Synthesis and characterization OF Ca, Pb, Zn, Cu and Cd chlorapatites and Pb-Cd chlorapatites solid solutions

Abstract

The only minerals among divalent metal chlorapatites are: chloroapatite Ca 5 (PO 4 ) 3 Cl and pyromorphite Pb 5 (PO 4 ) 3 Cl. To date, no occurrence of zinc, copper and cadmium chloroapatites have been noticed in hypergenic environment. Literature provides only scattered information about hydrothermally synthesized Zn and Cd chlorapatites. There is also no data on solid solutions of Pb and Cd in chlorapatites. The purpose of this research was aqueous synthesis of calcium, lead, zinc, copper and cadmium chlorapatites. Additionally, solid solutions of Pb- and Cd-apatites (Pb 5-x Cd x ) (PO 4 ) 3 Cl (x from 0 to 5) were prepared. Syntheses were prepared in aqueous solutions at normal conditions by mixing metal nitrates Me(NO 3 ) 2 (Me = Ca, Pb, Zn, Cu, Cd), potassium phosphate KH 2 PO 4 and sodium chloride NaCl in proportions matching the stoichiometry of expected product. The precipitates were characterised by X-ray diffraction, infrared spectroscopy and scanning electron microscopy with EDS microanalyser. Partial substitution of Pb 2+ by Cd 2+ ions in the structure of pyromorphite was observed only in the range of Pb 5 (PO 4 ) 3 Cl – (Pb 4 Cd 1 )(PO 4 ) 3 Cl. However, instead of expected Zn, Cu and Cd chlorapatites, precipitation of hopeite Zn 3 (PO 4 ) 2 ∙4H 2 O, libethenite Cu 2 (PO 4 )OH, and cadmium phosphate Cd 5 H 2 (PO 4 ) 4 x 4H 2 O was observed.