Features of joint lime autoclave desiliconization of quartz-titanium concentrates and hydrothermal synthesis of calcium hydrosilicates

The Baikov Institute of Metallurgy and Materials Science of the Russian Academy of Sciences (IMET RAS) developed an autoclave lime-alkali desiliconization method for titanium concentrates from the Pyzhemskoye and Yaregskoye deposits (Sredny and Yuzhny Timan, Komi Republic). The ores of these deposits are quartz-leucoxene and quartz-ilmenite-leucoxene sandstones. The formation of the titanium component of these deposits is associated with the leucoxenization of ilmenite. The geological process involved the removal of iron from the parent titanium minerals and the filling of the resulting voids with quartz through its crystallization from hydrothermal solutions. This resulted in the ultra-dispersed size of inclusions (1 – 20 µm) of SiO 2 and its structure characterized by weaker (unsaturated) Si – O (Si) bonds. As a result, a high degree of desiliconization of leucoxene and ilmenite concentrates is achieved at 220 °C under autoclave conditions due to the almost complete removal of quartz from titanium grains. At the same time, hydrothermal synthesis of calcium metasilicate hydrates (tobermarite, xonotlite) takes place, the morphological properties of which depend on the conditions of autoclave leaching. In the autoclave, during a relatively short duration of the process, at a ratio of CaO/SiO 2 = 0.7 – 1.0, calcium silicate with a needle-like habit is obtained, which forms predominantly radially radiant sinters. Upon subsequent calcination, their complete dehydration occurs with the crystallization of β-wollastonite (CaSiO 3 ) increasingly gaining practical application in various fields, including science-intensive ones.