Formation and leachability of hexavalent chromium in the Al2O3-CaO-MgO-Cr2O3 system

The Al2O3-CaO-MgO-Cr2O3 system has immense potential for refractory castables applications. However, Cr(III) can potentially be oxidized to carcinogenic Cr(VI) during the usage, which can cause subsequent problems with disposal. Equilibrium experiments on the Al2O3-CaO-MgO-4wt%Cr2O3 system were performed at 1500 degrees C in air. The effect of MgO addition (0 and 20 wt%) on the formation and leachability of hexavalent chromium was investigated using XPS, XRD, SEM-EDS, the TRGS 613 standard Cr(VI) leaching test and multiple leaching tests. A Cr(VI)-containing phase Ca4Al6CrO16 predominantly formed in the samples with 0 and 5 wt% MgO, while the Cr(lll)-containing Mg(Al, Cr)(2)O-4 spinel phase formed in the samples with 10 and 20 wt% MgO. Addition of MgO suppressed the formation of Cr(VI) while favored the formation of spinel phase. Concentrations of Cr(VI) in the leachates from TRGS 613 tests exceeded the European limit of 0.0002 wt% in all samples, although decreased significantly with 20 wt% MgO addition.