Jue Kou

Study on Phosphorus Removal of High-Phosphorus Oolitic Hematite by Coal-Based Direct Reduction and Magnetic Separation

In this article, mineralogical phase changes and structural changes of iron oxides and phosphorus-bearing minerals during the direct reduction roasting process were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). It has been found that the reduction of hematite follows the following general pathway: Fe2O3 → Fe3O4 → FeO → Fe. The last step of the reduction process contains two side reactions: either FeO → Fe2SiO4 → Fe or FeO → FeAl2O4 → Fe depending on the micro mineralogical makeup of the ore. In the reduction process of FeO → Fe, oolitic structure was destroyed completely and fluorapatite was diffused into gangue while metallic phase is coarsening at temperatures below 1200°C. Therefore, the separation of phosphorus-bearing gangue and metallic iron can be achieved by wet grinding and magnetic separation, and low phosphorus content metallic iron powder can be obtained. However, when the temperature reached 1250°C and beyond, some of the fluorapatite was reduced to elemental P and diffused into the metallic iron phase, making the P content higher in the metallic iron powder.

Study on the strength of cold-bonded high-phosphorus oolitic hematite-coal composite briquettes

Composite briquettes containing high-phosphorus oolitic hematite and coal were produced with a twin-roller briquette machine using sodium carboxymethyl cellulose, molasses, starch, sodium silicate, and bentonite as binders. The effect of these binders on the strength of the composite briquettes, including cold strength and high-temperature strength, was investigated by drop testing and compression testing. It was found the addition of Ca(OH)2 and Na2CO3 not only improved the reduction of iron oxides and promoted dephosphorization during the reduction-separation process but also provided strength to the composite briquettes during the briquetting process; a compressive strength of 152.8 N per briquette was obtained when no binders were used. On this basis, the addition of molasses, sodium silicate, starch, and bentonite improved the cold strength of the composite briquettes, and a maximum compressive strength of 404.6 N per briquette was obtained by using starch. When subjected to a thermal treatment at 1200°C, all of the composite briquettes suffered from a sharp decrease in compressive strength during the initial reduction process. This decrease in strength was related to an increase in porosity of the composite briquettes. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses showed that the decrease in strength of the composite briquettes could be caused by four factors: decomposition of bonding materials, gasification of coal, transportation of byproduct gases in the composite briquettes, and thermal stress.

Effects of Na2SO4 on iron and nickel reduction in a high-iron and low-nickel laterite ore

This study investigates the reactions of Na2SO4 and its effects on iron and nickel reduction in the roasting of a high-iron and low-nickel laterite ore through gas composition, X-ray diffraction, and scanning electron microscope analyses. Results showed that a reduction reaction of Na2SO4 to SO2 was performed with roasting up to 600°C. However, no clear influence on iron and nickel reductions appeared, because only a small amount of Na2SO4 reacted to produce SO2. Na2SO4 reacted completely at 1000°C, mainly producing troilite and nepheline, which remarkably improves selective reduction of nickel. Furthermore, the production of low-melting-point minerals, including troilite and nepheline, accelerated nickel reduction and delayed iron reduction, which is attributed to the concurrent production of magnesium magnetite, whose structure is more stable than the structure of magnetite. Reduction reactions of Na2SO4 resulted in weakening of the reduction atmosphere, and the main product of Na2SO4 changed and delayed the reduction of iron. Eventually, iron metallization was effectively controlled during laterite ore reduction roasting, leading to iron mainly being found in wustite and high iron-containing olivine.

Industry Test on Phosphorus Removal and Direct Reduction of High-Phosphorus Oolitic Hematite Ore

Industry test on phosphorus removal and direct reduction of the “Ningxiang type” high-phosphorus oolitic hematite ore has been carried out in a tunnel kiln on the basis of laboratory experiment. The iron grade and phosphorus content of the initial sample are 42.46% and 0.867%, respectively. The results showed that high-phosphorus oolitic hematite could be exploited on industrial scale, with the new process direct reduction roasting – grinding – magnetic separation, and that the final concentrate with an iron grade 92.56%, iron recovery 82.77% and phosphorus content 0.089% was obtained under the optimal conditions. Besides, X-ray diffraction (XRD) and scanning electron microscope with X-ray energy dispersive spectrum (SEM-EDS) were used to analysis the mechanism of phosphorus removal and direct reduction. It was shown that oolitic structure was destroyed, and metallic iron particle coarsening was obvious, besides fluorapatite particles were dispersed in the gangue by diffusion during the reduction roasting process. The liberation of metallic iron and gangue can be achieved by grinding, so high iron grade and low phosphorus content concentrate can be obtained after magnetic separation.

Studies on the Effects of Particle Size in Direct Reduction Roasting of Limonite Ores

A series of direct reduction roasting - magnetic separation tests were carried out with refractory limonite ore in two different particle size compositions. The effect of particle size in the grade and recovery of direct reduced iron (DRI) at different roasting time, temperature and reductant dosages was investigated, and the mineralogical transformations of DRI obtained at different roasting time were analyzed using scanning electron microscopy (SEM-EDS). The results demonstrate that direct reduction roasting with limonite ore in large particle size (100% －20mm) was feasible, and the reducibility of limonite ore in large particle size increased with increasing reductant dosage and roasting time. The optimum reduction roasting - magnetic separation parameters of 100%－20mm limonite ore were proposed as the following: roasting at 1200°C for 120min with 40% reductant, and milling 30min followed by low intensity magnetic separation, which resulted in the DRI with TFe grade of 90.2% and recovery of 89.3%.

Feasibility of co-reduction roasting of a saprolitic laterite ore and waste red mud

Large scale utilization is still an urgent problem for waste red mud with a high content of alkaline metal component in the future. Laterite ores especially the saprolitic laterite ore are one refractory nickel resource, the nickel and iron of which can be effectively recovered by direct reduction and magnetic separation. Alkaline metal salts were usually added to enhance reduction of laterite ores. The feasibility of co-reduction roasting of a saprolitic laterite ore and red mud was investigated. Results show that the red mud addition promoted the reduction of the saprolitic laterite ore and the iron ores in the red mud were co-reduced and recovered. By adding 35wt% red mud, the nickel grade and recovery were 4.90wt% and 95.25wt%, and the corresponding iron grade and total recovery were 71.00wt% and 93.77wt%, respectively. The X-ray diffraction (XRD), scanning electron microscopy, and energy dispersive spectroscopy (SEM-EDS) analysis results revealed that red mud addition was helpful to increase the liquid phase and ferronickel grain growth. The chemical compositions “CaO and Na2O” in the red mud replaced FeO to react with SiO2 and MgSiO3 to form augite.

Effect of Na2CO3 and CaCO3 on coreduction roasting of blast furnace dust and high-phosphorus oolitic hematite

Iron was recovered from blast furnace dust and high-phosphorus oolitic hematite in the presence of Na2CO3 and CaCO3 additives. The functions of Na2CO3 and CaCO3 during the coreduction roasting process were investigated by XRD and SEM-EDS analyses. Results indicate that these additives not only hinder the reduction of fluorapatite, CaCO3 also decreases the P content of direct reduced iron (DRI) by increasing the reduction alkalinity. P remains as fluorapatite in the slag, which can be removed by grinding and magnetic separation under optimal conditions. The Na2CO3 promotes hematite reduction and improves the iron recovery (εFe) by replacing the FeO from fayalite, which results in quick growth and aggregation of metallic iron and improvement of εFe in DRI. A DRI with 91.88 mass% Fe, and 0.065 mass% P can be achieved at a recovery of 87.86 mass% under the optimal condition.

Effects and mechanisms of fluorite on the co-reduction of blast furnace dust and seaside titanomagnetite

The co-reduction roasting and grinding magnetic separation‒of seaside titanomagnetite and blast furnace dust was investigated with and without fluorite addition at a reduction roasting temperature of 1250°C for 60 min, a grinding fineness of −43 μm accounting for 69.02wt% of the total, and a low-intensity magnetic field strength of 151 kA/m. The mineral composition, microstructure, and state of the roasted products were analyzed, and the concentrations of CO and CO2 were analyzed in the co-reduction roasting. Better results were achieved with a small fluorite dosage (≤4wt%) in the process of co-reduction. In addition, F− was found to reduce the melting point and viscosity of the slag phase because of the high content of aluminate and silicate minerals in the blast furnace dust. The low moisture content of the blast furnace dust and calcic minerals inhibited the hydrolysis of CaF2 and the loss of F−. Compared with the blast furnace dust from Chengdeng, the blast furnace dusts from Jiugang and Jinxin inhibited the diffusion of F− when used as reducing agents, leading to weaker effects of fluorite.

Mechanism Research on Niobium Distribution Influenced by Roasting Temperature in the Direct Reduction Roasting Process

In this study, the niobium enrichment research of the iron concentrate containing niobium was studied by coal-based direct reduction roasting followed by magnetic separation process. The distribution of niobium element and existence form of mineral bearing-Nb in roasted products were investigated under different roasting temperature which was ranging from 1100°C to 1300°C. X-ray diffraction analysis (XRD) was used to identify the various minerals and compositions of the roasted products. The microstructures of these products were analyzed by the scanning electron microscope (SEM), while the elemental analysis was carried out by using energy dispersive spectrometer (EDS) technique. The results of XRD and EDS analysis showed that most of the niobium minerals were Nb-Fe rutile and ulvospinel which scattered in slag, and only a little was adhered to the surface of metallic iron at 1100°C. And the niobium oxides were partly reduced to Ti-aeschynite and niobocarbide which attached on the surface of metallic iron, and most were still ulvospinel scattering in the slag at 1200°C. The Ti-aeschynite was gradually reduced to Nb adhering to the metallic iron particle forming Nb-Fe soild solution at 1300°C.