A new method of utilizing high-silica hematite to produce low-silicon molten iron was proposed.In this method,FASTMELT,which comprised direct reduction and melt separation processes,was applied,with highly reactive biochar as the reductant in the direct reduction stage.The proposed method was experimentally investigated and the results show that the method is feasible.In the direct reduction stage,ore-char briquette could achieve a metallization rate of 84%-88% and residual carbon of 0.27-0.89mass% at temperature of 1373 K,biochar mixing ratio of 0.8-0.9,and reduction time of 15 min.Some silica particles remained embedded in the iron phase after the reduction.In the melting separation stage,molten iron with a carbon content of 0.02-0.03mass% and silicon content of 0.02-0.18mass%could be obtained from the metallic briquettes under the above-mentioned conditions;the iron recovery rate was83%-91% and impurities in the obtained metal were negligible.
Gaseous reduction kinetics of the high phosphorus iron ore fines from Hubei in China and effect of microwave pretreatment on the gaseous reduction behavior were studied. Gaseous reduction kinetics were investigated by TG (Thermogravimetric) methods using LINSEIS STA PT 1600 thermal analysis equipment. Microwave pretreatments to the ore fines with four power levels were performed using a high temperature microwave reactor. Its effect was examined by TG methods and its mechanism was analyzed by SEM (scanning electron microscope) and EDS (energy dispersive spectrometer). Gaseous reduction tests were carried out using a tubular furnace. Results of kinetic study indicate that controlling step of the gaseous reduction of the ore fines is a mixing control of gas internal diffusion and interface chemical reaction when reduction fraction is less than 0.8 and is solid state diffusion when reduction fraction is more than 0.8. Microwave pretreatment of the ore fines could change the pore structure of the oolitic unit to generate cracks, fissures and loose zones, which promotes reduction in the early stage and delays the occurrence of sintering. Gaseous reduction tests show in the condition that the ore fines are pretreated with a microwave power of 450 W for 4 min and reduced under temperature of 1 273 K, the gaseous reduction of the ore fines could be apparently intensified. Using CO or H2 as a reductant and ore fines being reduced for 1.5 to 2 h , increase of metallization rate of the ore fines is 10% to 13%.
Slag/metal separation process of the highly reduced oolitic high-phosphorus iron ore fines was investigated.Samples were prepared using the reduced ore fines(metallization rate:88%)and powder additives of CaO and Na2CO3.Slag/metal separation behavior tests were conducted using aquenching method and the obtained metal parts were subjected to direct observation as well as microstructure examination with SEM and EDS;iron recovery and phosphorus distribution tests were conducted using a Si-Mo high temperature furnace and the obtained metal parts were examined by ICP-AES analysis and mass measurement.Thermodynamic calculation using coexistence theory of slag structure was also performed.Results show that temperature for slag/metal separation must be higher than1 823 Kand a satisfying slag/metal separation of the highly reduced ore fines needs at least 4min;phosphorus content of hot metal is mainly determined by thermodynamics;temperature of 1 823-1 873 Kand Na2CO3 mixing ratio of about 3% are adequate for controlling phosphorus content to be less than 0.3mass%in hot metal;temperature,time and Na2CO3 mixing ratio do not have significant effect on iron recovery,and iron recovery rate could be higher than 80% as long as a good slag/metal separation result is obtained.
