Process for removing oxygen from metal oxides by electrolysis in a fused salt

Abstract

Oxygen is removed from metal or metalloid oxides by electrolysis in a fused salt, to produce elements or alloys, so as to prevent problems of cell contamination and poor power efficiency, particularly in scaled up electro-deoxidation processes. Cell current is controlled not to exceed a selected threshold for substantially all of the electrolysis process. The process may include a first constant current phase and a second constant voltage phase.

1 . A method of extracting a metal, metalloid or alloy from a metal oxide, metalloid oxide or mixture of oxides of alloying elements, by conducting electrolysis in a cell comprising a carbon anode and a fused electrolyte under conditions so as to remove oxygen from the oxide or oxides, wherein the current is controlled so that it does not exceed a selected threshold throughout substantially all of the electrolysis process.  
     
     
         2 . A method according to  claim 1  wherein the metal or alloy comprises titanium.  
     
     
         3 . A method according to  claim 1  wherein the electrolyte comprises calcium chloride.  
     
     
         4 . A method according to  claim 1  wherein more than 0.5 kg of oxide undergoes electro-deoxidation.  
     
     
         5 . A method according to  claim 1  wherein the current threshold is selected such that no substantial visible deposits are formed on the surface of the electrolyte under selected atmospheric conditions.  
     
     
         6 . A method according to  claim 1  wherein the current threshold is selected such that the current density at the anode does not exceed 500 A/m 2 .  
     
     
         7 . A method according to  claim 1  wherein the current is maintained within 20%, and ideally within 10%, of the selected threshold until, even at maximum voltage, the current cannot exceed the threshold.  
     
     
         8 . A method according to  claim 1  wherein the current is prevented from exceeding the selected threshold by use of a control means.  
     
     
         9 . A method according to  claim 8  wherein the control means comprises a current measuring device and a variable voltage supply.  
     
     
         10 . A method according to  claim 1  wherein the atmosphere is maintained at reduced pressure for at least part of the electrolysis process.  
     
     
         11 . A method according to  claim 10  wherein the pressure is below 100 mBar.  
     
     
         12 . A method according to  claim 11  wherein the pressure is in the range 1 to 10 mBar.