Phase evolution with temperature in chromium-containing refractory castables used for waste melting furnaces and Cr(VI) leachability

Abstract

Highly corrosion resistant Cr2O3 based refractory linings are required for waste melting furnaces due to the complex melting environment. However, these linings are susceptible to Cr(VI) generation during service. In this study Cr2O3 based castables were prepared by varying the Cr2O3 content (4, 8 & 12 wt%) and heated in the temperature range of 500–1500 °C in the air atmosphere to simulate the service conditions. The formations of various phases were studied using XRD and SEM-EDS. The Cr(VI)-containing phase, CaCrO4 formed at 500–700 °C, while Ca4Al6CrO16 formed in the intermediate temperature regime (900–1300 °C). The Cr(III) containing (Al,Cr)2O3 solid solution phase started to form at 1100 °C which predominantly formed at 1500 °C. The oxidation states of chromium in solid state transferred in the order Cr(III)→Cr(VI)→Cr(III) with the increase in temperature. The specimens treated at 500–1300 °C contain ~ 474–5646 mg/kg of Cr(VI) whereas specimens at 1500 °C exhibit only ~ 63–69 mg/kg of Cr(VI).