Effects of Ti- and Mg-bearing minerals on hydrothermal formation of hydroandradite

Abstract

The effects of Ti- and Mg-bearing minerals on the crystal structure, morphology, particle size distribution, and formation mechanism of efficient desilication product of hydroandradite (HA) during hydrothermal conversion in a synthetic sodium aluminate solution were investigated via X-ray diffractometer, scanning electron microscope and particle size analyzer. During HA formation, anatase, rutile, and periclase dissolved in sodium aluminate solution engage in ion substitution reactions between Ti⁴⁺ and Si⁴⁺, and between Mg²⁺ and Ca²⁺, respectively. However, dissolved hydromagnesite cannot enter into the HA. The content of HA after the hydrothermal reactions changes slightly with the increase of anatase and periclase contents, but it notably decreases with increased quantities of rutile and hydromagnesite. Ti-bearing minerals reduce the particle size and enhance the specific surface area of HA, whereas Mg-bearing minerals exert the opposite effect. The morphology of HA with Ti- and Mg-bearing minerals changes from spherical particles to flocculent structure and hexagonal plate-like particles.