Biosorption Of Cr(VI) From Aqueous Solution By Wheat Bran And Rice Bran

Hexavalent chromium-containing wastewater, which was harmful to natural environment and human being health, has widespread sources and great toxicity. In recent years, considerable attention has been devoted to the study of removal of heavy metal ions from solution by biosorption using agricultural materials such as nut wastes, tree barks and sawdust. Wheat bran and rice bran are widely available and low-cost agricultural by-products, some researches have found that wheat bran and rice bran are excellent biosorbents for cations. However, at the present time no information concerning the biosorption of anion onto wheat bran is available in literature. Therefore, the objective of this study is to investigate the removal of Cr(VI) from synthetic aqueous solutions by wheat bran and rice bran. The effect of different parameters such as pH, time, sorbent dose, Cr(VI) initial concentration, particle size, pretreatment method and common co-exist ions was investigated. Several kinetics and isotherm sorption models were used to represent the experimental data, furthermore, the activation energy and heat of sorption were also calculated, at last, sorption mechanism of Cr(VI) by WB was discussed.Cr(VI) removal was found to be maximum at pH=1.0, the rate of biosorption at the beginning is very fast , then slowly ran up to equilibrium, the amount of Cr(VI) sorbed increased with increasing WB′particle size and decreasing RB'particle size, and the common co-exist ions have no effect on the removal of Cr(VI).Heat, acid and hard alkali pretreatment methods were found to increase the biosorption capacity of RB, however, mild alkali, inorganic salts and organic compounds decrease the biosorption capacity of RB The amount of Cr(VI) sorbed decreased with increasing sorbent dose, and increased with increasing Cr(VI) initial concentration, however, the change of Cr(VI) removal efficiency is reverse.Pseudo-second-order model was found to explain the kinetics of Cr(VI) adsorption most effectively, and the rate constants of which at different initial concentration of Cr(VI),different dose of sorbent, and different temperature were calculated. The kinetics data for Cr(VI) sorption onto WB and RB were also analyzed according mass transfer and intraparticle diffusion models in order to increase sorption process understanding. Equilibrium datas fit the Langmuir isotherm model very well, which shows the monolayer coverage of the sorbate on the surface of WB, and the values of RL indicates that biosorption of Cr(VI) is favorable on WB. On the other hand, equilibrium datas fit the Freundlich isotherm model very well, and the values of 1/n also indicates that biosorption of Cr(VI) is favorable on RB. Ea=36.8kJ/mol, and△H0=35.3kJ/mol, which showed that the sorption is a chemical sorption process.Compared with raw WB, the removal of Cr(VI) decreased after chemical treatment, and combined with FTIR, it was concluded that the hydroxy and amido play a great role during the process of biosorption. Cr(VI) was biosorbed with the form of HCrO4- by electrostatic attraction. Change of Cr(VI),total Cr concentration and pH in biosorption process revealed the mechanism of oxidation-reduction and cation exchange during biosorption.