Electrochemical cell and process for producing metal and a co-product from metal oxide and an aqueous halide salt

Abstract

An electrochemical cell and process for producing metal and a co-product from metal ore and an aqueous halide salt are described. The co-product may be a metal hydroxide, halogen, oxygen, and/or a hypohalite. The cell includes a cathode, an anode, and a separator. A catholyte includes (i) water, (ii) a metal hydroxide comprising Q, where Q is an alkali metal, an alkaline earth metal, or a combination thereof, and (iii) suspended metal ore particles comprising MxOy where M is a metal and x and y are integers. An anolyte includes (i) water and (ii) a halide salt comprising Q and X where X is Cl or Br. A process for producing metal includes applying a voltage across the electrochemical cell to effect reduction of the MxOy in the cathode compartment to provide the metal M and a hydroxide comprising Q. X2, O2, and/or XO− is formed in the anode compartment.

We claim: 
     
         1 . An electrowinning process , comprising:
 providing an electrochemical cell comprising (i) a cathode comprising low-carbon steel, copper, iron, graphite, vitreous carbon, or titanium, (ii) an anode comprising an oxide coating comprising Ru, Pt, Ir, or any combination thereof, on a conducting substrate, (iii) a separator between the cathode and the anode, the separator comprising a porous composite or a cation-selective membrane, and (iv) a voltage source electrically connected to the cathode and the anode;   providing a catholyte comprising (i) water, (ii) a metal hydroxide comprising Q, where Q is an alkali metal, an alkaline earth metal, or a combination thereof, and (iii) suspended metal ore particles comprising M x O y  where M is a metal and x and y are integers;   providing an anolyte comprising water and a halide salt comprising Q and X, where X is Cl, Br, or a combination thereof; and   applying a voltage across the electrochemical cell to effect (i) reduction of the M x O y  in the catholyte to provide the metal M and additional metal hydroxide comprising Q, and (ii) production of O 2 , X 2 , XO − , or any combination thereof in the anolyte.   
     
     
         2 . The electrowinning process of  claim 1 , wherein:
 the anolyte has a bulk average pH≤3 and X 2  production is greater than O 2  production; or   the anolyte has a bulk average 3<pH<7 and XO −  production is greater than O 2  and/or X 2  production; or   the anolyte has a bulk average pH≥7 and O 2  production is greater than X 2  production.   
     
     
         3 . The electrowinning process of  claim 2 , wherein:
 the anolyte has a pH≤3 and the anode is in direct contact with the separator; or   the anolyte has a pH≥7 and the anode is spaced apart from the separator.   
     
     
         4 . The electrowinning process of  claim 1 , applying the voltage across the electrochemical cell further effects production of H 2  in the catholyte. 
     
     
         5 . The electrowinning process of  claim 1 , wherein:
 (i) M is Fe, Mn, Ni, Cr, Co, Zn, or any combination thereof; or   (ii) Q is Li, Na, K, Rb, Cs, Mg, Ca, or any combination thereof; or   (iii) both (i) and (ii).   
     
     
         6 . The electrowinning process of  claim 1 , wherein:
 (i) the metal ore particles comprise Fe 2 O 3 ; or   (ii) Q is Na;   (iii) X is Cl; or   (iv) any combination of two or more of (i), (ii), and (iii).   
     
     
         7 . The electrowinning process of  claim 1 , wherein:
 (i) the catholyte comprises from 50 g/L to 500 g/L of the suspended metal ore particles prior to applying the voltage; or   (ii) the catholyte comprises from 10 wt % to 50 wt % of the metal hydroxide prior to applying the voltage; or   (iii) the anolyte comprises from 10 wt % to 50 wt % of the halide salt prior to applying the voltage; or   (iv) any combination of two or more of (i), (ii), and (iii).   
     
     
         8 . The electrowinning process of  claim 1 , further comprising:
 (i) continuously or periodically removing X 2  and/or O 2  generated in the anolyte; or   (ii) periodically removing at least a portion of the metal M from the cathode; or   (iii) continuously or periodically removing H 2  generated in the catholyte; or   (iv) any combination of two or more of (i), (ii), and (iii).   
     
     
         9 . The electrowinning process of  claim 1 , further comprising:
 (i) periodically adding a quantity of the metal ore particles to the catholyte; or   (ii) periodically adding a quantity of the halide salt to the anolyte; or   (iii) both (i) and (ii).   
     
     
         10 . The electrowinning process of  claim 1 , wherein the metal ore particles are obtained from a metal ore feedstock further comprising aluminates, silicates, or aluminates and silicates, the method further comprising leaching at least a portion of the aluminates, silicates, or aluminates and silicates from the metal ore feedstock by contacting the metal ore feedstock with a hydroxide solution to provide the metal ore particles. 
     
     
         11 . The electrowinning process of  claim 10 , wherein the hydroxide solution is a spent catholyte obtained from the electrochemical cell after applying the voltage across the electrochemical cell. 
     
     
         12 . The electrowinning process of  claim 1 , wherein the anolyte comprises concentrated seawater having a halide salt concentration of from 10 wt % to 50 wt %. 
     
     
         13 . The electrowinning process of  claim 1 , wherein:
 providing the electrochemical cell further comprises providing a cell stack comprising
 (i) a number of the electrochemical cells, a cathode electrical connector connecting cathodes of each of the electrochemical cells in parallel, an anode electrical connector connecting anodes of each of the electrochemical cells in parallel, and a voltage source electrically connected to the cathode electrical connector and the anode electrical connector, or 
 (ii) a number n of the electrochemical cells, a number n−1 of conductive bipolar plates wherein a conductive bipolar plate is positioned between each adjacent pair of electrochemical cells, a cathode electrical connector connected to a cathode of a first electrochemical cell in the series, an anode electrical connector connected to an anode of a last electrochemical cell in the series, and a voltage source electrically connected to the cathode electrical connector and the anode electrical connector; 
   providing the catholyte further comprises providing the catholyte within each electrochemical cell of the cell stack;   providing the anolyte within the anode compartment further comprises providing the anolyte within each electrochemical cell of the cell stack; and   applying a voltage across the electrochemical cell further comprises applying the voltage across the cell stack to effect reduction of the M x O y  in each cathode compartment to provide the metal M and formation of Cl 2  gas in each anode compartment.   
     
     
         14 . The electrowinning process of  claim 1 , wherein:
 (i) the voltage applied is from 2 V to 5 V per electrochemical cell; or   (ii) the electrochemical cell or cell stack is operated at a current density of from 20 mA cm −2  to 500 mA cm −2 ; or   (iii) the electrochemical cell or cell stack is operated at a temperature from 25° C. to 150° C.; or   (iv) any combination of (i), (ii), and (iii).   
     
     
         15 . An electrochemical cell, comprising:
 a cathode comprising low-carbon steel, copper, iron, graphite, vitreous carbon, or titanium;   an anode comprising an oxide coating comprising Ru, Pt, Ir, or any combination thereof, on a conducting substrate; and   a separator between the cathode and the anode, the separator comprising a cation-selective membrane that is permeable to alkali metal cations, alkaline earth metal cations, or a combination thereof.   
     
     
         16 . The electrochemical cell of  claim 15 , further comprising:
 a second anode; and   a second separator between the cathode and the second anode, the second separator comprising a cation-selective membrane that is permeable to alkali metal cations, alkaline earth metal cations, or a combination thereof.   
     
     
         17 . The electrochemical cell of  claim 15 , further comprising:
 (i) gas collecting means for collecting gas generated at the anode; or   (ii) gas collecting means for collecting gas generated at the cathode; or   (iii) a magnet operable to be passed over a surface of the cathode; or   (iv) a catholyte mixing means and an anolyte mixing means; or   (v) a voltage source electrically connected to the cathode and the anode; or   (vi) any combination of two or more of (i), (ii), (iii), (iv), and (v).   
     
     
         18 . The electrochemical cell of  claim 15 , further comprising:
 a catholyte comprising (i) water, (ii) a metal hydroxide comprising Q, where Q is an alkali metal, an alkaline earth metal, or a combination thereof, and (iii) suspended metal ore particles comprising M x O y  where M is a metal and x and y are integers; and   an anolyte comprising water and a halide salt comprising Q and X where X is Cl or Br.   
     
     
         19 . A cell stack, comprising:
 (a) a number n of electrochemical cells according to  claim 15 ,
 a cathode electrical connector connecting cathodes of each of the electrochemical cells in parallel, and 
 an anode electrical connector connecting anodes of each of the electrochemical cells in parallel; or 
   (b) a number n of electrochemical cells according to  claim 13  arranged in series,
 a number n−1 of conductive bipolar plates, a conductive bipolar plate positioned between each adjacent pair of electrochemical cells, 
 a cathode electrical connector connected to a cathode of a first electrochemical cell in the series, and 
 an anode electrical connector connected to an anode of a last electrochemical cell in the series. 
   
     
     
         20 . The cell stack of  claim 19 , further comprising:
 a catholyte within each electrochemical cell, the catholyte comprising (i) water, (ii) a metal hydroxide comprising Q, where Q is an alkali metal, an alkaline earth metal, or a combination thereof, and (iii) suspended metal ore particles comprising M x O y  where M is a metal and x and y are integers; and   an anolyte within each electrochemical cell, the anolyte comprising water and a halide salt comprising Q and X where X is Cl or Br.