2018 Volume 58 Issue 10 Pages 1768-1774
Recently, additives such as CaCO3 and Na2CO3 have been proven to be capable of enhancing the reduction of high-phosphorus oolitic hematite ore and obtaining high-grade direct reduction iron (DRI) with low-P by magnetic separation. In this study, the mechanisms of adding CaCO3 during direct reduction were further studied by gas analyzer, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that CaCO3 can inhibit the reduction of fluorapatite, and more P still remained as fluorapatite which can be removed by magnetic separation. In addition, CaO and CO2 decomposed from CaCO3 promoted reduction atmosphere, but the contribution of CO2 to reduction of iron oxides was very limited, in fact CaO played a central role. An appropriate CaCO3 dosage can enhance reduction of oolitic hematite. Addition of CaCO3 led to the consumption of quartz and inhibited the generation of fayalite, which reduced FeO content in the slag, and as a result more FeO was reduced to metallic iron. A DRI with 94.51 mass% Fe, and 0.17 mass% P can be obtained at a iron recovery of 89.3 mass% by adding 10 mass% CaCO3. However, excessive CaCO3 reacted with gangue and FeO to generate a large amount of slag (such as kirschsteinite), which hindered the diffusion and growth of the iron grain and increased the iron loss.