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

Abstract

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.