Effective utilization of the functional groups in chitosan by loading Zn(II) for the removal of nitrate and phosphate.

Chitosan beads cross-linked with glutaraldehyde were loaded with Zn(II) for the removal of nitrate and phosphate. The Zn(II) was bound by the free amino groups in the cross-linked chitosan beads. In order to utilise the hydroxyl groups on cross-linked chitosan, it was carboxylated with chloroacetic acid and then loaded with Zn(II). Both the sorbents viz. zinc-loaded cross-linked chitosan beads (ZnCB) and zinc-loaded carboxylated cross-linked chitosan beads (ZnCCB) were characterised by SEM, EDAX, X-ray diffraction and FT-IR. Adsorption studies were carried out in batch mode. The maximum adsorption capacity of ZnCB and ZnCCB for nitrate was 27.56 and 59.00 mg/g, respectively and for phosphate it was 31.45 and 67.50 mg/g, respectively. The suitability of the Freundlich, Langmuir and Dubinin–Radushkevich adsorption models to the adsorption equilibrium data was investigated. The equilibrium data obtained for nitrate and phosphate removal using ZnCCB were found to follow Freundlich adsorption isotherm. The thermodynamic parameters were evaluated. The results showed that the adsorption process was spontaneous, endothermic and entropy driven. [ABSTRACT FROM PUBLISHER]