Thermodynamics of chromite ore oxidative roasting process.

To explicate the thermodynamics of the chromite ore lime-free roasting process, the thermodynamics of reactions involved in this process was calculated and the phrases of sinter with different roasting times were studied. The thermodynamics calculation shows that all the standard Gibbs free energy changes of the reactions to form NaCrO, NaO·FeO, NaO·AlO and NaO·SiO via chromite ore and NaCO are negative, and the standard Gibbs free energy changes of the reactions between MgO, FeO and SiO released from chromite spinel to form MgO·FeO and MgO·SiO are also negative at the oxidative roasting temperatures (1 173-1 473 K). The phrase analysis of the sinter in lime-free roasting process shows that NaO·FeO, NaO·AlO and NaO·SiO can be formed in the first 20 min, but they decrease in contents and finally disappear with the increase of roasting time. The final phase compositions of the sinter are NaCrO, MgO·FeO, MgO·SiO and MgO. The results indicate that NaCrO can be formed easily via the reaction of NaCO with chromite ore. NaO·FeO, NaO·AlO and NaO·SiO can be formed as intermediate compounds in the roasting process and they can further react with chromite ore to form NaCrO. MgO released from chromite ore may react with iron oxides and silicon oxide to form stable compounds of MgO·FeO and MgO·SiO, respectively. [ABSTRACT FROM AUTHOR]