| EPA's pollution prevention and waste reduction policies encourage the regeneration and recycling of spent chromium plating baths. One approach used successfully in the past is electrolytic regeneration. The efficiency of this process depends on the efficiency of the removal of contaminants from anolyte, which depends on the type of electrode used, the amount of applied current, and the types of separators used. Among these factors, the type of separator used is most important because transport of the impurity through the separator is crucial for the electrolytic regeneration processes to be successful.; The transport properties of the impurities (Cu(II), Ni(II), and Fe(III)) through the separators used in these processes are poorly understood. Therefore, in this research, studies of the transport properties (diffusivity, conductivity, and mobility) of contaminants through the separators (Nafion 117 membrane and ceramic diaphragm) were investigated. The partition coefficients of the contaminants in the separators were also determined since they impact their transport rate. For the Cu(II), Ni(II), and Fe(III) in the Nafion membranes, their partition coefficients were 0.6, 0.59, and 0.51, respectively in single ion partitioning experiments; 0.57, 0.58, and 0.40, respectively in multiple ion partitioning experiments. The partition coefficients of bisulfate and Cr(VI) in the Nafion membrane were about 0.21 and 0.14, respectively.; It was found that partitioning was well characterized by a Freundlich isotherm. In the Nafion membrane, cationic partitioning decreased with decreasing pH. The partition coefficients of the three impurity species in the ceramic diaphragm were approximately the same (0.4). Trivalent impurity cations had a higher affinity for the Nafion membrane than divalent cations. This partly accounted for that the trivalent cation (Fe(III)) having smaller diffusion coefficients than the divalent cations. The diffusivities measured were in the order of Cu(II) > Nii(II) > Fe(III) in both separators. For the Nafion membrane, they were 1.04 × 10−6, 8.36 × 10−7, and 4.24 × 10−7 cm 2/sec, respectively in single ion diffusion experiments; 1.18 × 10−6, 1.09 × 10−6, and 5.56 × 10−7 cm2/sec, respectively in multiple ion diffusion experiments. For the ceramic diaphragm, they were 3.64 × 10−6, 3.04 × 10−6, and 1.68 × 10−6 cm2/sec, respectively in multiple ion diffusion experiments. The diffusion coefficients of bisulfate and Cr(VI) through the Nafion membrane were 1.08 × 10−6 and 8.06 × 10−7 cm2/sec, respectively. Temperature did not affect on the cation partitioning in the Nafion membrane; however, increasing temperature increased diffusivity according to the Arrehnius equation. The impurity cation diffusivity also increased with decreasing pH. (Abstract shortened by UMI.)... |
