Phase transformation of glass-ceramics produced by naturally cooled yellow phosphorus slag during calcination

Naturally cooled phosphorus slag is formed during the production of phosphorus, which contributes to a serious environmental pollution. The crystallization kinetics has already been evaluated in previously published studies during the process of CaOAl2O3SiO2(CAS) glass-ceramics preparation from naturally cooling phosphorus slag. This study was focused on calculating the thermodynamic equilibrium phases of Ca, Al and Si using FactSage6.4 thermodynamic software package at different temperatures. X-ray diffraction, Fourier transform infrared spectroscopy and Scanning electron microscopy were employed to examine the phase status of Ca, Al and Si elements. The results showed that phase transformation started at 450 °C and formation of liquid slag phase occurred at 950 °C in naturally cooled yellow phosphorus slag heated to molten state. The calcium-containing phase had changed to CaO(slag) and Ca3(PO4)2 at high temperatures. Also, aluminum-containing components present in liquid Al2O3 slag phase formed at 1000 °C and silica-containing phase at high temperatures were dominated by SiO2, CaSiO3, and SiO2(slag). Finally, SiO2 and further migration to molten SiO2(slag) were noticed as the temperature rose.