Nafion-117 Behavior during Cation Separation from Spent Chromium Plating Solutions

Abstract

This study investigated the behavior of Nafion-117 ion-exchange membranes that are commonly used as the separator in electrolytic regeneration of spent chromium plating solutions. In the co-presence of Cu2+, Ni2+, and Fe3+ impurities (∼0.01−0.1 M) in ∼0.5−2.0 M H2CrO4, the exchange equivalents of Ni2+ by Nafion-117 was double that of Cu2+ (0.02 mmol of H+/(g of Nafion)) but smaller than that (∼0.03−0.15 mmol of H+/(g of Nafion)) of Fe3+, exhibiting the order Fe3+ ≥ Ni2+ ≥ Cu2+ in Nafion affinity. The water content (∼41%) of a Nafion-117 membrane soaked in 2 M H2CrO4 was greater than those (∼35−38%) in the contaminated 2 M chromic acid solutions, whereas the porosity (0.24) of the former was smaller than those (0.29−0.37) of the latter. For the Nafion-117 in 2 M chromic acid solutions with/without cation impurities, (1) the tortuosity coefficient of Fe3+ was about 1.8 times that of Cu2+ or Ni2+, (2) the calculated pore radius was 3.2 nm for a multiimpurity case (0.1 M Cu(II), Fe(III), Ni(II), and Cr(III) e...