Hydrothermal formation mechanism of the efficient desilication product hydroandradite (3CaO·Fe2O3·xSiO2·(6-2x)H2O)

Abstract

As a theoretically ideal and efficient desilication product without Na2O and Al2O3, the formation behavior of hydroandradite under different hydrothermal conditions by adding synthetic sodium ferrite was systematically investigated by adding synthetic sodium ferrite. Thermodynamic calculations indicate that increasing the reaction temperature is advantageous to promote the formation of hydroandradite, and hydroandradite with a high iron substitution coefficient is more difficult to precipitate than that with a low iron substitution coefficient. The existence of aluminate ions in solution significantly accelerates the formation of hydroandradite and shifts the characteristic peaks of the XRD spectra to the left by 0.4–0.5°/2θ. The hydroandradite in sodium aluminate solution is formed mostly by a substitution reaction from the preformed hydrogrossular and partly by spontaneous nucleation. Increasing the reaction temperature and prolonging the holding time can increase the mass fraction, silicon saturation coefficient and iron substitution coefficient of hydroandradite, while decreasing the contents of the hydrogrossular and zeolite phases