Effect of sodium aluminate on chromium spinels oxidation in chromite lime-free roasting process
(School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: The reaction between Na2O·Al2O3 and chromium spinels or chromite in the roasting process was systemically investigated to reveal the effects of Na2O·Al2O3 on chromium oxidation. The results of Na2O·Al2O3 roasted with MgO·Cr2O3 illustrate that only about 50% of the chromium in MgO·Cr2O3 can convert into Na2CrO4, while the remaining chromium converts into an Al-bearing spinel Mg(CrAl)O4. Mg(CrAl)O4 is found to be difficult to further react with Na2O·Al2O3. The oxidative roasting of Na2O·Al2O3 with chromite further confirms that Na2O·Al2O3 cannot fully react with some chromium spinels, which reveals the cause of the low chromium oxidation rate in the traditional chromite lime-free roasting process. Based on the experiment results, a strategy for eliminating the impacts of Na2O·Al2O3 in the lime-free roasting process was proposed, in which adding more Na2CO3 for forming Na2O·Al2O3 is considered. The chromium oxidation rate can rise close to 100% with the new strategy. This study contributes to better understanding the chromite lime-free roasting process and provides a new idea for developing the chromate salts manufacturing process more efficiently and cleanly.
Key words: chromate; sodium aluminate; chromite; chromium spinel; oxidative roasting