Immobilization of Fluorine in Reduced Slag by Addition of Crystalline Hydroxyapatite and Glassy Calcium Phosphate Using a Calcining Process

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The ability of a variety of hydroxyapatite (HAp) sources, including animal bone and calcium phosphate glasses, is demonstrated to immobilize fluorine in slag through calcining processes. The slowly cooled slags were calcined in a furnace along with hydroxyapatite, animal bone, and calcium meta-phosphate glasses. As a result, fluoro-hydroxyapatite was formed, confining the fluorine ions in the formed crystal, leading to the suppression of the dissolution of fluorine ion. Each of the samples demonstrated a low elution of fluorine ions (less than 0.8 ppm), measured by leaching method. The quantity evaluation of formed apatite-like crystal and other subsidiaries were conducted for the treatments by adding recycled animals’ bones as the source of calcium phosphate, as well as reagent HAp and meta calcium phosphate glasses.

Fig. 9 Schematic of fluorine confinement in HAp crystals allowing for the alternation of stable fluoro-apatite (FAp) crystal.