Equilibrium and kinetics of adsorption of phosphate onto iron-doped activated carbon

Wang, Zhengfang; Nie, Er; Li, Jihua; Yang, Mo; Zhao, Yongjun; Luo, Xingzhang; Zheng, Zheng

Equilibrium and kinetics of adsorption of phosphate onto iron-doped activated carbon

2012

PURPOSE: Two series of activated carbons modified by Fe (II) and Fe (III) (denoted as AC/N-Feᴵᴵ and AC/N-Feᴵᴵᴵ), respectively, were used as adsorbents for the removal of phosphate in aqueous solutions. METHOD: The synthesized adsorbent materials were investigated by different experimental analysis means. The adsorption of phosphate on activated carbons has been studied in kinetic and equilibrium conditions taking into account the adsorbate concentration, temperature, and solution pH as major influential factors. RESULTS: Maximum removals of phosphate are obtained in the pH range of 3.78–6.84 for both adsorbents. Langmuir isotherm adsorption equation well describes the experimental adsorption isotherms. Kinetic studies revealed that the adsorption process followed a pseudo-second order kinetic model. Results suggest that the main phase formed in AC/N-Feᴵᴵ and AC/N-Feᴵᴵᴵ is goethite and akaganeite, respectively; the presence of iron oxides significantly affected the surface area and the pore structure of the activated carbon. CONCLUSIONS: Studies revealed that iron-doped activated carbons were effective in removing phosphate. AC/N-Feᴵᴵ has a higher phosphate removal capacity than AC/N-Feᴵᴵᴵ, which could be attributed to its better intra-particle diffusion and higher binding energy. The activation energy for adsorption was calculated to be 22.23 and 10.89 kJ mol⁻¹ for AC/N-Feᴵᴵ and AC/N-Feᴵᴵᴵ, respectively. The adsorption process was complex; both surface adsorption and intra-particle diffusion were simultaneously occurring during the process and contribute to the adsorption mechanism.

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