Preparation of Nepheline-Based Ceramic Foams from Basalt Tailing and Black Cotton Soil

A type of ultra-light weighted, low-thermally conductive but mechanically strong ceramic foams (CF) were fabricated via the direct foaming method of using basalt tailings (BT) and black cotton soil (BCS) as main components. The sodium hydroxide (NaOH) dissolved in water glass (Na 2 SiO 3 ) and calcium carbonate (CaCO 3 ) were used as fluxing and foaming agents, respectively. The product was demonstrated to have excellent strength-to-density properties (compressive strength > 1.82 MPa, density < 0.57 g/cm 3 ) and a low thermal conductivity (0.057 W/m·K), which meets standards of ASTM C552-14 (Grade 24) or GB/T33500-2017 (Grade L). Factors that affect the physicochemical (bulk density, apparent density, and water absorption) and mechanical properties were investigated, which include dosages of BT, NaOH, and CaCO 3 . Optimum parameters were found as sintering temperature 850 °C, reaction time 45 min, and dosage of BT/(BT + BCS) = 70% wt., NaOH = 13% wt. versus the total weight of BT and BCS (w(BT + BCS)), and foaming agent CaCO 3  = 0.1% wt. versus w(BT + BCS). The crystalline phase in the foamed ceramics was confirmed as nepheline which was produced by desilication of orthoclase or plagioclase with presence of NaOH. This direct foaming method of using the BT + BCS system was proven to be an efficient way to prepare foamed ceramics.