Biosorption of Lead(II) from Aqueous Solution by Rape Straw Powders: Optimization and Mechanism Studies

In this study, the adsorption of lead(II) from aqueous solution by rape straw powders was investigated. Box-Behnken Design(BBD) accompanied by response surface methodology (RSM) were employed to optimize various environmental conditions for biosorption of pH, concentration of lead ions, particle size, biosorbents loading and contact time using rape straw powders as absorbent. The models of kinetics and isotherms were used to evaluate the behaviors of biosorbent for uptaking lead(II) from aqueous solution by rape straw powders. The functional groups of rape straw powders which played roles were recognized by Fourier transform infrared spectra. The results revealed that the parameters of pH and biosorbents loading were the key factors affecting the efficiency for the removal of lead(II) from aqueous solution. R-2 were 0. 966 4, 0. 970 1 and 0. 964 9 for uptaking lead (II) from aqueous solution by rape straw pith core, shell and seed pods, respectively, indicated the validity of the model. The experimental data was better described by a pseudo-second-order model compared with the intraparticle diffusion model. In comparing the analysis of Langmuir and Freundlich isotherms, the adsorption of lead ions showed a better fit with the Langmuir isotherm model. According to the Langmuir equation, the maximum adsorption capacities of rape straw pith core, shell and seed pods for uptaking lead(II) from aqueous solution were 135. 14, 78. 74, 90. 09 mg . g(-1), respectively. Comparing the graphs of infrared spectroscopy of straw pith core, shell and seed pods before and after the Pb(II) removal, we discovered that the spectra changed, particularly active groups, such as hydroxy, carboxyl and amide groups of the protein, which played major roles in the biosorption process. The study of results provided evidences that rape straw powders can be used for removing Pb (II) from sewage water.