Electrochemical process for preparing zinc metal and process for preparing zinc dithionite using electrochemically produced zinc metal

Abstract

The present invention provides a low corrosion electrochemical process for preparing zinc metal which comprises electrochemically reducing an aqueous alkaline slurry or solution of zinc oxide or any other compound that reacts with an aqueous base to produce zinc oxide, wherein the electrochemical process is carried out in an undivided electrochemical cell and wherein sodium bisulfide (NaSH) is added to the aqueous alkaline slurry or solution. The present invention also provides a process for preparing zinc dithionite, which comprises reacting zinc metal with sulfur dioxide, wherein the zinc metal is produced by the aforementioned electrochemical process.

What is claimed is:  
     
         1 . A low corrosion electrochemical process for preparing zinc metal which comprises electrochemically reducing an aqueous alkaline slurry or solution of zinc oxide or any other compound that reacts with an aqueous base (alkali) to produce zinc oxide, wherein the electrochemical process is carried out in an undivided electrochemical cell and wherein sodium bisulfide (NaSH) is added to the aqueous alkaline slurry or solution.  
     
     
         2 . The process of  claim 1 , wherein the sodium bisulfide is added prior to beginning the electrochemical reduction.  
     
     
         3 . The process of  claim 1 , wherein the aqueous alkaline slurry or solution of zinc oxide or any other zinc compound that reacts with the aqueous base to form zinc oxide, comprises solubilized zinc based species, said species comprising at least one member selected from the group consisting of ZnO 2   2− , HZnO 2   1− , Zn(OH) + , Zn(OH) 2 , and Zn 2+ .  
     
     
         4 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes copper or stainless steel cathodes.  
     
     
         5 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes a copper cathode and a nickel anode.  
     
     
         6 . The process of claim  1 a, wherein the undivided electrochemical cell utilizes a copper cathode and a stainless steel anode.  
     
     
         7 . The process of  claim 1 , wherein the aqueous base comprises ions of at least one alkali or alkaline earth metal and hydroxyl (OH − ) ions.  
     
     
         8 . The process of  claim 7 , wherein the alkali and alkaline earth metal ions are selected from sodium, potassium, and mixtures thereof and are provided in the form of a compound selected from hydroxides, and oxides.  
     
     
         9 . The process of claim  1 a, wherein the electrochemical reduction is carried out at a temperature range of about 100 to about 85° C.  
     
     
         10 . The process of  claim 1 , wherein the electrochemical reduction is carried out at a temperature range of about 20° to about 70° C.  
     
     
         11 . The process of  claim 1 , wherein the electrochemical reduction is carried out at a current density of about 500 to about 20,000 Amps/m 2 .  
     
     
         12 . The process of  claim 1 , wherein the concentration of sodium bisulfide is at least 0.005 g/100 g of electrolyte.  
     
     
         13 . The process of  claim 1 , wherein the concentration of sodium bisulfide ranges from about 0.01 g/100 g of electrolyte to about 0.01 g/100 g electorolyte.  
     
     
         14 . A process for preparing zinc dithionite which comprises reacting zinc metal with sulfur dioxide, wherein the zinc metal is produced by the electrochemical process of  claim 1 .  
     
     
         15 . The process of  claim 14 , wherein the zinc metal used for the reaction with sulfur dioxide is in the form of wet zinc metal particles.  
     
     
         16 . The process of  claim 14 , wherein the current efficiency for the production of zinc dithionite is at least 75%, the current efficiency for said production being obtained by multiplying the current efficiency for zinc metal formation with the conversion efficiency of zinc metal to zinc dithionite.  
     
     
         17 . The process of  claim 16 , wherein the current efficiency for the production of zinc dithionite is at least 80%.  
     
     
         18 . The process of  claim 14 , wherein the reaction of zinc metal with sulfur dioxide is carried out at a temperature of about 20 to about 60° C.  
     
     
         19 . The process of  claim 14 , wherein the reaction of zinc metal with sulfur dioxide is conducted in the presence of cadmium sulfate.  
     
     
         20 . The process of  claim 14 , wherein the reaction of zinc metal with sulfur dioxide to produce zinc dithionite is conducted in the substantial absence of cadmium sulfate.