Recovery of chromium(VI) in wastewater using solvent extraction with amide

The chromium-containing industrial wastewater, as a type of common widespread hazardous waste, causes many environmental issues. This study aimed to develop a novel amide as extractant and evaluate its recovery of chromium(VI) in aqueous solutions. Comparing nine amides with different alkyl groups and six diluents with different polarity, 40% (v/v) C14H29NO and 60% (v/v) D80 were found to be the best composition of extractant solution. Meanwhile, batch-wise experiments were performed to investigate the influence of various operating variables on the extracting, scrubbing and stripping behavior. The results demonstrated that 99.67% chromium could be extracted after six-stage countercurrent extraction, almost all impurity ions such as Na, V, Al and Mg could be removed from the loaded organic phase after three-stage cross-current scrubbing and 95.72% chromium could be stripped after six-stage countercurrent stripping respectively under the optimum conditions. The Cr2O3 product with 99.01% purity was obtained and total chromium recovery from the chromium(VI) waste solution was 95.40%. Chromic and dichromate acid were extracted by forming neutral and ion association complexation with amide C14H29NO, respectively. Finally, thermodynamics and the possible structure of chromium extraction compounds were elaborated. It is believed that this established method is promising way for the treatment of chromium-containing industrial wastewater.