The removal of chromium (VI) from aqueous solutions by activated alumina has been investigated as a function of solution pH, initial chromium concentration, adsorbent dose of activated alumina and temperature. The pH and the adsorbent dose of activated alumina are the most significant parameters affecting chromium (VI) adsorption. The chromium concentrations were analyzed by reaction with 1,5-diphenylcarbazide. This method has been validated according to the French standard XPT-90-210. In order to optimize the effect of the main parameters and their mutual interaction for the adsorption process, a full factor design of the type nk has been used. In this study the removal of chromium (VI) by adsorption on activated alumina was investigated and results were fitted to Langmuir, Freundlich, Dubinin-Redushkevich and Temkin adsorption models, at different temperatures. The constants of each model were evaluated depending on temperature. Thermodynamic parameters for the adsorption system were determined at 10, 25 and 40°C. The obtained values showed that Cr (VI) adsorption is a spontaneous and exothermic process. The kinetic process was evaluated by first–order, second–order and Elovich kinetic models. In second section, the removal of chromium (VI) from aqueous solutions by Donnan dialysis has been investigated. The tows AEMs: Selemion AMV and Neosepta AFN. The amount of chromium removed was determined on the basis of the following parameters: initial chromium concentration, type of anion exchange membranes, co-ion concentration and magnetic stirring. A 24 full factorial design analysis was performed to screen the parameters affecting Cr (VI) removal efficiency were examined. Using the experimental results, a linear mathematical model representing the influence of the different parameters and their interactions was obtained. Analysis of variance (ANOVA), F-test and student's t- test showed that the type of anion exchange membrane is the most significant parameter affecting chromium (VI) removal. The statistical analysis of experimental data assumes that the data come from normal distribution. Then, a modelisation of chromium removal by Donnan dialysis through anion exchange membrane, these results are compared with the theoretical predictions given by the resolution of the corrected Nernst–Planck's equation in the cases of the homogeneous models of ion-exchange membranes. This confrontation confirms the existence of three domains corresponding respectively to a complete diffusion boundary layers (DBLs) control, a mixed control and a complete membrane control of the inter-diffusion process. And finally, the Donnan dialysis and adsorption onto activated alumina has been coupled. The coupling DIC-AAA was successfully achieved with 90% of chromium removed
Removal of chromium VI from aqueous solutions by adsoprtion onto activated alumina and donnan dialysis