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Extended Study of Sunflower Straw in the Selective Adsorption Behaviors and Mechanisms for U( VI) and Pb( Ⅱ)

AI Lian;LUO Xue-gang;LIN Xiao-yan;MEI Qiang;School of Materials Science and Engineering,Southwest University of Science and Technology;Engineering Research Center of Biomass Materials,Ministry of Education;Southwest University of Science and Technology;  
The adsorptive properties of sunflower straw for U( VI) and Pb( Ⅱ) were systematically evaluated in single and binary solutions using batch experiments as a function of solution pH,adsorbent dosage,contact time and initial ion concentration. The kinetic data were analyzed by the pseudo-first-order, pseudo-second-order kinetic and intraparticle diffusion models. The equilibrium sorption data were examined using the Langmuir and Freundlich isotherm equations. It was shown that that a dose of 2. 0 g / L of sunflower straw in an initial ions concentration of 20 mg / L with an initial pH of 4. 0 and a contact time of 720 min resulted in the maximum U( VI) and Pb( Ⅱ) removal efficiency( about 77. 55 % and 87. 44 %,respectively) in U( VI) / Pb( Ⅱ) binary system. The kinetic and isotherm experimental data were fitted to the pseudo-second-order rate equation and the Langmuir isotherm model with much satisfaction for single and binary metal systems,respectively. The sorption data of Pb( Ⅱ) also conformed successfully to the Freundlich equation at U( VI) concentration more than 200 mg / L. The maximum adsorption capacity in single system for U( VI) and Pb( Ⅱ) was calculated to be 327. 0 and 67. 59 mg / g,respectively. The sunflower straw displayed an excellent selectivity in the adsorption of Pb( Ⅱ) over U( VI) in the binary system at lower initial concentrations of ions and the case was vice versa at higher concentrations. Furthermore,SEM,EDX and FT-IR analyses revealed that U( VI) and Pb( Ⅱ) adsorption onto sunflower straw could be predominantly controlled by the ion exchange as well as complexation mechanism.
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