Method for exfoliating coating layer of electrode for electrolysis

Abstract

The present invention relates to a method for effectively exfoliating a coating layer from the surface of the conductive substrate of a used electrode for electrolysis comprising an insoluble metal electrode having the coating layer containing electrode substance comprising noble metals and/or their metal oxides on the surface of the used electrode substrate comprising valve metals, such as titanium and tantalum or valve metal alloys, and then to recover the electrode substances and/or electrode substrate for recycling use. The method for exfoliating comprises the steps of treating the insoluble metal electrode surface having the coating layer, in succession, with an alkali treatment process using a caustic alkali aqueous solution, a heating and a baking process and an acid treatment process, the alkali treatment process being conducted by applying an alkali treatment solution prepared by adding thickener to the caustic alkali aqueous solution.

1 . A method for exfoliating a coating layer from a surface of an electrode substrate for electrolysis, the coating layer containing electrode substance comprising noble metal and/or metal oxide thereof on the surface of the electrode substrate, the electrode substrate comprising valve metals including titanium and tantalum or valve metal alloys, the method comprising:
 treating the surface of the electrode substrate having the coating layer containing the electrode substance comprising noble metal and/or metal oxide thereof on the surface of the electrode substrate, in succession, with an alkali treatment process using a caustic alkali aqueous solution;   heating and baking; and   treating with an acid treatment process,   
       wherein the alkali treatment process is conducted by applying an alkali treatment solution prepared by adding thickener to the caustic alkali aqueous solution. 
     
     
         2 . The method for exfoliating the coating layer from the surface of the electrode substrate as in  claim 1 , wherein the thickener comprising natural polysaccharide thickener is applied. 
     
     
         3 . The method for exfoliating the coating layer from the surface of the electrode substrate as in  claim 2 , wherein the thickener comprising bio gum or guar gum derivatives or cellulose derivatives are applied as the natural polysaccharide thickener. 
     
     
         4 . The method for exfoliating the coating layer from the surface of the electrode substrate as in  claim 1 , wherein the thickener comprising carboxymethil cellulose is applied as thickener. 
     
     
         5 . The method for exfoliating the coating layer from the surface of the electrode substrate as in  claim 1 , wherein the thickener comprising xanthan gum is applied as thickener. 
     
     
         6 . The method for exfoliating the coating layer from the surface of the electrode substrate as  claim 1 , wherein the addition ratio of the thickener in the alkali treatment solution is 0.2 mass % or more but 1 mass % or less. 
     
     
         7 . The method for exfoliating the coating layer from the surface of the electrode substrate as in  claim 1 , wherein the addition ratio of the thickener in the alkali treatment solution is 0.4 mass % or more but 1 mass % or less.