Inhibition of Cr6+ in calcium aluminate cement bonded refractory castables using chrome-hibonite, Ca(Al,Cr)12O19 raw materials

The addition of Cr3+-oxides in a refractory provides unmatched corrosion resistance at high temperatures but generates toxic and water-soluble Cr6+ compounds, particularly in oxygen-rich and alkaline conditions. In this paper, a Cr3+ raw material (chrome-hibonite) was synthesized by the solid oxide reaction route and was used to make different calcium aluminate cement bonded alumina-based refractory castables. The castables (chrome-free and Cr3+ oxides containing) were compared regarding corrosion resistance against municipal waste slag at 1500 °C under air atmosphere. The relative Cr6+ formation within the castables containing Cr3+ oxides (Cr2O3 and Ca(Al,Cr)12O19) upon heat treatment at 500–1500 °C were investigated using X-ray diffraction (XRD), and Cr6+ leaching test, etc. Compared to castables without Cr3+ oxides, the corrosion resistance increases at least 5 times upon Cr3+-oxides addition, irrespective of their forms (Cr2O3 or Ca(Al,Cr)12O19). However, at all the tested temperatures, Ca(Al,Cr)12O19 addition into the castables could suppress the Cr6+ generation significantly (below the standard solid-waste disposal limit of 3 mg/L) compared to Cr2O3, which was well above the limit.