Crystal chemical characteristics of ellestadite-type apatite: implications for toxic metal immobilization

The ellestadite apatites Ca10[(SiO4)x(PO4)6−2x(SO4)x]Cl2 were studied by powder X-ray and neutron diffraction to establish baseline crystallographic data. These synthetic materials, unlike mineral specimens that are well equilibrated, show no Si/P/S ordering and conform to P63/m symmetry. Phosphate-rich ellestadites where 0 ≤ x ≤ 1 show chemical stability towards Toxicity Characterization Leaching Procedure (TCLP) testing and are potential immobilization matrices for mixed toxic metal wastes.Accepted versio