Thermal activation and alkali dissolution of silicon from illite

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 similar to 700 degrees C forms dehydrated illite, which remains the layered framework of illite. From 700 degrees C to 1093 degrees C, Si-O tetrahedral framework remains unchanged. When heated above 1093 degrees C, the layered structure is destroyed and an amorphous silica-rich glass phase is formed. The mullitization occurs when the temperature exceeds 1100 degrees 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 Na96Al96Si96O384 and 0.95Na(2)O center dot Al2O3 center dot 3.25SiO(2)center dot 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 similar to 1150 degrees C and 90 similar to 60 min. A desilication of 45% was obtained under the conditions for an ore sample bearing about 85% illite, 9% quartz and 5% muscovite. (C) 2007 Elsevier B.V. All rights reserved.