Extractive continuous extractor for chromium recovery: Chromium (VI) reduction to chromium (III) in sustainable emulsion liquid membrane process

This work reports, for the first time, a detailed investigation on the Chromium (VI) reduction to Chromium (III) in a sustainable continuous emulsion liquid membrane process. This method is used in the treatment of authentic rinse electroplating wastewater containing 40 ppm Chromium (VI) concentration. The liquid membrane phase is composed of palm oil as diluent, Span 80 as surfactant, trioctylmethylammonium chloride as extractant, and acidic thiourea solution as an internal reagent. The statistical experimental design was applied in optimizing the process parameters for the removal of chromium by a sustainable continuous emulsion liquid membrane process. Recovery and enrichment of the less toxic Chromium (III) at optimum process conditions were further studied. Optimization of chromium removal was investigated using the response surface methodology. Within the range of the selected operating conditions, the optimized values of emulsion to an external feed phase ratio, agitation speed and retention time are found to be 1:5, 342 rpm and 170 s. For instance, 99% of Chromium could be extracted at the optimum process conditions. The recovered species of Chromium (VI) was efficiently stripped into the internal phase (82%) as less-toxic Chromium (III) using 2.0 M thiourea in 2.0 M sulfuric acid as the strippant. In the meantime, up to 200 ppm external feed phase concentration seems to be the best range of condition for the recovery process of chromium from rinse electroplating wastewater. (C) 2019 Elsevier Ltd. All rights reserved.