Adsorption Of Cr(?) By Acidosasa Edulis Shoot Shell In Aqueous Solution

With the fast development of modern industry,a great quantity of wastewater containing chromium was generated.The problem faced by environmentalist nowadays is how to treat wastewater containing chromium cheaply and effectively especially in low concentration wastewater.As a heavy metal treatment technology,biosorption has many advantages,such as abundant resource,low-cost,eco-friendly,without second pollution and efficiency at low concentration,which makes biosorption has a wide application prospect.Acidosasa edulis shoot shell(AESS)is an agricultural waste found abundantly in Fujian province.Our early research indicated that AESS is a potential biosorbent for the removal of Cu(?).In the present study,AESS was used as a biosorbent to remove the anions of Cr(?)from aqueous solution.The effects of pH,adsorbent dosage,initial Cr(VI)concentration,contact time and temperature were studied by static adsorption method.The biosorption experimental data were analyzed by isotherm models,kinetic models and thermodynamic parameters to better understand the characteristics of biosorption.The biosorption mechanism was investigated by constitution analysis,functional groups determination,point zero charge determination,specific surface area analysis,element analysis,SEM and FTIR.The main conclusions were as follows.(1)The acidosasa edulis shoot shell could be used as a biosorbent for Cr(VI)ions removal from aqueous solution.The maximum adsorption capacity is 24.854 mg·g-1.(2)The porosity of AESS is helpful for the adsorption.The hydroxyl and carboxyl groups present on the surface of AESS are the active groups to adsorb Cr(VI).Electrostatic attraction and inner-sphere complex are the main adsorption mechanism.(3)The adsorption capacity increased with the concentration of H+,the maximum adsorption capacity occurred at pH 1.0.The adsorption capacity decreased with the increasing adsorbent dosage,but the removal rate increased with the increasing adsorbent dosage.The adsorption capacity increased with the initial Cr(VI)ions concentration.At the beginning,the adsorption was rapid,and then slows.Finally the equilibrium was reached.Increasing temperature is contributed to the adsorption.(4)The kinetics data were best described by the pseudo-second-order model.The initial adsorption rate increased with the increasing solution acidity and temperature.The fitting of Elovich model suggested that the adsorption process was mainly controlled by chemisorption.The fitting results of intra-particle model indicated that the intra-particle diffusion was not the sole rate-controlling step.Freundlich and Temkin isotherm models both described the equilibrium data well.(5)Negative value of ?G0 indicated the biosorption process was spontaneous.The positive value of ?S0 suggested the increased randomness at the solid/solution interface after adsorption.The value of ?H0 was determined to be 155.937kJ·mol-1,which demonstrated that the biosorption was endothermic and mainly followed the chemical process.