| Oolitic hematite is currently recognized as one kind of the most refractory iron ores in the worldwide. China is rich in high phosphorus oolitic hematite ore resources. There are mainly Xuanlong-type oolitic hematite in the northern China and Ningxiang-type oolitic hematite in the southern China. There has been identified4billion tons reserves of the resources, and more than10billion tons in the long-term in China. The unique structure and complex chemical composition of the oolitic hematite make it difficult to benefication and smelting. So far the oolitic hematite has not been utilized.In this study, by using X-ray diffraction analysis, X-ray fluorescence spectrum analysis, optical microscopy and scanning electron microscopy (SEM) analysis, the reduction roasting behaviors of main minerals and basic characteristics of high phosphorus oolitic hematite were investigated, technology of iron-phosphate separation was proposed by adding SSMP obtained from pretreated pageite.High phosphorus oolitic hematite raw ore sample is of low-grade iron (43.20%) and high phosphorus(0.90%), SiO2content is19.47%and7.27%of A12O3. Iron minerals are embedded with the fine particle gangue minerals and in the complex occurrence relationships with high content harmful elements of P, so it belongs to a typical refractory ore which is extremely difficult to be treated with.The reduction roasting behaviors of high phosphorus oolitic hematite are as follows:reduction roasting thermodynamic analysis of apatite shows that it is difficult for Ca5(PO4)3F, SiO2, A12O3and MgO to react with each other spontaneously and form P2in the reduction system, reduced with sodium salts, apatite transforms into Na2Ca4(PO4)2SiO4and NaCaPO4. There is no obvious change with the rising of reducing temperature. Few phosphorus volatilizes from900℃to1100℃. In Fe2O3-apatite-sodium salts system, phosphorus volatile ratio reaches10%-20%reduced from900℃to1100℃for60min. Iron trnasforms into Fe3C mainly at lower temperature (<900℃), but into metallic iron mainly at higher temperature. Na2Ca4(PO4)2SiO4and NaCaPO4are main phosphorus-bearing minerals after reduced at the temperature from900℃to1100℃.The sodium salts modified pageite can improve the iron-phosphate separation of high phosphorus oolitic hematite by reducing roasting significantly. The optimum conditions for sodium salts modified pageite (SSMP) are as follows:the dosage of Na2SO4is25%and the dosage of Na2CO3is20%, pre-reduced at900℃to950℃for30min. The optimum conditions of reduction roasting of the high phosphorus oolitic hematite in the presence of SSMP are as follows:35%dosage of SSMP, reduced at1050℃for75min, grinding fineness of reduced product95.12%undersize74μm and magnetic field intensity1000Gs. Metallic iron product with iron grade of93.29%and phosphorus content of0.08%was obtained under the optimal conditions, at the same time, the recovery of iron was88.49%, and the corresponding dephosphorization ratio was up to95.46%.Microstructure of the reduced pellet indicated that, there is phosphorus in the metallic iron particles of the roasted pellets without additives, iron and phosphate closely combined and phosphorus still exist almost in the form of apatite. With35%SSMP addition, the content of iron in the metallic iron particles reaches almost100%in the roasted pellets, there is no phosphorous in the iron particles which mainly existed in the form of metallic iron in the magnetic product after grinding-magnetic seperation. Apatite in oolitic hematite raw ore transforms into NaCaPO4. At the same time, there are reactions between SSMP and aluminum-bearing, silicon-bearing gangues during reduction roasting and form non-magnetic sodium aluminosilicate, which are easily removed by magnetic separation. It is favorable to obtain high quality metallic iron product from high phosphorus oolitic hematite by direct reduction followed magnetic separation. |
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