. 
     
     
         6 . The electrodeposition apparatus of  claim 1 , further comprising:
 a potentiostat configured to control a voltage across the working electrode and the counter electrode; and/or   a galvanostat configured to control a current flowing between the working electrode and the counter electrode.   
     
     
         7 . The electrodeposition apparatus of  claim 1 , wherein the molten salt electrolyte comprises one or more of LiOH, NaOH, KOH, and CsOH. 
     
     
         8 . The electrodeposition apparatus of  claim 1 , wherein the molten salt electrolyte comprises one or more molten salt halides, sulfates, carbonates, borates, or nitrates. 
     
     
         9 . The electrodeposition apparatus of  claim 1 , wherein the electrolyte bath further comprises a feedstock comprising a first metal, wherein the first metal is in an average oxidation state of 4+ or less in the feedstock. 
     
     
         10 . A method for electrodeposition of a first metal onto an electrode from a feedstock comprising the first metal, the method comprising:
 providing the feedstock to a molten salt electrolyte, wherein the first metal is in an average oxidation state of 4+ or less in the feedstock;   contacting a working electrode and a counter electrode with the molten salt electrolyte comprising the feedstock; and   applying a voltage across the working electrode and the counter electrode sufficient to electrodeposit the first metal onto the working electrode in elemental form,   wherein:
 the working electrode comprises a rotary drum having a central axis and a lateral surface, wherein the rotary drum rotates about the central axis while the voltage is applied; and 
 at least a portion of the lateral surface is submerged in the molten salt electrolyte while the rotary drum is rotated about the central axis. 
   
     
     
         11 . The method of  claim 10 , wherein electrodeposited metal is removed from a portion of the lateral surface not submerged in the electrolyte bath before the portion is reintroduced into the electrolyte bath. 
     
     
         12 . The method of  claim 10 , wherein the first metal has an average oxidation state of 1+ to 4+ in the feedstock. 
     
     
         13 . The method of  claim 10 , wherein:
 the molten salt electrolyte comprises one or more of LiOH, NaOH, KOH, and CsOH; or   the molten salt electrolyte comprises one or more molten salt sulfates, nitrates, halides, carbonates, or borates.   
     
     
         14 . The method of  claim 10 , wherein the feedstock further comprises a second metal, wherein the second metal has an average oxidation state of 4+ or less in the feedstock. 
     
     
         15 . The method of  claim 14 , wherein after the first metal is electrodeposited onto the working electrode in elemental form, a second voltage is applied across the working electrode and the counter electrode, wherein the second voltage is sufficient to electrodeposit the second metal onto the working electrode in elemental form. 
     
     
         16 . The method of  claim 14 , wherein the voltage applied across the working electrode and the counter electrode is sufficient to co-deposit the first metal and the second metal onto the working electrode in elemental form. 
     
     
         17 . The method of  claim 10 , wherein:
 the feedstock comprises one or more alloys, ores, concentrates, mine wastes, or tailings; or   the feedstock comprises scrap comprising the first metal, and the counter electrode comprises a porous container in contact with the scrap, wherein the first metal is oxidized at the counter electrode via application of an oxidizing voltage before being electrodeposited in elemental form onto the working electrode via application of a reducing voltage.   
     
     
         18 . The method of  claim 10 , wherein:
 the voltage applied across the working electrode and the counter electrode is held constant; or   the voltage applied across the working electrode or the counter electrode is pulsed; or   a current flowing between the working electrode and the counter electrode is held constant; or   the current flowing between the working electrode and the counter electrode is pulsed.   
     
     
         19 . The method of  claim 10 , wherein the molten salt electrolyte is in contact with an inert atmosphere and is isolated from ambient atmosphere. 
     
     
         20 . A method of recycling a metal from a feedstock, the method comprising:
 (a) solubilizing a first metal from the feedstock to obtain a metal composition, wherein the first metal is in an average oxidation state of 4+ or less in the feedstock; and   (b) electrodepositing the first metal in elemental form onto an electrode from the metal composition, the electrodepositing comprising:
 providing the metal composition to a molten salt electrolyte comprising one or more molten salt hydroxides, sulfates, nitrates, halides, carbonates, or borates; 
 contacting a working electrode and a counter electrode with the molten salt electrolyte; and 
 applying a voltage across the working electrode and the counter electrode sufficient to electrodeposit the first metal onto the working electrode in elemental form, 
 wherein:
 the working electrode comprises a rotary drum having a central axis and a lateral surface, wherein the rotary drum is rotated about the central axis; and 
 at least a portion of the lateral surface is submerged in the molten salt electrolyte while rotary drum is rotated about the central axis.