High-temperature stability and leaching kinetics of the hexavalent chromium compound, chrome-hauyne (Ca4Al6CrO16)

Abstract Cr-refractories usually contain Cr(III) compounds that can convert into carcinogenic Cr(VI) compounds such as CaCrO4 and Ca4Al6CrO16 under alkaline and oxygen-rich conditions. Literature provides insight into the characteristics, thermal stability, and aqueous solubility of CaCrO4, while there is hardly any data available on Ca4Al6CrO16. The present paper comprehensively studied high-temperature stability and leaching kinetics and other characteristics of Ca4Al6CrO16 by using high-temperature XRD, TG-DSC, XPS, Raman, and TRGS 613. XPS confirmed that chromium in Ca4Al6CrO16 is present in the +6 oxidation state. Ca4Al6CrO16 is thermally stable up to 1500 °C in the air but decomposes in nitrogen above 1258 °C to form the Cr3+-containing phases CaCr2O4 and Ca6Al4Cr2O15. The Ksp of Ca4Al6CrO16 in deionized water is 1.0381 × 10−22, 4.5723 × 10−21 and 2.3489 × 10−20 at 12, 25, and 40 °C, respectively. The leaching process of Ca4Al6CrO16 is chemical reaction controlled, with an apparent activation energy of 58.78 kJ/mol.