PHOSPHATE REMOVAL FROM AQUEOUS SOLUTION USING MODIFIED AND UNMODIFIED CRAB SHELL CHITOSAN

Abstract

Unmodified and aminated chitosan were used for the removal of phosphate from aqueous solution. The unmodified and aminated crab shell chitosan were characterized by using infra-red spectrophotometry, scanning electron microscope and X-ray diffractogram. The results show that there were IR spectra that indicated the presence of amine in the aminated chitosan. The scanning electron micrographs indicate increase porosity as a direct consequence of the loaded amine groups attached to unmodified chitosan and the maximum peaks absorption correlates with the standard XRD of chitosan. Phosphate removal was carried out under various experimental conditions by varying the pH, contact time, biomass dose, concentration and temperature. Adsorption data have been interpreted in terms of Langmuir and Freundlich equations. The results obtained provided strong support for the adsorption of phosphate onto the biomass and was found to fit sufficiently to the Freundlich isotherm but fairly to Langmuir isotherm model. The sorption kinetics was tested using the pseudo-first-order and pseudo-second order models and good correlation coefficients obtained for the pseudo-second-order kinetics model shows that phosphate uptake process followed the pseudo-second-order rate expression. Results obtained showed that maximum adsorption of 3.83mg/g and 3.92mg/g takes place at pH 3 for unmodified chitosan and aminated chitosan and the optimum time for unmodified chitosan is 120 min while that of aminated chitosan is 300 min, Varying the adsorbent biomass dosage shows increase in adsorption capacity (66.88% - 86.88% for unmodified chitosan and 76.12% - 86.34% for aminated chitosan) with increase in biomass dosage. Evaluation of thermodynamic parameters showed that the adsorption process is endothermic and non-spontaneous in nature.