Calcium Phosphate Sorbent for Environmental Application

Heavy metal pollution in soils, wastewater or fly ashes is a persistent environmental problem. This pollution in water or wastewater is an ongoing environmental problem and the rules to control and decrease this pollution are increasingly strict. The extreme toxicity of heavy metals even at low concentration and their bio-accumulation cause a lot of environmental problems. Minerals such as the calcium phosphate of general formula M10(XO4)6 Y2 with M a divalent cation, (XO4)3- a trivalent anion and Y- a monovalent anion are well know for trapping metal ions. The retention of heavy metals by calcium phosphate has been already widely studied in aqueous solutions.In this study, a low cost calcium phosphate gel (Ca-HA) synthesized from a calcium carbonate industrial waste was used as a sorbent for wastewater treatment. We have characterized this sorbent before and after use. The physical characterization showed a decrease of the specific surface area and density. The granulometry measurements showed an increase of the particles diameter explained by the sorption of pollutants (organic molecules). The presence of these molecules was confirmed by total and organic carbon measurement and thermal analysis. The elemental measurements confirmed also the heavy metal sorption by the Ca-HA. A calcination of the contaminated Ca-HA was carried out at different temperatures. After calcination the solid contained less organic molecules and heavy metals were concentrated in the matrix.