Synthesis of sodium silicate from the acid leached calcined kaolinitic clay residue of aluminum sulfate industry

Abstract

Abstract Acid leached calcined kaolinitic clay (ALCKC) is a residue of aluminum sulfate coagulant manufacturing process; it is a solid acidic waste that is harmful to environment. Silica dissolution process was systematically studied, including the thermodynamic analysis and the influence of aluminum content on the leaching of amorphous silica. Simulation studies have shown that aluminum combine with silicon to form silica–alumina gel, and zeolite, thereby preventing the leaching of silica. Maximizing the removal of aluminum, iron and titanium can effectively improve the leaching of silica in the subsequent process, and corresponding element removal rates are 45%, 41% and 15%, respectively. The removed aluminum is reused to prepare PAC. The silica extraction rate reached 88% at a conditions of (NaOH; 20%, NaOH to ALCKC; (v/ w) 5, 75°C, 2h), and sodium silicate modulus (nSiO2:nNa2O) is 1.1. The results indicated that a large amount of silica was existed in amorphous form. Precipitated silica was obtained by acidifying sodium silicate solution at a pH 7.0 using sulphuric acid. The prepared sodium silicate (1.1) was used for further synthesis of sodium silicate with nSiO2:nNa2O = more than 3