Properties of glass-ceramics prepared from Kira (waste by-products of silica sand and kaolin clay refining) and various additives

Five different glass-ceramics were prepared from Kira (waste by-products from processing of silica sand and kaolin clay) with various additives. Mixtures of Kira with CaCO₃ (mass ratio 62.7/37.3, designated sample CC), dolomite (mass ratio 65/35, CM1) and mass ratio 75/25 (CM2), and paper sludge ash waste (mass ratio 55/45, PS) were melted at 1350-1400°C, quenched in water and ground to <48 mesh. Glass-ceramic samples were prepared by re-firing these powders at 950-1100°C. The main crystalline phases formed were wollastonite in CC, diopside (in CM1), anorthite (in CM2), quartz solid solution (in PS fired at 1000°C, designated PS1) and cristobalite (in PS fired at 1100°C, designated PS2). All these glass-ceramics showed a smooth-textured shiny white appearance and had very good mechanical properties; their four point bending strengths ranged from 63 to 130 MPa and Vickers microhardness values ranged from 6.0 to 7.6 GPa. Their thermal expansion coefficients ranged from 4.7×10^-6 to 8.1×10^-6 /°C and their chemical durabilities towards acid (1 mass% H ₂SO₄ at 90°C) were in the range 3.6×10 ^-9 to 93×10^-9 g/(cm²s). Their resistance to alkali (1 mass% NaOH at 90°C) ranged from 8.2×10^-9 to 27×10^-9 g/(cm²s). The chemical durability of these glass-ceramics is better than that in commercial glass-ceramics used as building materials. Kira waste is therefore a promising candidate raw material for glass-ceramic building materials, ceramic tiles, etc.