铬铁矿中杂质铝和铁对铬氧化率的影响及其机理

Influences of impurities of ferrous oxide and aluminum oxide on oxidation rate of trivalent chromium and its mechanism

以实验室合成的尖晶石型化合物为原料,系统地研究铬铁矿无钙焙烧体系中杂质铁和铝对Cr(Ⅲ)氧化率的影响规律及其机理。结果表明:铬铁矿中杂质铁对Cr(Ⅲ)的氧化率无明显影响;焙烧过程中FeO被氧化后得到的Fe2O3先与Na2CO3反应生成中间产物NaFeO2,它在体系中仍能起着Na2CO3的作用,使铬的氧化反应继续进行,整个Cr(Ⅲ)氧化过程的反应速率均较快;而杂质铝能明显抑制Cr(Ⅲ)的氧化,其主要原因是:在焙烧过程中,Al2O3与Cr2O3和MgO反应生成相对稳定、难溶的多元复杂氧化物MgO·(Cr2O3)0.5.(Al2O3)0.5。此外,Al2O3与Na2CO3反应生成Na2O·Al2O3,但Na2O·Al2O3很难进一步与MgO.(Cr2O3)0.5·(Al2O3)0.5反应生成Na2CrO4。

The influences of impurities of ferrous oxide and aluminum oxide on the oxidation rate of trivalent chromium and its mechanism were systematically studied using the compounds synthesized in laboratory as the starting materials in the calcium-free oxidative roasting process of chromite ore. The results show that the impurity of ferrous oxide has little effect on the oxidation rate of the trivalent chromium. Ferrous oxide is first oxidized to form ferric oxide, and NaFeO2 is formed by the preferential reaction of ferric oxide and sodium carbonate, which can further act as the alkali and thus maintain a relatively rapid oxidation rate of trivalent chromium during the whole roasting process of chromite ore. And the impurity of aluminum oxide obviously hinders the oxidation of trivalent chromium. This is mainly attributed to the formation of the complicated insoluble compound of MgO·（Cr2O3）0.5·（Al2O3）0.5. In addition, the aluminum oxide readily reacts with sodium carbonate to form sodium aluminate which is difficult to further react with MgO.（Cr2O3）0.5.（Al2O3）0.5 to form Na2CrO4, resulting in the decrease in the oxidation rate oftrivalent chromium. Key words：