Ion-exchange membrane fouling by boric acid in the electrodialysis of nickel electroplating rinsing waters: generalization of our results

Abstract

This research investigated electrodialysis membrane fouling (EDMF) by boric acid during nickel salts electrodialysis (ED). This process is used in the nickel electroplating (EP) industry to concentrate and reuse nickel salts and to recycle treated rinse waters. Boric acid is an essential component of the nickel EP bath (Watts bath). Membrane fouling by organics (e.g., brighteners) is a well known and well investigated problem. However, the electrodialytic behavior of boric acid has not been extensively studied. Unexpected fouling problems have been observed in some Ni electroplating plants; each morning, at the start-up of the electrodialyzer, the resistance of the ED stack increases dramatically. We suspected the boric acid, and preliminary laboratory tests confirmed our hypothesis. Membrane fouling was obtained with a mixture of Na 2SO 4/H 3BO 3. This test confirms that the fouling is not due to any metal hydroxide deposits or any organic additive from the Watts bath. The fouling was then systematically investigated with the main components of the Watts bath (nickel sulfate and chloride) in the presence of boric acid. Tests with CuSO 4 confirmed the fouling effect of this acid. NiSO 4 and NiCl 2 present opposite behaviors during ED. This difference is accentuated in the presence of H 3BO 3. The EDMF is more severe with NiCl 2. Why? We have explained this result by the difference of counterion mobilities in their respective membranes. We try to generalize this result to other EDMF, particularly by natural organic matter.