Fundamental Research On Iron And Phosphorus Separation Of High-phosphorus Iron Ore By Direct Reduction

High-phosphorus iron ore resources are abundant in China,and because of its high phosphorus content and complex mineral structure,it cannot be exploited.Based the coal-based direct reduction-rapid melting separation process of high-phosphorus iron,the basic research was carried out,which provided the theoretical basis for the efficient utilization of high-phosphorus iron ore.Firstly,oolitic structure and mineral reactions were in-situ observed by ore buried experiments to reveal the relationship between structure and reactions.It was found that,at the same time of fluorapatite reduced,it also diffused into iron oxide in a diffused manner,which was difficult to separate iron and phosphorus by mechanical means.Seconly,the mineral evolution and elements migration of high-phosphorus iron ore during reduction process was studied by pure material.The results showed that iron oxide was reduced to FeO firstly,than Fe-Si-Al gangue phases were formed.Fluorapatite began to decompose to Ca3(PO4)2 and CaF2.Ca3(PO4)2 and Fe-Si-Al gangue phase react rapidly to form CaAl2Si2O8 and P2.CaF2 can react with SiO2to form SiF4 gas.P element from reduction mainly distributed in ledeburite,while rarely distributed in pearlite and cementite.The distribution of phosphorus and carbon were same in iron.The process that phosphorus got into iron phase was closely related to the carburization process.P was mainly absorbed by liquid iron.With the increasing carbon content in iron phase,the metal iron melted and formed a large quantity of liquid iron which promoted the absorption of phosphorus by the iron phase.Therefore,it can be inferred that,iron phase absorbing phosphorus can be suppressed by decreasing temperature and reducing reduction agent.Thirdly,the carbothermal reduction mechanism of fluorapatite in high-phosphorus iron ore was studied.By thermodynamic analysis,it was found that it was difficult to reduce fluorapatite in the case of only carbon and fluorapatite.The Gibbs free energy by calculation showed that the reaction temperature was higher than 1400 ?;Dephosphorization of fluorapatite was promoted by Al2O3 and SiO2 to form phosphorus-containing gas.The promotion of SiO2 was stronger than that of Al2O3.Especially when Al2O3 or SiO2 was sufficient,it can cause the defluorination reaction of fluorapatite to produce tricalcium phosphate which was easier to reduce.The reduction temperature of fluorapatite was further reduced.When Fe2O3 was exist,Fe3P was formed.The formation of Fe3P and the reduction of fluorapatite mutually promote each other,which hindered the separation of iron and phosphorus.When C was sufficient,the phosphorus-containing gas was mainly P2.When C was insufficient,the phosphorus-containing gas was mainly PO.In addition,according to the results of thermodynamic analysis,the effects of Al2O3,SiO2,Fe2O3 and carbon content on the gasification of phosphorus during reduction were investigated by pure material.The complete reduction route of the fluorapatite reduction process was systematically summarized.Fourth,the distribution of phosphorus during the process of carbothermal reduction was studied by pure material to simulate high-phosphorus iron ore.The results showed that,the percentage of phosphorus in gas was higher than that in the iron at the reduction of 1100 ?.However,it was the opposite at the reduction of 1200 ?.The existence of liquid iron was the key factor to control the phosphorus absorption of iron phase.In order to achieve the separation of iron and phosphorus,the formation of liquid iron should be avoided as much as possible.The reduction temperature was 1100?,C/O=1.0 was more suitable.At this time,the phosphorus in gas was more and the phosphorus content in the metal iron was lower,which was favorable for dephosphorization of the high-phosphorus iron ore.Finally,according to the above theoretical research results,the process conditions of high-phosphorus iron ore reduction and melting were optimized.The optimized process parameters were as follows:R=1.6,reduction temperature was 1100 ?,reduction time was 30 min,C/O=1.0,the mass fraction of CaF2 and Na2CO3 were 5%.The metallization of reduced pellets was 95.31%,iron yield was 94.28%,phosphorus content in iron was 0.098%and dephosphorization ratio was 94.34%,which can meet the requirements of subsequent steelmaking.