Comparative biosorption of chromium (VI) using chemically modified date pits (CM-DP) and olive stone (CM-OS): Kinetics, isotherms and influence of co-existing ions

Chemically modified date pit (CM-DP) and olive stone (CM-OS) were studied for their biosorption capacity for hexavalent chromium (Cr(VI)) removal in the aqueous phase. The effect of changing the process conditions, such as the initial Cr (VI) concentration, pH, biosorbent dosage, ionic strength, presence of other ions and temperature were investigated. It showed that at pH = 2, biosorbent dosage > 4 g/L and a low ionic strength, both biosorbents showed best biosorption capacity of the Cr(VI) removal. Various isotherm models were applied to fit the experimental data and the Freundlich isotherm model was the best fitting isotherm model for the biosorption experimental data of both biosorbents. The maximum biosorption capacities of CM-DP and CM-OS were found to be 82.63 and 53.31 mg/g respectively, which is comparable to other materials. In the kinetic study, the pseudo second order model can best describe the biosorption process of both biosorbents and the intraparticle diffusion was not the rate-limiting step indicating the contribution of film diffusion in the Cr(VI) removal processes.