Surface dissolution of calcium phosphate glass ceramics in dilute acid conditions

Calcium phosphate glass–ceramic materials in the P2O5–CaO–SiO2–K2O system were prepared from mineral and industrial waste raw materials. They were characterized by chemical analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tricalcium phosphate (α and β-Ca3(PO4)2), tetracalcium phosphate (Ca4P2O9) and glassy phases were identified in various proportions. The materials were treated in water, ammonium citrate, ammonium acetate and citric acid solutions. The mechanism of attack of the different phosphate phases in dilute acid conditions was established mainly following the P, Si, Ca, K concentrations versus time by inductively coupled plasma optical emission spectroscopy (ICP–OES). The results show that these glass–ceramic materials can be used as controlled released fertilisers.