Electrowinning cell and process

Abstract

An electrochemical cell and method for electrowinning a variety of multivalent metals including titanium is described. In one aspect, the invention provides an electrochemical cell comprising an anolyte chamber comprising an anode and configured for containing an anolyte, a catholyte chamber comprising a cathode and configured for containing a catholyte comprising a metal to be electrolytically produced, and a diaphragm separating the anolyte chamber and the catholyte chamber, the diaphragm configured to control the potential drop across the diaphragm so that it is below the potential difference required for inducing bipolarity at the diaphragm.

What is claimed is: 
     
         1 . An electrochemical cell comprising:
 an anolyte chamber comprising an anode and configured for containing an anolyte;   a catholyte chamber comprising a cathode and configured for containing a catholyte comprising a metal to be electrolytically produced; and   a diaphragm separating the anolyte chamber and the catholyte chamber, the diaphragm configured to control the potential drop across the diaphragm so that it is below the potential difference for the onset of bipolarity at the diaphragm.   
     
     
         2 . The electrochemical cell of  claim 1 , wherein the diaphragm has a thickness lower than a thickness that allows bipolar reactions. 
     
     
         3 . The electrochemical cell of  claim 2 , wherein the diaphragm comprises a plurality of diaphragms. 
     
     
         4 . The electrochemical cell of  claim 3 , comprising a space between successive diaphragms of the plurality of diaphragms. 
     
     
         5 . The electrochemical cell of  claim 3 , wherein the space between successive diaphragms comprises an open space to be filled by electrolyte or comprises a porous insulating spacer disposed in the space. 
     
     
         6 . The electrochemical cell of  claim 3 , wherein each diaphragm has a different thickness. 
     
     
         7 . The electrochemical cell of  claim 2 , wherein the metal to be electrolytically produced is titanium. 
     
     
         8 . The electrochemical cell of  claim 2 , wherein the diaphragm has a thickness of about 0.8 cm or less. 
     
     
         9 . The electrochemical cell of  claim 2 , wherein the diaphragm comprises a plurality of diaphragms, and each diaphragm in the plurality of diaphragms has a thickness of about 0.8 cm or less. 
     
     
         10 . The electrochemical cell of  claim 9 , comprising a space disposed between successive diaphragms. 
     
     
         11 . The electrochemical cell of  claim 1 , wherein the diaphragm has a porosity that is larger than a porosity that allows for the onset of bipoloar reactions for a given thickness, electrolyte conductivity, and current density. 
     
     
         12 . The electrochemical cell of  claim 11 , wherein the diaphragm comprises a plurality of diaphragms, and each diaphragm has a porosity that is larger than a porosity that allows for the onset of bipoloar reactions for a given thickness, electrolyte conductivity, and current density. 
     
     
         13 . The electrochemical cell of  claim 12 , wherein each diaphragm has a different porosity. 
     
     
         14 . An electrowinning process for deposition of a metal from a solution comprising:
 (a) providing an electrochemical cell comprising:
 an anolyte chamber comprising an anode and an anolyte solution dispersed in the anolyte chamber; 
 a catholyte chamber comprising a cathode and an cathode solution dispersed in the cathode chamber, the catholyte solution comprising a fluid containing at least one metal dissolved therein; and 
 a diaphragm separating the anolyte chamber and the catholyte chamber; and 
   (b) establishing a predetermined voltage and current across the electrolytic cell sufficient to effect reduction and deposition of the at least one metal at the cathode and cause an oxidation reaction at the anode, wherein the diaphragm is configured to control the potential drop across the diaphragm so that it is below the onset potential for bipolarity.   
     
     
         15 . The electrowinning process of  claim 14 , wherein the diaphragm has a thickness lower than a thickness that allows for the onset of bipolar reactions. 
     
     
         16 . The electrowinning process of  claim 14 , wherein the diaphragm comprises a plurality of diaphragms. 
     
     
         17 . The electrowinning process of  claim 16 , comprising a space separating successive diaphragms in the plurality of diaphragms. 
     
     
         18 . The electrowinning process of  claim 16 , wherein the diaphragms each have a thickness lower than a thickness that allows for the onset of bipolar reactions. 
     
     
         19 . The electrowinning process of  claim 14 , wherein a constant or time-varying current or potential is applied to the diaphragm. 
     
     
         20 . The electrowinning process of  claim 14 , comprising depositing titanium, chromium, iron, uranium, a trans-uranium metal, or a combination of two or more thereof at the cathode. 
     
     
         21 . The electrowinning process of  claim 14 , wherein the catholyte and anolyte comprise aqueous or non-aqueous solutions. 
     
     
         22 . The electrowinning process of  claim 14 , wherein the diaphragm has a porosity that is larger than a porosity that allows for the onset of bipolar reactions for a given thickness, electrolyte conductivity, and current density.