Removal of Phosphate Anions from Aqueous Solutions Using Polypyrrole-Coated Sawdust as a Novel Sorbent

This work was focused on the removal of phosphate ions using polypyrrole-coated sawdust as a nowel cost-effective sorbent. The phosphate uptake followed the Langmuir sorption isotherm, and the sorption capacity at 20, 35, and 50 degrees C was found to be 17.33, 23.41, an(30.39 mg/g, respectively; this indicated favorable sorption at higher temperatures. The kinetic uptake data were modeled with the Lagergren equation, first-order and second-order kinetic models, and the simple Elovich model. The results indicated that the Lagergren model best described the uptake data. The intraparticle diffusion coeffieint, as determined for 250-211- and 630-600-mu m sorbent particles at 20 degrees C, was found to be 287.3 x 10(-2) and 228.3 x 10(-2) mg g(-1) min(-1), respectively. The intraparticle diffusion was also confirmed with the Bangham equation. The sorption mean free energy, calculated with the Dubinin-Radushkevich equation, was found to be 10.98 kJ/mol, thus confirming an ion-exchange regulated sorption process. The positive value of the enthalpy change (i.e., 4.23 kJ/mol) confirmed the endothermic nature of the sorption process. The negative values of the change in the standard free energy were indicative of the spontaneous nature of the sorption process. Finally, the activation energy of the sorption process for 250-212-mu m particles, determined with the Arrhenius equation, was found to be 41.68 J/mol. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111:3081-3088,2009