TRIVALENT CHROMIUM REMOVAL BY AQUEOUS TWO-PHASE EXTRACTION WITH CHLORIDE IONS AS EXTRACTANTS.K. SUJI AND K.B. RADHAKRISHNAN
Trivalent chromium is an essential micronutrient. It is considered as the stable form of chromium. However, the conversion of trivalent to hexavalent chromium in natural conditions is reported by several investigators. Hexavalent chromium is an anthropogenic carcinogen. This necessitates the recycling of chromium from contaminated solutions. The present study focuses on the extraction of trivalent chromium to polyethylene glycol 1500 using sodium chloride as the extractant. The effect of the significant independent parameters as to the initial salt solution pH, extractant concentration and initial salt phase metal ion concentration on the extraction efficiency is studied experimentally. The optimum conditions are found out using central composite design in Minitab statistical software version 16. A second order polynomial model is proposed for the extraction efficiency as a function of the three independent parameters. The maximum efficiency obtained in the present optimization studies is 24.5% at an initial salt solution pH of 4.82, NaCl concentration 0.0035 mol/l and initial metal ion concentration 7.4 ppm. The results of the optimization studies are validated by conducting experiments at the optimum conditions. Extraction of Cr(III) using organic chelating agents may provide better efficiency, but, is not advisable due to recalcitrant and hazardous nature of chemicals involved. The system used in this study satisfies the conditions of green chemistry despite its low efficiency.