Removal of Phosphate from Aqueous Solution Using Hydrotalcite/Chitosan Composite

Excess of phosphate in water bodies is harmful to aquaculture and to the human beings. Thus it is necessary to remove phosphate from effluents discharging into waste water systems and also drinking water when it exceeds the limit. In this study, adsorption behaviours of phosphate over hydrotalcite/chitosan (HT/CS) composite have been examined using kinetics and thermodynamics data. Hydrotalcite (HT) possesses the phosphate adsorption capacity which could be further enhanced by making it as composite with chitosan that contributes its positive sites for phosphate sorption. Effect of parameters such as contact time, dosage of adsorbent, pH of the aqueous solution, co-anions and temperature on the sorption of phosphate on HT/CS were studied. Removal of phosphate aqueous solution follows pseudo-second-ordermodel. The diffusion of sorbate is controlled by pore diffusion model. Adsorption isotherm is well fitted with Langmuir, Freundlich and Dubinin-Radushkevich adsorption isotherms. The adsorption capacity of phosphate (Q(0)) derived from Langmuir isotherm was 57.87 mg/g. The positive Delta H-0 value revealed that the adsorption process is endothermic. Negative value of Delta G(0) and positive value of Delta S-0 suggests the spontaneous nature of adsorption process. The adsorbent was characterized using SEM with EDX and FTIR studies before and after adsorption of phosphate. The adsorption of phosphate over this composite is very quick, efficient and 99.5% phosphate removal occurs within half an hour using 0.25 g of composite.