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

Abstract Highly corrosion resistant Cr 2 O 3 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 Cr 2 O 3 based castables were prepared by varying the Cr 2 O 3 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, CaCrO 4 formed at 500–700 °C, while Ca 4 Al 6 CrO 16 formed in the intermediate temperature regime (900–1300 °C). The Cr(III) containing (Al,Cr) 2 O 3 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).