Effect of Na2CO3 and CaCO3 on deep dephosphorization by the direct reduction of high-phosphorus oolitic hematite

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Abstract
The direct reduction–magnetic separation process based on coal is considered to be one of the most important methods that can effectively utilize high-phosphorus oolitic hematite. In this study, the mechanism of the effects of CaCO3 and Na2CO3 on the dephosphorization of high-phosphorus oolitic hematite during the direct reduction process was investigated using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The results showed that Na2CO3 and CaCO3 reacted with Al2O3 and SiO2 during the direct reduction process, inhibited the generation of hercunite (FeAl2O4) and fayalite (Fe2SiO4), and promoted the reduction of metallic iron (Fe). Furthermore, the reaction inhibited the reduction of apatite and prevented the generation of FeP2. Na2CO3 could change the form of phosphorus in the gangue from Ca3(PO4)2 to Na2Ca4(PO4)2SiO4. Increasing the dosages of Na2CO3 and CaCO3 in the dephosphorization agent and increasing the content of Na2CO3 in the dephosphorization agent were beneficial to the growth of metallic iron particles, and increasing the dosage of Na2CO3, CaCO3 in the dephosphorization agent had more significant effects on metallic iron particles than increasing the content of Na2CO3 in the dephosphorization agent. The research conducted in this study is expected to provide a basis for the effective exploitation of complex and refractory iron ores.

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