Thermal activation and alkali dissolution of silicon from illite

Abstract TGA, DTA, FTIR, XRD and 29Si MAS NMR were used to investigate the thermal activation of illite. Illite experiences a series of thermal solid-state phase transformations. Dehydroxylation at 400∼700 °C forms dehydrated illite, which remains the layered framework of illite. From 700 °C to 1093 °C, Si–O tetrahedral framework remains unchanged. When heated above 1093 °C, the layered structure is destroyed and an amorphous silica-rich glass phase is formed. The mullitization occurs when the temperature exceeds 1100 °C. XRD and FTIR studies show that the silica in silica-rich glass phase dissolves in soda liquor, which indicates that silicon can be removed from illite after thermochemical activation (TCA) followed by alkali leaching. The formation of sodium aluminosilicates of Na 96 Al 96 Si 96 O 384 and 0.95Na 2 O · Al 2 O 3 · 3.25SiO 2 · 4.79H 2 O during alkali leaching may reduce the desilication to a great extent. Desilication tests after TCA show that the suitable activation conditions for illite are 1100∼1150°C and 90∼60 min. A desilication of 45% was obtained under the conditions for an ore sample bearing about 85% illite, 9% quartz and 5% muscovite.