Desilication and Recycling of Alkali-Silicate Solution for Low-Grade High-Silica Bauxite Utilization

Abstract

This study investigated the effects of CaO addition amount, initial caustic and silica concentrations, and reaction temperature on the desilication ratio in an alkali-silicate solution. The optimal desilication conditions for an alkali-silicate solution with active CaO were obtained: caustic solution concentration, 100–110 g/L; initial SiO2 concentration, 7–9 g/L; Ca/Si molar ratio, 1.2; reaction temperature, 368 K; reaction time, 2 h; stirring rate, 300 rpm. The kinetics of the desilication results indicated that the reaction matched the shrinking core model of a liquid–solid multiphase reaction, wherein the apparent activation energy was 29.35 kJ/mol and the control step was solid film diffusion. Ca(OH)2 formed a film on the particle surface, impeding further desilication. After five cycles of desilication, the aluminum-to-silicon ratio (A/S) of the bauxite concentrate was > 7 and that of roasted bauxite was 4.01.