Magnetizing Roasting Mechanism and Effective Ore Dressing Process for Oolitic Hematite Ore

Magnetizing roasting of oolitic hematite ore from western Hubei Province was investigated.The mechanism for reduction roasting of oolitic hematite ore was discussed and analyzed.It is found that flash magnetizing roasting-magnetic separation process is a promising approach for the processing of oolitic hematite ore from western Hubei Province.

Phase transformation in suspension roasting of oolitic hematite ore

Suspension roasting followed by magnetic separation is a promising method to upgrade oolitic hematite ore.An oolitic hematite ore was roasted using suspension roasting technology at different temperatures.The phase transformation for iron minerals was investigated by XRD and Mossbauer spectrum,and the characteristics of roasted product were analyzed by VSM and SEM-EDS.Results indicate that the magnetic concentrate is of 58.73% Fe with iron recovery of 83.96% at 650 °C.The hematite is rapidly transformed into magnetite during the roasting with transformation ratio of 92.75% at 650 °C.Roasting temperature has a significant influence on the phase transformation of hematite to magnetite.The transformation ratio increases with increased temperature.After roasting,the magnetic susceptibility is significantly improved,while iron ore microstructure is not altered significantly.

Synchronous enrichment of phosphorus and iron from a high-phosphorus oolitic hematite ore to prepare Fe-P alloy by direct reduction-magnetic separation process

In this study,direct reduction-magnetic separation process was applied to enrich phosphorus and iron to prepare Fe-P crude alloy from a high phosphorus oolitic hematite ore(HPOH).The results show that at lower temperatures and with absence of any of additives,Fe cannot be effectively recovered because of the oolitic structure is not destroyed.In contrast,under the conditions of 15%Na_(2)SO_(4)and reducing at 1050℃ for 120 min with a total C/Fe ratio(molar ratio)of 8.5,a final Fe-P alloy containing 92.40%Fe and 1.09%P can be obtained at an overall iron recovery of 95.43%and phosphorus recovery of 68.98%,respectively.This metallized Fe-P powder can be applied as the burden for production of weathering resistant steels.The developed process can provide an alternative for effective and green utilization of high phosphorus iron ore.

Direct Reduction of High-phosphorus Oolitic Hematite Ore Based on Biomass Pyrolysis

Direct reduction of high-phosphorus oolitic hematite ore based on biomass pyrolysis gases （CO, H2, and CH4 ）, tar, and char was conducted to investigate the effects of reduction temperature, iron ore-biomass mass ratio, and reduction time on the metallization rate. In addition, the effect of particle size on the dephosphorization and iron recovery rate was studied by magnetic separation. It was determined that the metallization rate of the hematite ore could reach 99.35 % at iron ore-biomass mass ratio of 1 ： 0.6, reduction temperature of 1100℃, and reduction time of 55 min. The metallization rate and the aggregation degree of iron particles increase with the increase of reduction temperature. The particle size of direct reduced iron （DRI） has a great influence on the quality of the iron concentrate during magnetic separation. The separation degree of slag and iron was improved by the addition of 15 mass% sodium carbonate. DRI with iron grade of 89.11%, iron recovery rate of 83.47%, and phosphorus content of 0.28% can be obtained when ore fines with particle size of -10μm account for 78.15%.

Prediction of density and volume variation of hematite ore particles during in-flight melting and reduction

HIsarna is a promising ironmaking technology to reduce CO2 emission.Information of phase transformation is essential for reaction analysis of the cyclone reactor of the HIsarna process.In addition,data of density and volume of the ore particles are necessary for estimation of the residence time of the particles in the cyclone reactor.Phase transformation of iron ore particles was experimentally studied in a drop-tube furnace under simulated cyclone conditions and compared with thermodynamic calculation.During the pre-reduction process inside the reactor,the mineralogy of iron ore particles transforms sequentially from hematite to sub-oxides.The density changes of the particles during the melting and reduction can be predicted based on the phase composition and temperature.Therefore,density models in the studies were evaluated with reported experimental data of slag.As a result,a more reliable density model was developed to calculate the density of the formed slag containing mainly FeO–Fe2O3.The density and volume of the partially reduced ore particles or melt droplets were estimated based on this model.The results show that the density of the ore particles decreases by 15.1%at most along the progressive reduction process.Furthermore,the model results also indicate that heating,melting and reduction of the ore could lead to 6.63%–9.37%swelling of the particles,which is mostly contributed by thermal expansion.It would result in corresponding variation in velocity of the ore particles or melt droplets during the flight inside the reactor.

Application of multi-stage dynamic magnetizing roasting technology on the utilization of cryptocrystalline oolitic hematite:A review

A large number of studies have shown that oolitic hematite is an iron ore that is extremely difficult to utilize because of its fine disseminated particle size, high harmful impurity content and oolitic structure.To recover iron from oolitic hematite, we developed a novel multistage dynamic magnetizing roasting technology. Compared with traditional magnetizing roasting technologies, this novel technology has the following advantages: firstly, the oolitic hematite is dynamically reduced in a multi-stage roasting furnace, which shortens the reduction time and avoids ringing and over-reduction;secondly, the novel dynamic magnetizing roasting technology has strong raw material adaptability, and the size range of raw materials can be as wide as 0–15 mm;thirdly, the roasting furnace adopts a preheating-heating process, and the low-calorific value blast furnace gas can be used as the fuel and reductant, which greatly reduces the cost. The actual industrial production data showed that the energy consumption in the roasting process can be less than 35 kg of standard coal per ton of raw ore. The iron grade of the concentrate and iron recovery reached 65% and 90%, respectively.

Reduction behavior of hematite in the presence of coke

The reduction kinetics of hematite in the presence of coke as a reductant was studied via isothermal and non-isothermal thermodynamic analyses. The isothermal reduction of hematite was conducted at a pre-determined temperature ranging from 1423 to 1573 K. The results indicated that a higher reduction temperature led to an increased reduction degree and an increased reduction rate. The non-isothermal reduction of hematite was carried out from room temperature to 1573 K at various heating rates from 5 to 15 K·min^（-1）. A greater heating rate gave a greater reduction rate but decreased reduction degree. With an increase in temperature, both the reduction rate and the reduction degree increased at a smaller rate when the temperature was less than 1150 K, and they increased at a higher rate when the temperature was greater than 1150 K before completion of the reduction reaction. Both the isothermal and the non-isothermal reduction behaviors of hematite were described by the Avrami–Erofeev model. For the isothermal reduction, the apparent activation energy and pre-exponential factor were 171.25 kJ ·mol^（-1） and 1.80 × 10~5 min^（-1）, respectively. In the case of non-isothermal reduction, however, the apparent activation energy and pre-exponential factor were correlated with the heating rate.

Recent collaborative researches between Japanese universities and steel industry on the iron ore agglomeration process

The properties of iron ores used in ironmaking process have been drastically changed in the past couple of decades.Especially,the change has become significant in the last few years because of the considerable increase in the world steel production.The property change of the iron ore is mainly caused by the depletion of the hard and high-grade lump hematite ores.It has led to the increasing use of ores containing a larger amount of goethite/limonite,i.e.,hydro-oxides of iron.Typically,the proportion of pisolitic ores,which are course limonitic ores,has remarkably increased by several times in Japan.Further,large deposits of the fine goethite ores called Marra Mamba have been developed in Australia and exported to Asian countries.Such trends will be continued in future.Since the change of the ore properties affects not only to the productivity and yield of the sinter but also its metallurgical properties in the blast furnace,further improvement in the sintering technology/ process is required including the preliminary treatment process of raw materials.In order to make wide researches concerning the above issues,the research project 'New Sintering Process through Designing of Composite Granulation & Bed Structure' was formed in the ISIJ,which was the collaborative project between Japanese steel companies and several universities.The project was started in 2005 and carried on the wide range of studies for three and half years.Its main objects are the characterization of pisolitic/goethitic ores and the understanding the behavior during the iron ore sintering process.Further,considering the ore characteristics,some basic researches on the optimum designs of raw material blending,granulation,bed structure,and the metallurgical properties of the produced sinter were performed.The project have invented the technical principle of a new sintering process, namely MEBIOS(Mosaic EmBedding Iron Ore Sintering Process),characterized by the composite granulation and bed-structure,aiming to cope with the drastic shift of the ore properties.Another big issue fallen on the steel industry is the global warming.CO,emission from steelmaking industry occupies about 15%of the total value of the artificial emissions in Japan and therefore its reduction is urgently required.In order examine the possibility to minimize or to reduce further the CO_2 emission from the iron ore sintering process,the research project 'Technological Principle for Low-Carbon Sintering' has been formed since 2009 in the ISIJ.In this project,the analyses of the combustion rates of carbonaceous materials and heat transfer in the sintering bed are first examined by referring the previous studies.Further,experimental works will be conducted on the combustion/oxidation characteristics of biomass charcoal,some organic wastes,steel can scraps,mill scale and partially reduced iron ores as alternative agglomeration reagents of coke and anthracite coal.The effect of their use on the sintering process will be evaluated systematically.It is expected that the structural changes of the sintering bed is considerably different between carbonaceous materials,which disappear during combustion leaving a little amount of ash components and metallic iron bearing materials,which increase the mass and volume during its oxidation. Previous studies showed that the use of metallic iron bearing materials such as steel can scrap and mill scale led to significant decreases in the production rate.This project examines the characteristics of such changes of the sintering bed structure and mineral phases and main process parameters,which govern such phenomena.Further, it searches for a new process principle to overcome the demerits and realize the significant reduction of CO_2 emissions from the iron ore sintering process.In the symposium,summary of activities and the major results and progresses of the above two research projects will be introduced.

Separation of hematite from banded hematite jasper(BHJ) by magnetic coating

The separation of iron oxide from banded hematite jasper(BHJ) assaying 47.8% Fe, 25.6% Si O2 and 2.30%Al2O3 using selective magnetic coating was studied. Characterization studies of the low grade ore indicate that besides hematite and goethite,jasper, a microcrystalline form of quartzite, is the major impurity associated with this ore. Beneficiation by conventional magnetic separation technique could yield a magnetic concentrate containing 60.8% Fe with 51% Fe recovery. In order to enhance the recovery of the iron oxide minerals, fine magnetite, colloidal magnetite and oleate colloidal magnetite were used as the coating material. When subjected to magnetic separation, the coated ore produces an iron concentrate containing 60.2% Fe with an enhanced recovery of56%. The AFM studies indicate that the coagulation of hematite particles with the oleate colloidal magnetite facilitates the higher recovery of iron particles from the low grade BHJ iron ore under appropriate conditions.