SELECTIVE LIQUID-SOLID EXTRACTION OF Cr (III) FROM Cr (III) AND Fe (III) MIXTURE BY CHELEX 100 RESIN

Abstract

This work focuses on the liquid-solid extraction of the mixture chromium (III) and iron (III) by the resin Chelex 100. The influence of operating parameters as equilibrium time (2 to 45 min), the initial pH of aqueous solution (1.06 to 3.97), effect of initial chromium (Ш) and iron (III) concentrations (100 to 500 ppm), effect of temperature (295 to 328 K) and the effect of ionic strength (NaCl, KNO3) was studied. The extraction yields of and the capacities of sorption of Cr (III) and Fe (III) by the resin Chelex 100 were determined at 64.94 and 87.30 % equivalent to 11.6 and 10.94 mg∙g-1 respectively. The equilibrium time was 45 and 5 min for initial concentrations of the mixture of Cr (III) and Fe (III) 500 mg∙L-1 respectively. The kinetic model of the pseudo second order describes the sorption process for the two metals. The separation of two metals is maximal at 100 mg∙L-1 and in the presence of KNO3 0.1 M. The thermodynamic study showed that the extraction process is exothermic (-29223 and -20735.1 kJ∙mol-1 for Cr (III) and Fe (III) respectively) and the negative ΔG values show that, the sorption of metals occurs spontaneously in 295 - 328 K, while it is not appropriate in case of Fe (III) as indicated by the positive sign of ΔG (96 kJ∙mol-1) at 309 K. The percentage of desorption is estimated to 57.6 % for both metals by the solution of HNO3 1 M. The experimental results obtained showed the validity of the liquid-solid extraction to be used for selective extraction and concentration of Cr (III) from the Cr (III) and Fe (III) mixture solutions.

Keywords

• Chelex 100
• diffusion models
• kinetic models
• liquid-solid extraction
• thermodynamic parameters