Conversion of the echinoderm Mellita eduardobarrosoi calcite skeleton into porous hydroxyapatite by treatment with phosphated boiling solutions

The influence of the boiling solution technique (a nonhydrothermal wet treatment) in the formation of hydroxyapatite (HA) from a novel source, an echinoderm known as Mellita eduardobarrosoi, whose skeleton contains calcite as an inorganic constituent, was investigated. The experimental plan explores the conversion using a batch boiling system composed of KH2PO4 + KOH aqueous solutions at initial pH's of 8, 9, 10; 11, and 12, where granules of skeleton were dispersed to yield PO4/CaCO3 ratios of 1.0, 1.5, and 2.0. Chemical and X-ray diffraction analysis of the resulting material showed that the conversion of calcite by this technique is almost always higher than 70%, pH's 10 and 11 yielding the highest conversion. Depending on the operating conditions, the obtained material is a mixture of the original calcite and HA of varying stoichiometry and composition. Nevertheless, the interconnected porosity is preserved.