Application of electrodialysis to extend the lifetime of commercial electroplating baths

摘要

Electrodialysis has been investigated as a method to extend the lifetime of industrial electroplating solutions via the selective removal of inert electrolyte salts that build up during electroplating operations. The electrodialysis measurements were made using a commercially available plate-and frame-type cell and various combinations of Nafion cation ''change and either Tosflex or Neosepta anion exchange membranes. Two commercial plating solutions were studied: a zinc-tin bath in which there is a buildup of excess potassium hydroxide and a nickel-tungsten bath characterized by a buildup of excess sodium sulfate. Potassium 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 anolyte strip and sulfuric acid in the catholyte strip, and a two compartment configuration with sulfuric acid in the catholyte strip and the anode placed directly in the plating solution. In both cases potassium hydroxide was stripped from the plating solution at greater than 94% current efficiency, but at a slightly greater voltage in the three compartment cell due to increased resistance caused by the extra membrane. A three compartment configuration was used to remove sodium sulfate from the nickel-tungsten bath, with acid solution in the catholyte and alkaline solution in the anolyte. Current efficiencies for salt removal were high but with appreciable loss of tungsten and nickel to the strip solutions. (ERA citation 19:033588)