Process for the regeneration of exhausted chromium-plating solutions by two-stage diaphragm electrolysis

Claim 2

A process for treating an exhausted iron-containing chromium-plating solution by two-stage diaphragm electrolysis to remove iron values contained in said exhausted chromium-plating solution and regenerate the solution, comprising the steps of conducting a first electrolysis with an accompanying electrodialysis of chromic acid values in a diaphragm electrolytic cell partitioned by a diphragm into an anode compartment containing a diluted aqueous chromic acid solution and a cathode compartment containing an exhausted chromium-plating solution; interrupting said first electrolysis when the chromic acid concentration in the anode compartment reaches a predetermined level due to the transfer and extraction of the chromic acid values in the cathode compartment into the anode compartment by the electrodialysis while iron values precipitate in the cathode compartment; withdrawing for use as a chromium-plating bath the solution obtained in the anode compartment; transferring the obtained solution in said cathode compartment into said anode compartment; charging said cathode compartment with an exhausted chromium plating solution; and conducting a second electrolysis to effect the electrolytic oxidation in said anode compartment and to effect the electrodialysis of the chromic acid values in said cathode compartment to transfer and extract the chromic acid values into said anode compartment while the iron values precipitate in the cathode compartment as the hydroxide, thereby increasing the chromic acid concentration in said anode compartment to a predetermined level.

Claim 3

A process for treating an exhausted iron-containing chromium-plating solution by two-stage diaphragm electrolysis to remove iron values contained in said exhausted chromium-plating solution and regenerate the solution, comprising the steps of conducting a first electrolysis with an accompanying electrodialysis of chromic acid values in a diaphragm electrolytic cell partitioned by a diaphragm into an anode compartment containing a diluted aqueous solution of exhausted chromium-plating solution obtained by diluting the exhausted-plating solution with water and a cathode compartment containing an exhausted chromium-plating solution; interrupting said first electrolysis when the chromic acid concentration in the anode compartment reaches a predetermined level due to the transfer and extraction of the chromic acid values in the cathode compartment into the anode compartment by the electrodialysis while iron values precipitate in the cathode compartment; withdrawing for use as a chromium-plating bath the solution obtained in the anode compartment; transferring the obtained solution in said cathode compartment into said anode compartment; charging said cathode compartment with an exhausted chromium plating solution; and conducting a second electrolysis to effect the electrolytic oxidation in said anode compartment and to effect the electrodialysis of the chromic acid values in said cathode compartment to transfer and extract the chromic acid values into said anode compartment while the iron values precipitate in the cathode compartment as the hydroxide, thereby increasing the chromic acid concentration in said anode compartment to a predetermined level.

Claim 4

A process for treating an exhausted iron-containing chromium-plating solution by two-stage diaphragm electrolysis to remove iron values contained in said exhausted chromium-plating solution and regenerate the solution, comprising the steps of conducting a first electrolysis with an accompanying electrodialysis of chromic acid values in a diaphragm electrolytic cell partitioned by a diaphragm into an anode compartment containing a diluted aqueous solution of exhausted chromium-plating solution obtained by diluting the exhausted-plating solution with water and a cathode compartment containing an exhausted chromium-plating solution; interrupting said first electrolysis when the chromic acid concentration in the anode compartment reaches a predetermined level due to the transfer and extraction of the chromic acid values in the cathode compartment into the anode compartment by the electrodialysis while iron values precipitate in the cathode compartment; withdrawing for use as a chromium-plating bath the solution obtained in the anode compartment; transferring the obtained solution in said cathode compartment into said anode compartment; charging said cathode compartment with an exhausted chromium plating solution; and conducting a second electrolysis to effect the electrolytic oxidation in said anode compartment and to effect the electrodialysis of the chromic acid values in said cathode compartment to transfer and extract the chromic acid values into said anode compartment while the iron values precipitate in the cathode compartment as the hydroxide, thereby increasing the chromic acid concentration in said anode compartment to a predetermined level.

Claim 5

A process as claimed in claim 1 wherein an aqueous chromium chromate complex solution which is free of iron value and is obtained by a complete reaction between an exhausted chromium-plating solution and a sludge which includes mainly chromium hydroxide and is obtained by reducing and neutralizing a diluted chromium-plating waste liquor is added to the solution in the anode compartment for at least one of the first electrolysis and the second electrolysis; and a reaction mixture which includes chromim chromate complex and iron values and is obtained by an incomplete reaction between an exhausted chromium-plating solution and a sludge which includes mainly chromium hydroxide and is obtained by reducing and neutralizing a diluted chromium-plating waste liquor is added to the solution in the cathode compartment for at least one of the first electrolysis and the second electrolysis.

Claim 6

A process as claimed in claim 2 wherein an aqueous chromium chromate complex solution which is free of iron value and is obtained by a complete reaction between an exhausted chromium-plating solution and a sludge which includes mainly chromium hydroxide and is obtained by reducing and neutralizing a diluted chromium-plating waste liquor is added to the solution in the anode compartment for at least one of the first electrolysis and the second electrolysis; and a reaction mixture which includes chromium chromate complex and iron values and is obtained by an incomplete reaction between an exhausted chromium-plating solution and a sludge which includes mainly chromium-plating solution and a sludge which includes mainly chromium hydroxide and is obtained by reducing and neutralizing a diluted chromium-plating waste liquor is added to the solution in the cathode compartment for at least one of the first electrolysis and the second electrolysis.

Claim 7

A process as claimed in claim 1 wherein said exhausted iron containing chromium-plating solution has a sulfuric acid content of about 2.5 grams per liter.