Phosphorus Reaction Characteristics In Reduction Of High Phosphorus Oolitic Hematite Ore

High phosphorus oolitic hematite ore is a kind of typical refractory iron ore, which is characterized by high content of rion and phosphorus, fine dissemination and complex mineral compositions. Therefore, it is faced with a grand challenge for the current beneficiation technology in China to handle it effectively in practice. Recently, a better iron separation index of iron product has been gained by coal-based reduction, while the problem of phosphorus in question still has not been properly solved. Based on the document literature published, current study of phosphorus is restricted to the process selection and parameter optimization. Unfortunately, the relevant theoretical research and mechnism analysis are severely lacking, especially being scarce on reaction characteristics of phosphate and phosphorus migration behaviour in the coal-based reduction process, which is just the research purpose of this topic.In this paper, process mineralogy characteristics of high phosphorus oolitic hematite ore was researched in detail. Process mineralogy characteristics of high phosphorus oolitic hematite ore showed that the total iron grade was 42.21%, mainly existing in the form of hematite, while the content of phosphorus was as high as 1.31%, and the phosphorus mainly existed in collophane with the formation of apatite. Majority of the gangue minerals were quartz and oolite chlorite. What’s worse, the iron minerals were tightly embedded with oolite chlorite, collophane, quartz and clay minerals into circular oolitic particles, which were difficult to be destroyed, causing much harder to gain better degree of liberation. Therefore, the traditional processing methods are impossble to implement the effective enrichment of iron. So, reasonable joint mineral smelting and processing technology should be adopted to handle it, namely coal-based reduction process, which is supposed to realize the comprehensive utilization of high phosphorus oolitic hematite ore in practice.On this basis, we systematically examined the effects of reduction temperature, reduction time and C/O molo ratio on rcoal-based reduction. According to the separation indexes of iron and phosphorus in reduced products, the optimum reduction conditions of coal-based reduction were determined as follows:reduction temperature of 1250℃, reduction time of 50 min, and C/O mole ratio of 2.0. Characteristics of the reduced product indicated that high phosphorus oolitic hematite are had been reduced to metallic iron, and grew as the iron particles after coal-based reduction. Moreover, these iron grains were well developed with smooth surface, and most of the phosphorus had migrated into the iron. At the same time, the iron particles had already produced a good separation with tailings, which laid a solid foundation for the subsequent operation.From the macro, distribution of phosphorus among phases was clarified as well as the preferential migration pathway of phosphorus firstly. Under the optimum conditions of coal-based reduction, the tendency of phosphorus enrichment sequence in three phases was metallic phase, slag phase and gas phase successively. In any case, the phosphorus in gas phase was always the lowest. The migration phenomenon of phosphorus existed only from slag phase to metallic phase, and the slag phase had limited ability to store phosphorus. Once reaching the saturation condition, the slag phase would no longer have the ability to store phosphorus, and the phosphorus would have to evaporate into the air before the iron was reduced completely.And then, real coal-based reduction experiments with artificial mixed minerals were carried out, which aimed to illuminated the reduction characteristics and evolvement behaviou of phosphate minerals from the microscopic view. This paper was supposed to provide theoretical basis for further research and comprehensive utilization of high phosphorus oolitic hematite ore. After systematically studying the reaction characteristics of phosphate minerals, the facts indicated that a large proportion of apatite was reduced to tricalcium phosphate by dehalogenation reaction under the action of SiO2, and the remaining hydroxyapatite,could not be resduced, directly entered into the slag phase. Then, under the joint action of C and SiO2, tricalcium phosphate was reduced to P2 or P4. After that, phosphorus began to gradually enter into the metallic phase, and a small part of phosphorus gas directly evaporated into the air. Some of the phosphorus gas migrated into the slag phase, and formed 3CaO·P2O5 with CaO in the slag after being oxidized by oxidizing atmosphere. And then,2CaO·SiO2-3CaO·P2O5 solid solution was generated together with the 2CaO·SiO2 and 3CaO·P2O5. After the complete formation of metallic iron, the phosphorus in 2CaO·SiO2-3CaO·P2O5 was reduced again and migrated into the iron phase. Finally, iron phosphorus compounds such as FeP and Fe2P were formed in the iron phase.In this paper, reaction characteristics of high phosphorus oolitic hematite ore by coal-based reduction were systematically researched. The topic pointed out the appropriate reduction conditions of coal-based reduction and revealed the reduction characteristics and phase structure evolution behaviour of phosphate minerals during coal-based reduction. The results laid a theoretical basis for the migration control research of phosphorus, and provided more data for further research and comprehensive utilization of high phosphorus oolitic hematite ore.