The potential usage of waste foundry sand from investment casting in refractory industry

Application of waste foundry sand (WFS) obtained from investment casting in refractories is a promising alternative developed in recent years for reducing waste landfill while also producing high-value products. It is important to enlarge the applicable area in a refractory, especially with the increasing generation of WFS and growing tension in global mineral supply. Systematic studies on as-received WFS and its microstructure evolution after thermal treatment are rare; this imposes restrictions on using WFS in various applications. In this study, WFS is systematically analyzed, and the microstructure evolution of WFS specimens with thermal treatment at 1300-1550 degrees C is investigated. Quantitative analysis of the crystal phases indicates that WFS contains 46.2 wt% mullite, 28.1 wt% cristobalite, and 10.9 wt% zircon; the main oxidation states of Fe and Ti in WFS are Fe3O4 and TiO2. Leaching of WFS is hazardous; Thermal treatment below 1500 degrees C is harmless. The transformation of tetragonal ZrO2 to monoclinic ZrO2 in the specimens sintered at 1500 degrees C reduces the cold modulus of rupture, and Fe2O3 decomposition at 1550 C reduces the bulk density and modulus of elasticity. Phase changes significantly affect the true density and melting of cristobalite at 1550 degrees C causes a sharp decrease in density. (C) 2018 Elsevier Ltd. All rights reserved.