Effect Of Patassium Feldspar On The Swelling Properties Of Reduced Iron Oxide In CO Stage

The Barrun Mine is a composite ore of symbiosis of various minerals such as iron,rare earth and strontium.It contains more alkali metals?Na,K?than ordinary mines.Among them,the special components have a serious impact on the preparation process of the pellets,as well as the physical properties and metallurgical properties of the pellets,especially the reduction and swelling of the pellets.Potassium feldspar is complex in composition and contains more alkaline metal oxides such as K₂O and Na₂O,which have similar properties to Barrun Mine.In this paper,the effect of potassium feldspar on the reduction and swelling properties of iron oxides was studied.According to the gas phase equilibrium composition of Fe-O-C system,the reduction system at different stages was determined and phased reduction was carried out.Fe₃O₄ was used as the base material,and0%,4%,8%,and 12%potassium feldspar were added respectively.After mixing,they were pressed into strips and calcined in a tubular resistance furnace at 1250°C for 30 min.O₂ was introduced into the roasting process at a flow rate of 50 mL/min to fully oxidize Fe₃O₄ to Fe₂O₃.The CO was used as the reducing gas,and the swelling ratio in the reduction process was measured by a PCY-G high-temperature vacuum dilatometer.During the reduction process,the swelling displacement changes,and the curve of the swelling displacement change was drawn using the origin 8 software.The effects of potassium feldspar on the reduction and swelling of CO-graded iron oxides were systematically studied by means of thermodynamic software FactSage,XRD and SEM.Fe₂O₃?Fe₃O₄ was reduced at 600°C for 1 h,and the ratio of CO gas to CO₂ gas flow was 1:4.Actually,60 mL/min CO and 240 mL/min CO₂ gas were respectively introduced.The reduction swelling ratios of 0%,4%,8%,and 12%potassium feldspar were 2.19%,2.16%,2.13%,and 2.11%,respectively,and the reduction swelling ratio decreased with the increase of potassium feldspar ratio.The microscopic morphology of each sample was observed by SEM,and it was found that the surface cracks and grains gradually decreased with the increase of potassium feldspar content.The swelling of the first stage of reduction is mainly caused by the change of crystal structure.The addition of potassium feldspar is equivalent to the addition of slag phase,and the resulting slag phase fills pores and grains hinder the change of lattice structure.With the increase of potassium feldspar ratio.The linear swelling rate does not change significantly.Fe₃O₄?FeO was reduced on the basis of the first stage,and then reduced at 900°C for 1 h.The ratio of CO gas to CO₂ gas flow was 3:2,and 180 mL/min CO and 160mL/min CO₂ gas were actually introduced respectively.The reduction swelling ratios of0%,4%,8%,and 12%potassium feldspar were-0.51%,-0.11%,0.11%,and 0.46%,respectively,and the reduction swelling ratio increased with the increase of potassium feldspar ratio.The microscopic morphology of each sample was observed by SEM,and it was found that with the increase of potassium feldspar content,the crystallites gradually decreased,the cracks increased,and the volume increased.The swelling ratio of each sample did not change much,mainly because both Fe₃O₄ and FeO were cubic,so the volume change was small.FeO?Fe is reduced on the basis of the second stage,and then reduced at 900°C for 1h,and 300 mL/min CO gas is added,and the reduction swelling ratios of 0%,4%,8%,and12%potassium feldspar are respectively-6.26%,-4.42%,-2.40%and-1.68%,the overall shrinkage.the reduction swelling rate increases with the increase of potassium feldspar ratio.The nascent metal iron liquid phase will aggregate to shrink the volume of the sample.With the addition of different content of potassium feldspar,the slag phase will appear in the sample during the roasting process,and the Fe₂SiO₄ hard-reducing substance will also appear in the reduction process due to the slag phase.Since the slag phase does not participate in the reduction,many"slag walls"are formed inside to hinder the aggregation of the metal iron,inhibit the shrinkage,and promote the swelling.In this paper,by studying the effect of potassium feldspar on the reduction and swelling of CO-reduced iron oxides,the linear swelling rates were-4.58%,-2.37%,0.16%and 0.89%during the whole reduction process,and The overall linear swelling rate increases with the increase of potassium feldspar content.The addition of potassium feldspar promotes the swelling of reduced iron oxide.