Conversion of calcium sulfite waste to hydroxyapatite

Calcium sulfite waste was successfully transformed to hydroxyapatite (HAp) by oxidation using H2O2, followed by reaction with (NH4)2HPO4 under an NH4OH atmosphere. A single phase hydroxyapatite was obtained by stirring at 60, 80, or 100 °C rather than by hydrothermal treatment at 150 °C. Such formation implied that the homogeneity of the solution was very important. The primary HAp particles obtained had columnar shape, which formed spongy secondary particles with a diameter of around 1 μm. Such porous particles resulted from the dissolution rate of calcium sulfite. The HAp obtained had a relatively Ca-rich composition of around Ca/P = 1.71, and the specific surface area was around 69 m2/g. In adsorption tests for Cs+ and Cd2 + cations in artificial seawater, the prepared HAp, like the general HAp powder, could remove Cd2 + cations from the seawater.

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► Calcium sulfite waste was succeeding to be converted to hydroxyapatite.
► The prepared hydroxyapatite has rod-like primary particle with Ca-rich composition.
► The hydroxyapatite can remove Cd cation in the artificial sea water.