10 Towards a Safer Environment：（7）How apatite minerals remediate Pb,Zn and Mn from wastewater？

To evaluate the effectiveness of apatite mineral in removing different contaminants from low quality water in the industrial city of abha,Asir region,southwestern of Saudi Arabia two phosphatic clay dominated by apatite mineral were selected.In situ remediation experiment proved that apatite mineral has the highest affinity for Pb and removed more than 94% from initial Pb concentration.The rest of contaminants followed the descending order of:Zn>Mn>Cu>Co>Ni.The sorption of Pb,Zn and Mn onto apatite mineral was well characterized by the Langmuir model.Ternary-metal addition induced competitive sorption among the three metals,with the interfering effect of Pb>Zn>Mn.During metal retention by apatite mineral calcium and phosphate were determined in equilibrium solution.Calcium increased and phosphate decreased with increasing metal disappearance.The greatest increase of calcium and the largest phosphate reduction were found with Pb+2 sorption. This is suggested that Pb+2 retention by apatite was through the dissolution of apatite which mean release of Ca and P into solution and formation of pyromorphite(lead phosphate)as consuming of P.Obtained results suggested that there are two general mechanisms for the ability of apatite mineral to take up Pb2+,Zn+2 and Mn+2.The first is (ion-ion exchange mechanism)concerned with adsorption of ions on the solid surface followed by their diffusion into apatite mineral and the release of cations originally contained within apatite.The second is (dissolution- precipitation mechanism)concerned to the dissolution of apatite in the aqueous solution containing Pb2+,Zn+2 and Mn+2 followed by the precipitation or coprecipitation.Pb+2 desorption responding to solution pH may indicate that not all the Pb+2 was chemisorbed and fraction of Pb+2 was weakly adsorbed or complexed on the surface of apatite mineral.