Preparation Of Iron Carbide From High Phosphorus Oolitic Hematite And The Dephosphorization Of Product

High phosphorus oolitic hematite is an important sedimentary iron ore in China,with the total reserves of around 3.72 billion ton.Because of the too fine mineral crystallization grain size and complex composition,ore dressing and dephosphorization treatment is extremely difficult.So far the high phosphorus oolitic hematite reserves have remained largely unexploited.Meanwhile,iron carbide,can be an excellent replacement of scrap,has been concerned widely for its unique physical and chemical propertie as well as production conditions.In this paper,high phosphorus oolitic hematite powder was used as raw material,reacted with the H₂/CH₄ to prepare iron carbide in the temperature range from 873 K¹073 K,the effects of temperature and mineral powder particle size on the iron carbide formation and establishment of dynamic model were investigated.A certain quantity of iron carbide had been prepared from high phosphorus oolitic hematite at the the optimum temperature and mineral powder particle size.Iron carbide prepared from high phosphorus oolitic heamtite was treated by ball milling and subsequently magnetic separation.The effects of ball milling time and ball-to-powder mass ratio on the magnetic separation of iron carbide products were studied.The conclusions are as follows:?1?Considering the systems of Ca3?PO4?2-SiO2 and Ca3?PO4?2-SiO2-Al2O3,thermodynamic calculations of the phosphorus behavior with the H₂ and CH₄ were conducted by defining the relative partial pressure of phosphorus-bearing gas phase?P/0= 0.001?.Results show that P2 is the most prone P-bearing gas with the reaction temperature of higher than 1599 K,and the solid product should be CaSiO3 or Ca Al2Si2O8.?2?Hematite in the high phosphorus oolitic hematite mostly appears as oolitic granular distribution.Quartz crystalline particles are bulky and have obvious boundary with hematite.Apatite is very fine disseminated and appears as concentric circles in the ooids.Chlorite mainly fills in hematite microcrystalline,and the structure of the chlorite combined with hematite is more complicated.?3?From 923 K to 1073 K,iron carbide can be successfully prepared from high phosphorus oolitic hematite,by H₂ for the reduction firstly,and subsequently using CH₄ for the progress of the carburization.The average particle size of iron carbide is 2.5 ?m.When the temperature is lower than 923 K,the reduction of high phosphorus oolitic hematite can happen,but the ore cannot be carburized.?4?During the preparation of the iron carbide from high phosphorus oolitic hematite,the reduction and carburization rate increases with the temperature increase.However,the reduction rate and the carburization rate will not increase obviously with the temperature of higher than 1023 K.Comprehensively,the best temperature of the iron carbide preparation from high phosphorus oolitic hematite is 1023 K,and the influence of temperature is much more important than that of mineral powder particle size.?5?The kinetic experiments indicates that the optimum particle size of the high phosphorus oolitic hematite in the preparation of iron carbide from high phosphorus oolitic hematite is 120 160 mesh.The calculation of the kinetic model illustrates that the reaction activation energy of high phosphorus oolitic hematite with the mineral powder particle size in 120¹60 mesh is lowest.The reduction reaction activation energy is 44.95 kJ?mol-1.?6?With the elongation of ball milling time from 2h to 6h,the average particle size is decreased from 6.48?m to 5.23 ?m,at the ball-to-powder weight ratio of 15:1.With ball-to-powder weight ratio increasing from 10:1 to 20:1,the average particle size is decreased from 6.01 ?m to 4.40 ?m under the condition of the ball mill time of 6h.In Fe-P separation experiments by the method of ball mill magnetic separation,the highest dephosphorization rate of 81.33% can be obtained,at the ball grinding time of 6 h and ball material ratio of 15:1,but only 19.33% iron carbide can be recovered.Comprehensive consideration,the ball mill magnetic separation cannot work well,and it is difficult to achieve a very good Fe-P separation effect by only physical separation.