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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%.

This paper reports the recoveries of iron, chromium, and nickel from pickling sludge using coal-based smelting reduction. The influences of slag basicity (CaO/SiO2, which is controlled by high phosphorus oolitic hematite iron ores), reduction temperature, reduction time, and the C/O mole ratio on the recoveries of Fe, Cr, and Ni are investigated systematically. The experimental results show that high recoveries of Fe (98.91%), Cr (98.46%), and Ni (99.44%) are produced from pickling sludge with optimized parameters for the smelting reduction process. The optimized parameters are a slag basicity of 1.5; a reduction temperature of 1550 °C, a reduction time of 90 min, and a C/O mole ratio of 2.0. These parameters can be used as technical support for the recycling of pickling sludge with pyrometallurgy.

The paper proposes the innovative technology of hydrogen mineral phase transformation–magnetic separation–acid leaching for iron enrichment and dephosphorization, based on the mineralogical characteristics of high phosphorus oolitic hematite and difficulties that make it difficult to utilize traditional beneficiation for separation. The influences of the reduction temperature, reduction time, and reductant concentration during hydrogen mineral phase transformation on the separation index of high phosphorus oolitic hematite were investigated. The optimal conditions were determined to be a reduction time of 25 min with a reductant concentration of 30% and a reduction temperature of 540 °C, under which an iron grade of 65.05%, iron total recovery of 81.86%, and phosphorus content of 0.081% were obtained for the iron concentrate. The evolution of mineral phases, magnetic properties, and mineral microstructures was investigated by XRD, VSM, XPS, SEM, and BET. The results provide new references of technology and theoretical support for the efficient utilization of refractory iron ores.

Calcium carbonate, renowned for its affordability and potent dephosphorization capabilities, finds widespread use as a dephosphorization agent in the direct reduction roasting of high-phosphorus oolitic hematite (HPOIO). However, its precise impact on iron recovery and the dephosphorization of iron minerals with phosphorus within HPOIO, particularly the mineral transformation rule and dephosphorization mechanism, remains inadequately understood. This study delves into the nuanced effects of calcium carbonate on iron recovery and dephosphorization through direct reduction roasting and magnetic separation. A direct reduction iron (DRI) boasting 95.57% iron content, 93.94% iron recovery, 0.08% phosphorus content, and an impressive 92.08% dephosphorization is achieved. This study underscores how the addition of calcium carbonate facilitates the generation of apatite from phosphorus in iron minerals and catalyzes the formation of gehlenite by reacting with silicon dioxide and alumina, inhibiting apatite reduction. Furthermore, it increases the liquid phase, enhancing the dissociation of metallic iron monomers during the grinding procedure, thus facilitating efficient dephosphorization.

The efficient development and utilization of high-phosphorus oolitic hematite is of great strategic significance for the sustainable supply of iron-ore resources in China. In this paper, the mechanism of high-temperature pretreatment for enhancing the effect of iron enrichment and dephosphorization in the magnetization roasting-leaching process was studied by X-ray diffraction (XRD), vibration sample magnetometer (VSM), scanning electron microscopy and energy dispersive spectrometry (SEM-EDS). Compared with the process without high-temperature pretreatment, the iron grade of the magnetic separation concentrate after high-temperature pretreatment had increased by 0.98%, iron recovery rate had increased by 1.33%, and the phosphorus content in the leached residue had decreased by 0.12%. High-temperature pretreatment resulted in the dehydration and decomposition of hydroxyapatite, the dehydration of limonite and the thermal decomposition of siderite, which can produce pores and cracks and weaken the compactness of the ore, improve the magnetization characteristics of roasted ore, and strengthen the iron enrichment and dephosphorization during the magnetization roasting and leaching process.

In this paper, the process of direct reduction roasting using magnetic separation to produce direct reduction iron (DRI) from high-phosphorus oolitic hematite, using coal slime and blast furnace dust as reductant, is investigated. The possible use of slime coal and blast furnace dust as reductant and the dephosphorization behavior during the process of direct reduction was studied. Experimental results showed that both blast furnace dust and coal slime can be used as reductant under certain conditions in the process. The dephosphorization mechanism of blast furnace dust and coal slime were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM)-energy dispersive X-ray spectroscopy (EDS). A DRI with 91.88 wt. % iron grade, 88.38% iron recovery and 0.072 wt. % P can be obtained with 30 wt. % blast furnace dust as reductant. The program not only used blast furnace dust but also recovered iron from blast furnace dust and high-phosphorus oolitic hematite. The analysis results revealed that phosphorus is distributed in gangue mineral and fluorapatite when blast furnace dust is used as reductant. Phosphorus-bearing minerals were not reduced to phosphorus element when the blast furnace dust was the reductant, but part of the fluorapatite reduced to phosphorus which smelt into metallic iron with coal slime as reductant. This led to a high phosphorus content of DRI. This research could provide support to the idea concept for recycling of carbon-containing solid waste and to assist the effective recovery of refractory iron ore by direct reduction–magnetic separation.