Abstract
Fluorine immobilization mechanism of apatite treatment for electric arc furnace steelmaking slag was investigated. Apatite treatment immoboilized fluorine strongly and prevented from secondary leaching of fluornie. This study found that fluorapatite formation mainly contributed to fluorine immobilization. Synchrotron X-ray diffraction analysis showed that fluorapatite was generated directly from amorphous calcium phosphate, not hydroxide/fluorine ion-exchange reaction inside hydroxyapatite. When fluorine was adsorbed to amorphous calcium phosphate, fluorapatite was synthesized soon and encapsulated fluorine inside its crystal structure. On the other hand, fluorine adsorbed to hydroxyapatite could be released easily before slow fluorapatite formation. Sodium alginate and chitosan could generate organic-apatite complex with multi-layer structure and relatively homogeneous surface. When these organic-apatite complexes could be synthesized on slag surface, however, they gave less fluorine immobilization than normal apatite treatment and promoted fluorine leaching. Competitive adsorption between fluorine and alginate/chitosan onto amorphous calcium phosphate might inhibit fluorapatite formation.
