Process for the preparation of zinc dithionite

Abstract

Disclosed is a process for preparing zinc dithionite comprising reacting zinc metal with sulfur dioxide, wherein the zinc metal used in the reaction is produced by electrochemical reduction in an undivided electrochemical cell of an aqueous alkaline slurry or solution of zinc oxide or any other zinc compound that reacts with aqueous base to form zinc oxide.

What is claimed is:  
     
         1 . A process for preparing zinc dithionite comprising reacting zinc metal with sulfur dioxide, wherein the zinc metal used in the reaction is produced by electrochemical reduction in an undivided electrochemical cell of an aqueous alkaline slurry or solution of zinc oxide or any other zinc compound that reacts with aqueous base to form zinc oxide.  
     
     
         2 . 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+ .  
     
     
         3 . The process of  claim 1 , that is substantially free of labor-intensive steps comprising removal of cathode after completion of the electrochemical reduction of the zinc oxide.  
     
     
         4 . The process of  claim 1 , that is substantially free of labor-intensive steps comprising clarifying a slurry of zinc oxide in an aqueous basic solution by sedimentation and filtration prior to the electrochemical reduction of the zinc oxide.  
     
     
         5 . The process of  claim 1 , that is substantially free of labor-intensive steps comprising drying, grinding, and sizing of zinc metal particles prior to the reaction of the zinc metal with sulfur dioxide.  
     
     
         6 . The process of  claim 1 , wherein the zinc metal used for reaction with sulfur dioxide is in the form of wet zinc metal particles.  
     
     
         7 . The process of  claim 1 , wherein the current efficiency for the production of zinc dithionite is at least 70%, 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.  
     
     
         8 . The process of  claim 7 , wherein the current efficiency for the production of zinc dithionite is at least 75%.  
     
     
         9 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes a magnesium or copper cathode.  
     
     
         10 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes a stainless steel or nickel anode.  
     
     
         11 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes a magnesium cathode and a stainless steel anode.  
     
     
         12 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes a magnesium cathode and a nickel anode.  
     
     
         13 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes a copper cathode and a nickel anode.  
     
     
         14 . The process of  claim 1 , wherein the undivided electrochemical cell utilizes a copper cathode and a stainless steel anode.  
     
     
         15 . The process of  claim 1 , wherein the electrochemical reduction is carried out at a temperature range of about 100 to about 105° C.  
     
     
         16 . The process of  claim 14 , wherein the aqueous base comprises ions of at least one alkali or alkaline earth metal and hydroxyl (OH − ) ions.  
     
     
         17 . The process of  claim 15 , 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.  
     
     
         18 . The process of  claim 15 , wherein the compound is selected from the group consisting of sodium hydroxide and potassium hydroxide.  
     
     
         19 . The process of  claim 1 , wherein the electrochemical reduction is carried out at a current density of about 500 to about 30,000 Amps/m 2 .  
     
     
         20 . The process of  claim 1 , wherein the reaction of the zinc metal produced electrochemically in an undivided cell with sulfur dioxide is carried out at a temperature of about 20 to about 60° C.  
     
     
         21 . The process of  claim 1 , wherein the reaction of zinc metal with sulfur dioxide to produce zinc dithionite is conducted in the presence of cadmium sulfate.  
     
     
         22 . The process of  claim 1 , wherein the reaction of zinc metal with sulfur dioxide to produce zinc dithionite is conducted in the substantial absence of cadmium sulfate.