THE APPLICATION OF ELECTRODIALYSIS TO EXTEND THE LIFETIME OF COMMERCIAL ELECTROPLATING BATHS

Electrodialysis has been investigated as a method to extend the lifeti me of industrial electroplating solutions via the selective removal of inert electrolyte salts that build up during electroplating operation s. The electrodialysis measurements were made using a commercially ava ilable plate- and frame-type cell and various combinations of Nafion c ation exchange and either Tosflex or Neosepta anion exchange membranes . Two commercial plating solutions were studied: a zinc-tin bath in wh ich there is a buildup of excess potassium hydroxide and a nickel-tung sten bath characterized by a buildup of excess sodium sulfate. Potassi um hydroxide was effectively removed from the zinc-tin bath with very little loss of the heavy metals. Two configurations were investigated: a three compartment configuration with potassium hydroxide in the ano lyte strip and sulfuric acid in the catholyte strip, and a two compart ment configuration with sulfuric acid in the catholyte strip and the a node placed directly in the plating solution. In both cases potassium hydroxide was stripped from the plating solution at greater than 94% c urrent efficiency, but at a slightly greater voltage in the three comp artment cell due to increased resistance caused by the extra membrane. A three compartment configuration was used to remove sodium sulfate f rom the nickel-tungsten bath, with acid solution in the catholyte and alkaline solution in the anolyte. Current efficiencies for salt remova l were high but with appreciable loss of tungsten and nickel to the st rip solutions.