Behavior of Calcium Compounds under Hydrothermal Conditions during Alkaline Leaching of Aluminosilicates with the Synthesis of Fillers for Composites

Abstract

Calcium oxide plays an important role in alumina production by binding SiO2 from aluminosilicate raw materials (bauxite, nepheline, kaolinite, etc.) in aluminum-free compounds. The efficiency of the hydrochemical technology depends on the activities of calcium oxide or its compounds introduced into the alkaline aluminosilicate slurry. In this paper, we considered the effects of different calcium compounds (calcium carbonate CaCO3, gypsum CaSO4·H2O, calcium oxide CaO and calcium hydroxide Ca(OH)2), introduced during the hydrothermal stripping of aluminosilicates with alkaline solutions, on the degree of aluminum oxide extraction, with the subsequent production of fillers for composites. Ca(OH)2 was obtained by the CaO quenching method. Extraction of Al2O3 in an alkaline solution was only possible with Ca(OH)2, and the degree of extraction depended on the conditions used for CaO quenching. The effects of temperature and of the duration of CaO quenching on particle size were investigated. In potassium solution, the best results for Al2O3 extraction were obtained using CaSO4·H2O gypsum. The obtained solutions were processed using the crystallization method.