On the reaction between magnesiochromite and calcium oxide

The role of temperature on Cr(VI) formation and reduction during heating of chromium-containing sludge in the presence of CaO

“…The reduction from CaCrO 4 to Ca(CrO 2 ) 2 implies CaCrO 4 is thermodynamically less stable at higher 1000°C, and there is always the trend of CaCrO 4 transforming into more stable phase. MgCr 2 O 4 with a high melting point (2330°C) performs inert at high temperature, which indicates it is thermodynamically more stable than CaCrO 4 (Klyucharov and Eger, 1963). Moreover, in prior studies (Barbu et al, 2012El-Sheikh and Rabah, 2013), the decomposition of MgCrO 4 into MgCr 2 O 4 occurs at about 500°C, far lower than that for the transformation of CaCrO 4 into Ca(CrO 2 ) 2 , which further suggests the presence of Mg might induce Cr(VI) to be reduced into Cr(III) at lower temperature.…”

High-Temperature Chemical Stability of Cr(III) Oxide Refractories in the Presence of Calcium Aluminate Cement

“…However, these oxide additives usually result in low melting point phases in the matrix, deteriorating either the thermo-mechanical properties or the slag corrosion resistance [ 23 , 24 ]. Previous research indicated that incorporating chromium into solid solution phases can reduce the risk of Cr(VI) formation in the Cr 2 O 3 -containing materials [ 25 , 26 , 27 ]. For example, the investigation of the Al 2 O 3 -Cr 2 O 3 -CaO-MgO pure system confirmed that composite spinel Mg(Al,Cr) 2 O 4 could co-exist with CA 2 , where chromium existed in +3 state [ 25 , 27 ].…”

“…Previous research indicated that incorporating chromium into solid solution phases can reduce the risk of Cr(VI) formation in the Cr 2 O 3 -containing materials [ 25 , 26 , 27 ]. For example, the investigation of the Al 2 O 3 -Cr 2 O 3 -CaO-MgO pure system confirmed that composite spinel Mg(Al,Cr) 2 O 4 could co-exist with CA 2 , where chromium existed in +3 state [ 25 , 27 ]. Again, Wu et al [ 28 ] studied the effect of temperature on Cr(VI) formation in a pure (Al,Cr) 2 O 3 system with CAC in air atmosphere, where (Al 1−x Cr x ) 2 O 3 was found to be chemically stable against CAC up to 1100 °C, beyond which Ca 4 Al 6 CrO 16 (hauyne) phase predominantly start from.…”