Biosorption of Cr(VI) by corn stalk biomass:thermodynamics and mechanism

Corn stalk powder was used as a biosorbent for Cr(Ⅵ) aqueous solution to investigate its Cr(Ⅵ) removal capacity.The effect of experimental parameters,such as pH,sorbent dosage and temperature were examined and the optimal experimental conditions were determined.The results showed that reduction of Cr(Ⅵ) to Cr(Ⅲ) occurred during the adsorption process and 97.77% of Cr(Ⅵ) was removed by adding 0.5 g corn stalk powder into 50 mL solution which contained 50 mg·L-1 Cr(Ⅵ) under pH 1.0,30℃,200 r·min-1 and 3 h contact time.The adsorption capacity increased with temperature.Langmuir,Freundlich and Dubinin-Radushkevick isotherms were used to fit the adsorption equilibrium data and the adsorption process followed the Langmuir isotherm adsorption model.The adsorption capacity of the biosorbent was 14.46 mg.g-1,which is higher or comparable to the adsorption capacity of various adsorbents reported in the literature.Thermodynamic parameters of the adsorption process,such as ΔG0,ΔH0 and ΔS0,were calculated and the results indicated that the overall adsorption process was endothrmic and spontaneous.Finally,the removal mechanism is discussed by deduction from the experimental results,FTIR,and SEM images.The adsorption of Cr(Ⅵ) coexists with the redox process,and the corn stalk powder is a potential biosorbent which could be used in treatment of chromium contaminated wastewater.