ワラストナイト系晶析型脱リン材におけるリン除去メカニズムに関する研究

Abstract

Wollastonite consolidated by carbonation is one of promising materials as a crystallization-type phosphorous adsorbent. The detailed crystallization mechanism of phosphorous, however, has not been clarified yet. In this study, the crystallization of calcium phosphate on the surface of the consolidated body of wollastonite was examined in detail by SEM, EDX and XRD in order to clarify the detailed mechanism of phosphorous removal by crystallization.It was found that the crystallization of calcium phosphate occurred to a depth of 100μm from the surface of the wollastonite consolidated body, which was the region fully carbonated and mainly composed SiO2 gel-like compound and CaCO3 (calcite and aragonite). Further investigation of crystallization of calcium phosphate using SiO2 gel and CaCO3 powders consolidated by gypsum revealed that a crystallization site of calcium phosphate was probably the surface of CaCO3 crystals generated by the carbonation of wollastonite. Moreover, it was found from the investigation using calcite and aragonite single crystals that the crystallization of calcium phosphate occurred on the surfaces of both crystals and that the surface of aragonite was slightly advantageous for crystallization. XRD analysis showed that Ca-deficient hydroxylapatite (Ca9(HPO4)(PO4)5OH, d-HAP) and dicalcium phosphate dehydrate (CaHPO4·2H2O, DCPD) were mainly crystallized on the surfaces of aragonite and calcite, respectively.