Experimental Study On New Process Of Preparing High Purity Iron By Direct Reduction And Melting Separation Of Ultra-high Grade Iron Concentrate

High purity iron,an important raw material for soft magnetic materials,high purity precision and other materials,plays an important role in the healthy development of China's iron and steel industry because of its widely application in the field of aerospace and atomic industry.The industrial pure iron in our country is made from hot metal of blast furnace,which could hardly improve the quality and purity.The methods of electrolysis and physical purification have not yet achieved large-scale industrial production due to the resources and technical conditions in our country.High purity iron used in China is still heavily dependent on imports.Based on China's resources and technical conditions,a new process of preparing high pure iron by direct reduction and melting separation of ultra-high grade iron concentrate was put forward in this paper.First,the preparation process of pellets made from ultra-high grade iron concentrate was researched in the laboratory.The effects of roasting temperature and roasting time on compressive strength of pellets were investigated.Second,the gas based direct reduction experiments of pellets were carried out.The feasibility of applying ultra-high grade iron concentrate oxidized pellet to gas based direct reduction in shaft furnace was inspected.Third,the coal based direct reduction of ultra-high grade iron concentrate simulated tunnel kiln was studied.The process parameters,including reduction temperature,reduction time and the amount of sulfur fixing agent were considerated.The quality of high purity iron product was studied through the experimental study of melting separation.Based on the above research,the main conclusions were as follows:(I)Peridur was used as organic binder during pelletizing of ultra-high grade iron concentrate.The rational organic binder addition was 0.4%(mass).The drop number and compressive strength of the green pellets were 5.5 times and 17.5 N,respectively,which meets the requirements of roasting.(2)Roasting temperature and roasting time have significant influence on the comprehensive strength of ultra-high grade oxidized pellets.The suitable parameters were roasting temperature 1250? and roasting time 30 min.Under these conditions,the compressive strength of oxidized pellets was 2519 N,which can meet the requirements of gas based shaft furnace direct reduction process.(3)Although showing great reduction performance,ultra-high grade iron concentrate oxidized pellet have the problem of high reduction swelling index(51.20%in the system of reduction temperature 1050? and H2/CO=5/2).It could hardly meet the requirements of gas based shaft furnace direct reduction process.(4)During coal based tunnel kiln direct reduction process of the ultra-high grade iron ore concentrate?the metallization rate of direct reduction iron could reach above 95%under the conditions of 1000?1100? and 8?5 h.(5)The direct reduction iron produced by tunnel kiln process could be used for the preparation of high purity iron by melting method.Purity iron with iron content of 99.447%could be obtained with the conditions of melting temperature,time,and CaO addition are 1625?,45 min,and 9.3%,respectivele.