Simultaneous removal of cadmium from kaolin and catholyte during soil electrokinetic remediation

The influence of the pH variation of a catholyte on the removal of Cd from kaolin and the subsequent precipitation of the Cd in the catholyte was evaluated during soil electrokinetic remediation (EKR). The pH variations of the catholyte were induced by the injection of nitric acid (HNO3) at different concentrations (0.00, 0.01, 0.06, 0.12, 0.18, 0.24, 0.42 M) at a constant rate (0.6 ml/h). The addition of the acid enhanced the removal of Cd from kaolin. When the concentration of the injected HNO3 was higher than 0.06 M. both the electrical energy and acid consumption increased. When the concentration of the injected acid was higher than 0.12 M, the pH in the catholyte markedly increased. The best results were obtained by using 0.06 M HNO3. At this concentration, it was possible to extract 98% of the Cd from kaolin, of which 63% precipitated in the catholyte. Thirteen liters of HNO3 and 30 kW-h of electrical energy were required per cubic meter of treated kaolin. The average extraction rate of Cd was extracted from kaolin reached high values (0.38 mg/h) when less than 90% of the Cd had been removed. For the remaining 10%, the extraction rates noticeably decreased (0.025-0.059 mg/h). (c) 2012 Elsevier B.V. All rights reserved.