铬铁矿焙烧后期铬再氧化机理

Re-oxidation mechanism of chromite roasting in late stages

针对铬铁矿氧化焙烧后期铬转化速率降低问题，以铬铁矿焙烧过程铬转化率70%的铬渣为原料，分析铬渣的物相和化学成分，深入研究铬渣焙烧过程中温度、时间、Na2CO3和CaCO3等对铬渣中铬转化率的影响，探讨提高铬铁矿氧化焙烧后期铬转化率的机理。结果表明：铬渣主相为MgCr0.4Fe1.6O4尖晶石，副相为NaSiAlO4和Mg1.5Na9Si12Al12O48等钠硅酸盐、硅铝酸盐相；在与 Na2CO3进行氧化焙烧反应过程中铬转化率仅为50%~60%，钠硅酸盐、硅铝酸盐等相的存在导致Na＋的利用率降低，造成铬渣中的铬转化困难；Ca的引入置换了铬渣中副相的Na，铬转化率提高到84.7%，生成了高熔点的Ca2Fe1.2Mg0.4Si0.4O5硅酸钙盐等相，增大了焙烧过程中Na＋浓度，促进了铬的转化，提高了焙烧后期铬的转化率。

Based on the conversion rate of trivalent chromium at the late stages of the chromite lime-free roasting, Na2CO3 roasting of the chromium residues obtained by roasting the chromite ore with Na2CO3 with the conversion rate of 70% was used as raw materials. The phases and chemical composition of chromium residues were analyzed firstly, the effects of roasting process conditions such as roasting time, roasting temperature and the amount of Na2CO3 and CaCO3 addition, on the Cr conversion rate were further investigated. The mechanism of reoxidation of trivalent chromium at the late stages of roasting process was studied. The results show that the main phase of the chromium residues is MgCr0.4Fe1.6O4 spinel, and some sodium silicate and silicon aluminate phases, such as NaSiAlO4 and Mg1.5Na9Si12Al12O48 also exist in the chromium residues. During the roasting process of chromium residues reacting with Na2CO3, the conversion rate of trivalent chromium of chromium residues is only 50%？60%, due to low utilization of Na＋ that resulted from the formation of sodium silicate and sodium silicon aluminate phases. The conversion rate of trivalent chromium increases to 84.7% when the CaCO3 is added into the roasting process of chromium residues, the sodium silicate and silicon aluminate reacts with Ca to generate high melting point calcium silicate salt phases, such as Ca2Fe1.2Mg0.4Si0.4O5. Therefore, the concentration of Na＋ is improved and the chromium transformation is promoted, and the conversion rate of trivalent chromium increases at the late stages of roasting process.