Adsorption of phosphate from aqueous solutions onto zirconium loaded activated carbons derived from lignocellulosic residues

Abstract

Activated carbons from raw materials of lignocellulosic residues such as rice straws, cedar bark, and waste cardboard sludge were prepared by carbonizing the raw materials under N2 atmosphere at 673-1273 K for 1-12 h, followed by activation under CO2 atmosphere at 973-1173 K for 0.5-6 h. Zr-loaded activated carbons were also prepared from them by a conventional impregnation method using zirconium oxynitrate solution. The obtained carbon samples were characterized by N2 adsorption and XRD. Development of microporosity in the activated carbons was dependent upon the precursors and the activation conditions employed. The as-plot and pore size distribution analyses exhibited that loading of Zr species on the activated carbons in this study did not give significant influences on the microporosity of the activated carbons. A quantitative adsorption of phosphate on the Zr-loaded activated carbons was achieved below pH 9. It was found that the adsorption of phosphate on both activated carbons and Zr-loaded samples was fitted satisfactorily to Langmuir adsorption isotherms. Phosphate adsorption capacities of Zr-loaded activated carbons from rice straws and waste cardboard sludge were evaluated to be 11.1 and 5.97 mg-P g-1, respectively, which were larger than those of relevant activated carbons used as supports. Application of Dubinin-Radushkevich analysis to the phosphate adsorption isotherms indicates that the adsorption mainly proceeds through an ion exchange mechanism. © 2011 Soc. Mater. Eng. Resour. Japan.