Effects Of Material Status On Indexes And Iron Grain Growth During Coal-based Reduction Of Oolitic Hematite

Oolitic hematite is one of the most important refractory iron ores in the word.The ore being difficult to separate is due to the extremely fine mineral grain size and complex associated relationship,therefore the utilization rate is very low.In recent years,relevant researchers have adopted coal-based reduction followed by magnetic separation to deal with the ore and have acquired certain breakthrough in both theory and practice.Unfortunately,the relevant theoretical researches on material forms affecting coal-based reduction and iron grain growth and morphology are severely lacking.Based on the research of process mineralogy characteristics of high phosphorus oolitic hematite ore from western Hubei,under different conditions of reduction temperature,time and raw ore granularity in the paper,we systematically contrasted and analyzed the effects of different material forms including briquetting and loose ore on metallization rate,separation indexes,iron particle size and morphology after coal-based reduction.The results proved that:(1)The total iron grade was 42.21%,mainly existing in the form of hematite,Majority of the gangue minerals were quartz and oolite chlorite.What was worse,the iron minerals were tightly embedded with oolite chlorite,quartz and clay minerals into circular oolitic particles,which were difficult to be destroyed,hard to obtain a appropriate liberation.Therefore,the traditional processing methods are impossble to implement the effective enrichment of iron.So,a 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.(2)The reduction temperature,reduction time,raw ore granularity had a same impact on the metallization rate of the two material forms' reducing product.With the increase of reduction temperature,reduction time and the decrease of the raw ore granularity,the metallization rate of reducing products was gradually increasing.However,if the temperature or time exceeded a certain value,the metallization rate would decline slightly.Under the same reducing conditions,the metallization rate of briquetting was obviously higher than that of the loose ore as a result of better heat transfer and gas diffusion performance of briquetting.The gap of metallization rate between the both was gradually shrunken with increasing reduction temperature and the extending time.(3)The reduction temperature,reduction time,raw ore granularity had a same impact on grade and recovery of the two material forms' magnetic iron powder produced by coal-based reduction and magnetic separation,too.The grade and recovery of magnetic iron powder were gradually increasing with the increase of reduction temperature,reduction time and the decrease of the raw ore granularity.However,if the temperature or time exceeded a certain value,the separation indexes tended to be stable.The material form had significant effects on separation indexes of reduced product.Under the same reducing conditions,the separation indexes of briquetting were obviously higher than that of the loose ore.The gap of separation indexes between the both was gradually shrunken with increasing reduction temperature and the extending time.When the raw ore was loose,the best index of reducing conditions were shown as follows:raw ore granularity-0.1 mm,the reduction temperature 1275 ?,the reduction time 50 min,magnetic iron powder could be obtained by reducing product magnetic separation with grade 95.27%and recovery 95.13%;When the raw ore was briquetting,the best index of reducing conditions were shown as follows:raw ore granularity-0.1 mm,reduction temperature 1275 ?,the reduction time 50 min,magnetic iron powder could be obtained by reducing product magnetic separation with grade 95.57%and recovery 95.84%.(4)We systematically studied the iron grain size and morphology under the different reducing conditions and material forms by using scanning electron microscope and image software.This paper was supposed to provide that the reduction temperature,reduction time,raw ore granularity had a significantly impact on the growth of the two material forms'metallic iron particles.With the increase of reduction temperature,reduction time and the decrease of the raw ore granularity,the diameter of particles and quantity of large metal particle increased gradually and particle shapes became regular.Compared with loose ore,briquetting had advantages such as metal particle size was larger,shape of the particles was ruler,particle distribution was more uniform under the same reducing condition.Those indicated that briquetting form was more conducive to accumulation and growth of metallic iron.(5)The iron particles of two material forms' reducing products had the same the growth process.The shape change of iron particles experienced the evolution that single spherical granules,catenulate granules,block large particles,globular large particles.The metallic iron particles growth of reducing products was divided into two stages:A.Particle quantity was increased and a single iron particle grew;B.Motions of diffusion,migration,and link-fusion happened among iron particles.But briquetting was conducive to the evolution process.The research results of the paper have laid a certain theoretical foundation for choosing the material form in coal-based reduction of oolitic hematite and optimizing the process conditions.