Study On Microwave Drying And Preheating Of Iron Ore Pellet Containing Organic Binder

Steel industry is one of the fundamental industries in our country.In recent years,the expanding pellet production increases for iron making. By far pellet factories use bentonite as binder,the total Fe in pellet is decreased.It's an efficient way to increase it by using organic binder instead of bentonite.But the strength of iron pellet with organic binder is not good during the drying and preheating phase by traditional method, which influences the application of pellet production with organic binder. Microwave heating makes it possible to solve the problems in pellet production with organic binder.When drying pellet with organic binder by microwave heating, microwave was selectively absorbed by the moisture in the pellet in relatively lower temperature.And the moisture in the pellet vaporized fast. Moreover,microwave drying might not damaged the molecular structure of the organic binder,which kept the strength of the pellet.Drying tests showed that when the microwave power was 0.7kW,the materiel weight was 0.5kg,it spended 12 minutes in drying pellet,and the pellet compression strength was 38.65N/P which was 3.5 times than that of pellet by updraught drying.While updraught drying can finish the same work in 14 minutes under the temperature of 300℃and wind speed 1.0m/s.The pellet compression strength was 10.92N/P.The polar particulate in the iron ore pellet acutely vibrate in magnetic field,which increased the particle diffusion and accelerate the oxidation of magnetite.With microwave power of 2.5 kw,material weigth of 0.4 kg,heating for 15min,the ultimate temperature of the pellet was 1060℃, pressure resistence was 1554N/P,AC tumbler index was 0.52%.However, it showed that the AC tumbler index of pellet was 58.89%obtained by muffle preheating with temperature 1050℃and heating time 15 minutes. Using tube furnace preheating,the compression strength was 433N/P under the temperature of 1050℃and heating for 15 minutes.The compression strength of pellet by microwave preheating is 3.6 times than that of pellet by tube furnace preheating. Analysis of the microstructure of pre-heated pellet using optical microscope and SEM showed that,with tube furnace preheating,when heating temperature was low than 1100℃,heating time was 15 minutes, the magnetite in pellet was nor fully oxidized,newly formed Fe₂O₃ was few and granule,and the distance between particles was large.Using microwave preheating,with microwave power 2.5kw,ultimate temperature of the pellet was 1060℃,and the mineral sturcure was homoheneous.Magnetite ore was oxidized to hematite and most hematie was connected well.So the pre-heated pellet has high strength.