Synthesis of nano-sized hydrocalumite from a Gastropod shell for aqua system phosphate removal

Material with high affinity for oxyanions, Hydrocalumite (HC), was synthesized using a waste biogenic resource as a precursor and its ability to remove phosphate from aqua system was studied. The synthesis of HC samples with particle sizes that ranged between 116 and 135 nm was confirmed by XRD analysis. High correlation coefficient values (r2 = 1.000) were obtained when the time-concentration profile data were fitted to the pseudo second order kinetic model. The formation of supersaturated Ca and Al phosphate salts were confirmed by the positive saturation index values and the feasibility of precipitate formation by the supersaturated salts were confirmed by the thermodynamic parameters (i.e. ΔG < 0). Process variables optimization (pH, ionic strength and organic load) had nominal influence on the magnitude of phosphate removal. The fractionation of the phosphate laden HC (PHC2) showed that the greater percentage (>99%) of the phosphate was distributed within the calcium matrix. Comparison of the EDAX spectra of the virgin HC with the PHC2 showed that anion exchange could also be a player in phosphate removal by the HC.