Inhibited Cr(VI) formation in Cr2O3-containing refractory castable using reactive MgO as hydraulic binder

Reactive MgO was used in the first time as alternative hydraulic binder of calcium aluminate cement (CAC) to prepare Cr2O3-bearing refractory castable. The formation of Cr(VI), and physical and mechanical properties of MgO-bonded refractory castables after heat-treating were investigated. Microstructural characterization and phase composition analyses on the heat-treated MgO-bonded refractory castable matrices resulted in a comprehensive understanding of the mechanism for the inhibition of Cr(VI), and of the strength development during firing. The results indicate that compared with CAC, Cr(VI) levels were 6.7-28.1 times lower using reactive MgO after firing at 700-1300 degrees C. The in situ Mg(Cr,Al)2O4 spinel formed from the preferential interactions among MgO and Cr2O3 and Al2O3 would be the main reason leading to the inhibited Cr(VI) formation and strength development during firing.