Process and system for treating the discharge stream from an ion exchanger

Abstract

A method is disclosed for treating a flushing solution from an ion exchanger used in electroplating operations by co-precipitating or selectively precipitating out metal hydroxides derived from metal ions from the structures being plated in the electroplating bath, metal ions from the electrodes use in the electroplating bath and metal ions from the plating metal used in the electroplating bath, and a pH raising agent having a cation with a valence of at least 2. After the metals are precipitated out of the flushing solution, the flushing solution is aerated with carbon dioxide to precipitate out the cation from the pH raising agent as a carbonate. The carbonate precipitate is removed from the flushing solution and the resulting solution consists essentially of water that may be recycled for use in the electroplating plant or safely discharged into the environment.

What is claimed is:  
     
         1 . A method for treating an aqueous solution discharged from an ion exchanger during a flushing thereof wherein an acidic aqueous flushing solution is caused to flow through said exchanger to increase a hydrogen ion content of said exchanger and wherein the resulting aqueous discharge solution is acidic and comprises metal ions from structures being electroplated in an electroplating bath, metal ions from electrodes used in the electroplating bath, and metal ions from the plating metal in said electroplating bath, said method comprising: 
 adding a pH raising agent having a cation with a valence of at least 2 to said discharge solution to raise the solution's pH such that hydroxyl ions in the discharge solution (i) bond with the metal ions from the structures being plated in said electroplating bath to form a first precipitate; (ii) bond with the metal ions from said electrodes to form a second precipitate; and (iii) bond with the metal ions from the plating metal to form a third precipitate;    affecting separation of said first, second and third precipitates from said discharge solution;    aerating the discharge solution with carbon dioxide, such that said cation from said pH raising agent reacts with said carbon dioxide to form a carbonate precipitate; and    separating said carbonate precipitate from said solution such that the solution consists essentially of water.    
     
     
         2 . A method according to  claim 1  further comprising adding a flocculating agent to said discharge solution prior to separating the first, second and third precipitates from the discharge solution.  
     
     
         3 . A method according to  claim 1  wherein the pH raising agent comprises a material selected from the group consisting of calcium hydroxide, calcium oxide, calcium magnesium hydroxide, calcium magnesium oxide, barium hydroxide and barium oxide.  
     
     
         4 . A method according to  claim 1  wherein the pH raising agent is calcium carbonate.  
     
     
         5 . A method according to  claim 4  wherein the aqueous flushing solution comprises sulfuric acid and the resulting aqueous discharge solution further comprises sulfuric acid, wherein said calcium carbonate reacts with the sulfuric acid in said discharge solution to form calcium sulfate that precipitates from said discharge solution, water that remains in said discharge solution, and carbon dioxide that aerates from said discharge solution, and wherein said separation of the first, second and third precipitates further comprises separating said calcium sulfate from said discharge solution along with said first, second and third precipitates.  
     
     
         6 . A method according to  claim 1  further comprising recovering the third precipitate for reuse in the electroplating bath.  
     
     
         7 . A method according to  claim 1  further comprising, after separating said carbonate precipitate, recycling said water for internal use within an electroplating plant.  
     
     
         8 . A method according to  claim 1  further comprising recovering the separated carbonate precipitate for reuse in said method.  
     
     
         9 . A method for treating an aqueous solution discharged from an ion exchanger during a flushing thereof wherein an acidic aqueous flushing solution is caused to flow through said exchanger to increase a hydrogen ion content of said exchanger and wherein the resulting aqueous discharge solution is acidic and comprises metal ions from structures being electroplated in an electroplating bath, metal ions from electrodes used in the electroplating bath, and chromium (VI) ions from the plating metal in said electroplating bath, said method comprising: 
 adding a reducing agent to the discharge solution to reduce the chromium (VI) ions to chromium (III) ions;    adding pH raising agent having a cation with a valence of at least 2 to said discharge solution to raise the solution's pH such that hydroxyl ions in the discharge solution (i) bond with the metal ions from the structures being plated in said electroplating bath to form a first precipitate; (ii) bond with the metal ions from said electrodes to form a second precipitate; and (iii) bond with the chromium (III) ions to form a third precipitate of chromium (III) hydroxide; and    affecting separation of said first, second and third precipitates from said discharge solution;    aerating the discharge solution with carbon dioxide, such that said cation from said pH raising agent reacts with said carbon dioxide to form a precipitate and water; and    separating said precipitate from said discharge solution such that the discharge solution consists essentially of water.    
     
     
         10 . A method according to  claim 9  further comprising adding a flocculating agent to said discharge solution.  
     
     
         11 . A method according to  claim 9  wherein the pH raising agent comprises a material selected from the group consisting of calcium hydroxide, calcium oxide, calcium magnesium hydroxide, calcium magnesium oxide, barium hydroxide and barium oxide.  
     
     
         12 . A method according to  claim 9 , wherein the pH raising agent is calcium carbonate.  
     
     
         13 . A method according to  claim 9 , wherein the pH raising agent raises the pH between 7 and 9.  
     
     
         14 . A method according to  claim 9 , wherein the pH raising agent raises the pH to about 8.3.  
     
     
         15 . A method according to  claim 12  wherein the flushing solution is sulfuric acid and said sulfuric reacts with the calcium carbonate to form a calcium sulfate precipitate that is separated from the discharge solution with the first, second and third precipitates.  
     
     
         16 . A method according to  claim 9 , wherein said reducing agent is elemental iron.  
     
     
         17 . A method according to  claim 16 , wherein said elemental iron is derived from discarded steel shavings and wherein the iron ions from the elemental iron bond with the hydroxyl ions to further form said first precipitate.  
     
     
         18 . A method according to  claim 9 , wherein the metal ions from the structures plated in said bath are iron (III) ions and wherein the metal ions from the electrodes used in said bath are copper (II) ions.  
     
     
         19 . A method according to  claim 9  further comprising, after separating said precipitate from said discharge solution such that the discharge solution consists essentially of water, recycling said water for internal use within an electroplating plant.  
     
     
         20 . A method according to  claim 19  further comprising recovering the separated said precipitate for reuse in said method.