Direct Reduction-magnetic Separation Research Articles

Mechanism of iron grains aggregation and growth in metalized pellet under the alternating magnetic fields

The direct reduction-magnetic separation method is highly efficient for producing metallic iron powder from low-grade complex ore resources. However, the limitation lies in the small average size of iron grains, which impedes the subsequent separation between metallic iron and gangue minerals. To address this, a novel method utilizing induction heating was introduced to stimulate the aggregation and growth of iron grains. Our study systematically investigated the growth kinetics behavior of iron grains under alternating magnetic fields. Additionally, we compared the impact of induction heating versus conventional heating on iron grain growth and delved into the mechanism through which the magnetic effect enhances the aggregation and migration of iron grains. The results indicate that iron grains can effectively aggregate and migrate to the edges of cracks or pellet surface under alternating magnetic fields, realizing the increase of average iron grain size and the pre-separation of metallic iron from gangue minerals. Specifically, the average iron grain size increased from 12.95 μm to 36.58 μm when induction heating temperature at 1300 °C for 100 min. Additionally, the total iron grade of concentrate reached 94.60% with ball milling 30 min and magnetic field intensity of 750 Gs. Finally, the growth model of iron grains under alternating magnetic fields was established and the mechanism of magnetic effect on promoting iron grains growth was revealed.

Chromium and iron recovery from hazardous extracted vanadium tailings via direct reduction magnetic separation

The large accumulation of extracted vanadium tailings not only causes a waste of resources but also leads to environmental pollution. In this work, a technique was proposed that involves direct reduction followed by magnetic separation for recovering Fe and Cr while removing Na from the extracted vanadium tailings. Thermodynamic analysis and process parameters such as the use of additives and the reduction temperature were experimentally determined. Thermodynamic results showed that a reduction temperature higher than 1250 °C is required for the simultaneous removal of sodium, iron, and chromium. The experimental results indicated that when the Ca (OH)2 addition was added at a rate of 30 %, and the reduction temperature was maintained at 1350 °C for 2 h, Fe-Cr alloys were formed by the reduction of iron and chromium and could be separated by magnetic separation. The addition of Ca (OH)2 greatly facilitates the reduction of the Fe-containing phase in the extracted vanadium tailings, resulting in the formation of Fe-Cr alloy with reduced Cr. Sodium metal was volatilized, with removal rates of 65.9 %, 93.3 % and 93.32 % for Cr, Fe and Na, respectively. The recovery efficiencies for Fe and Cr were 85.9 % and 65.4 % respectively. The magnetic concentrate contained 83.84 % total Fe and 7.25 % Cr, and its main phase was Fe-Cr alloy. In contrast, the magnetic tailing consisted mainly of CaTiO3. The simultaneous method has a significant impact on removing valuable metals and reducing the environmental risk of the extracted vanadium tailings.

A detoxification and value-added process for chromium ore processing residue (COPR) and Fe-C-bearing dust: Direct reduction-magnetic separation

Chromium ore processing residue (COPR), containing much virulent hexavalent chromium [Cr(VI)], is a by-product derived from chromate production. Fe-C-bearing dust from steel industry is very difficult to be utilized effectively because of its complex composition and unstable properties. The dust was co-processed with COPR by a direct reduction-magnetic separation process in this study. Through the strong reducing ability of solid carbon in Fe-C-bearing dust, the compounds of Cr and Fe were reduced to (Cr, Fe)7C3 alloy during the reduction roasting process and then selectively recovered by magnetic separation. In addition, the Pb and Zn compounds were reduced and volatilized into flue gas at high temperature. Under the optimal conditions, the results indicated that Cr-containing iron powder with 72.59 % Fe and 6.34 % Cr was obtained, and the recoveries of Fe and Cr were respectively 79.1 % and 76.9 %. The volatilization rates of Pb and Zn met 97.47 % and 99.95 %, respectively. The non-magnetic tailings were determined to be nontoxic and could be used as high-quality raw materials for building.

Improvement of Carbothermic Reduction of Copper Smelting Slag and Valuable Constituents Recovery

In order to comprehensively utilize copper smelting slag, the effect of strengthening measures on the reduction rate of the copper smelting slag, reduction kinetics, magnetic separation of reduced pellet and volatilization of residual valuable constituents were investigated in the present study. Milling for mechanical activation was the most efficient method to improve the reduction rate of copper smelting slag compared to addition of Na2CO3 catalyst and high reactivity reducing agent. The metallization degree of reduced pellet increased from 54.5% to 75.5% when the slag-coal mixture was milled for 30 s and reduced at 1100°C for 30 min. The apparent activation energy for the reduction of milled pellet increased from 96.1 kJ/mol to 153.5 kJ/mol. The iron concentrate magnetically separated from the milled pellet reduced at 1200°C had the best quality. The removal rates of typical elements during direct reduction-magnetic separation decreased in the sequence of Zn>K>Na>Cu. Secondary-dust captured from the flue gas contained 70.17 mass% Zn and 11.99 mass% Pb, which could meet the requirements of I grade zinc ore. The Zn in the dust existed in the form of ZnO. The productivity of the dust was around 1.49%. The application of mechanical milling in the reduction of copper smelting slag/coal composite pellet can improve the reduction efficiency of iron oxide and the quality of Zn-rich secondary dust. This work can help to enhance the utilization of copper smelting slag in a more efficient and sustainable method.

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

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

Upgrade of nickel and iron from low-grade nickel laterite by improving direct reduction-magnetic separation process

Upgrade of nickel and iron from low-grade nickel laterite by improving direct reduction-magnetic separation process

Effective and economical treatment of low-grade nickel laterite by a duplex process of direct reduction-magnetic separation & rotary kiln-electric furnace and its industrial application

An innovative technical route has been proposed to improve recycling efficiency of Ni and Fe from low-grade nickel laterite via the duplex process between direct reduction-magnetic separation and rotary kiln-electric furnace. The results indicated that the high‑nickel concentrates produced from direct reduction-magnetic separation process, which were combined with optimization of slag types can not only increase the grade of furnace burdens and decrease quantity of slag, but also improve the fluidity of slag and smelting efficiency as well as reduce the power consumption of smelting. For the industrial application of duplex process, a preferable stainless-steel master alloy with 10.02% Ni was obtained at a lower cost of 8420 RMB/t than that of 8731 RMB/t for a stainless-steel master alloy containing 8.14% Ni in conventional rotary kiln-electric furnace process, and the recovery of nickel also increased from 91.27% to 95.51%, which shows an obvious superiority for treating the low-grade nickel laterite.

Reductive roasting mechanism of copper slag and nickel laterite for Fe-Ni-Cu alloy production

Direct reduction-magnetic separation process (DRMSP) is a highly effective and clean method to upgrade the complex resources, which has been widely used to recovery the value metals in copper slag (CS) and nickel laterite (NL) in recent years. Adequate growth of the alloy particles is a key parameter influencing the complete extraction of alloys from CS and NL in this process. Therefore, the liquid phase formation mechanism, growth kinetics of the alloy particles, and the correlation between the alloy particle growth and liquid phase formation were studied to reveal the synergistic effect of the co-reduction of CS and NL. The results indicated that fayalite in the copper slag reacted with forsterite in nickel laterite to form augite group minerals with low melting points, resulting in more liquid phase formation in the reductive roasting process. A comparison with the reduction kinetic parameters of the single nickel laterite showed that the growth index and activation energy decreased significantly from 2.85 and 272.98 KJ/mol to 2.08 and 171.99 KJ/mol, respectively, after the addition of 40% copper slag, which confirmed that copper slag promoted the particle growth. Moreover, the liquid phase increased the total cohesive force between the alloy particles, revealing the correlation between alloy particle growth and liquid phase.

Carbonization and nitridation of vanadium–bearing titanomagnetite during carbothermal reduction with coal

Direct reduction–magnetic separation followed by low temperature chlorination was a promising process to comprehensively utilize vanadium–bearing titanomagnetite (VTM). Herein, the conversion of titanium oxides to TiC/TiN/Ti(C,N) is extremely critical. In this study, the carbonization and nitridation of VTM during carbothermal reduction under different atmosphere was investigated. Thermodynamic analysis indicated that the reduction, carbonization and nitridation of VTM was feasible via carbothermal reduction by carbon. Introducing N2 into the reaction system was beneficial to decrease the equilibrium temperature by forming TiN instead of TiC. The experimental results showed that the Fe metallization ratio (MFe/TFe) reached about 100 wt% above 1150 °C regardless of the reduction atmosphere. The maximum carbonization ratio of Ti (TiC/TTi) was 98.55 wt% after roasting at 1300 °C for 2.5 h in Ar atmosphere. The total carbonization and nitridation ratio (TiN/TTi) was 99.55 wt% when reduced at 1300 °C for 2.5 h in N2 atmosphere. The main Ti–bearing phases were reduced and carbonized in the order of ilmenite (FeTiO3)→ ferropseudobrookite (FeTi2O5)→ Fe,Ti,Mg Oxide (Fe0.33Ti0.46Mg0.21)(Ti1.9Mg0.1)O5→ titanium carbide (TiC). TiC was further nitrided to form TiN, which combined with TiC as titanium carbonitride (Ti(C,N)). TiC/TiN/Ti(C,N) granules, with a particle size less than 10 μm, were mainly dispersedly distributed in metallic iron. They also gathered at the edge of metallic iron and part of them existed in the the interval between metallic iron and gangue minerals.

Synergetic utilization of copper slag and ferruginous manganese ore via co-reduction followed by magnetic separation process

Attempts to economically and effectively treat copper slag (CS) and ferruginous manganese ore(FMO) using the traditional direct reduction–magnetic separation process have faced many challenges, such as low levels of metal recovery, poor cost-effectiveness and the need for a high proportion of additives. This paper proposes an eco-friendly process to synchronously utilise copper slag and ferruginous manganese ore by co-reduction followed by a magnetic-separation process to solve those problems. In the process, MnO2 within FMO acted as a catalyst to promote the reduction of fayalite and copper sulphide contained in CS, and thus improve the metallisation rate of Fe and Cu. Meanwhile, CS, possessing the low melting point, can enables more liquid phase generation and improve the growth of alloy particle, which is beneficial for the full liberation of Fe–Cu alloy. Under the optimum conditions, A crude Fe–Cu alloy powder containing 88.83% Fe and 1.07% Cu was prepared, which can be used in an electronic furnace to produce Cu-bearing steels. A high recovery of 85.89% Fe and 87.74% Cu can be obtained using this process, thereby confirming its efficiency. Additionally, Mn contained in the ferromanganese ore was enriched into the magnetic tailing in the form of low-valence manganese (II) oxides, which can be easily extracted by acid leaching. Moreover, the mechanism involved in the co-reduction of CS and FMO was investigated by XRD, SHTT and SEM-EDS techniques, which further confirmed the complementary advantages about an organic integration of CS and FMO can realise the efficient beneficiation of the valuable metals from them.

Preparation of a Master Fe–Cu Alloy by Smelting of a Cu-Bearing Direct Reduction Iron Powder

Generally, the Cu-bearing direct reduction iron powder (CBDRI) obtained from a direct reduction-magnetic separation process of waste copper slag contains a high content of impurities and cannot be directly used to produce Cu-bearing special steel. In this paper, further smelting treatment of CBDRI was conducted to remove its impurities (such as S, SiO2, Al2O3, CaO and MgO) and acquire a high-quality Fe–Cu master alloy. The results show that the Fe–Cu master alloy, assaying 95.9% Fe, 1.4% Cu and minor impurities, can be obtained from the smelting process at 1550 °C for 40 min with 1.0 basicity. Meanwhile, the corresponding iron and copper recoveries are 98.6% and 97.2%, respectively. Theoretical calculations and experimental results show that appropriate basicity (0.9~1.1) is beneficial for the recovery of Fe and Cu from a thermodynamic viewpoint due to the excellent fluidity of the slag in this basicity range. Moreover, the mechanism of desulfurization was revealed by calculating the sulfide capacity and the desulfurization reaction kinetics. Increasing the binary basicity of the slag benefits both the sulfide capacity and diffusion coefficient of the sulfur in the molten slag, resulting in higher desulfurization efficiency and lower S content in the master alloy.

A novel process to upgrade the copper slag by direct reduction-magnetic separation with the addition of Na2CO3 and CaO

An innovative technology for direct reduction-magnetic separation with the addition of Na2CO3 and CaO was studied to upgrade copper slag assaying 40.33% Fetotal and 0.65% Cu. It is difficult to recover iron and copper from the slag by direct reduction since the iron mainly occurs in fayalite and the copper exists in copper sulfide. Additives such as Na2CO3 and CaO has been proven to be capable of reinforcing the reduction of refractory iron ore in many papers. In this study, the effect of Na2CO3 dosage and binary basicity (CaO/SiO2) on the coal-based reduction of copper slag was investigated. The results show that the addition of CaO at 0.5 basicity and 8% sodium carbonate, the recovery of the iron and copper can be significantly improved to 94.3% and 86.5%, respectively. Meanwhile, the iron and copper content of magnetic concentrate are maintained at 90.5% and 1.2%, respectively, which can be used as burden for smelting of weathering steel, and the nonmagnetic tailings obtained in this process can be applied as raw materials in cement and industry, and the dust collected from the direct reduction process contains 50.65% Zn and 8.56% Pb at a recovery of 99.16% and 91.89%, and can be used as feed for extraction of Zn and Pb.

Zero-Waste Recycling Method for Nickel Leaching Residue by Direct Reduction–Magnetic Separation Process and Ceramsite Preparation

In this paper, a novel process for beneficiation of metallic iron from nickel leaching residue and preparation of ceramsite from tailings by direct reduction–magnetic separation process is reported. The optimal conditions for direct reduction process were 1100 °C roasting temperature, 120 min duration, and 30 wt.% reductant dosage. The reduced sample was benefited from low-intensity magnetic separation. This process yielded an iron concentrate of 82.32 wt.% grade and 78.05 wt.% recovery. Hence, this metallic iron could be used as a feedstock for the steel industry. Tailings of the magnetic separation procedure were used to prepare ceramsite. Optimal conditions for preparing ceramsite were: 55% magnetic separation tailings, 20% silica, 15% fly ash, 10% charcoal, a 1150 °C roasting temperature, and a holding time of 30 min. The ceramsite properties met the requirement of CJ/T299-2008 National Standard. These results suggested that developing this solid waste would have environmental and economic benefits.

Dephosphorization Behavior of High-Phosphorus Oolitic Hematite-Solid Waste Containing Carbon Briquettes during the Process of Direct Reduction-Magnetic Separation

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.

Modeling assessment of recovering iron from red mud by direct reduction: magnetic separation based on response surface methodology

Red mud, the waste generated during alumina production, contains iron and other valuable metals. To recover the iron efficiently from red mud, a three-factor five-level central composite design in response surface methodology was used to study the effects of process parameters, such as FC/O (the molar ratio of fixed carbon in coal to reducible oxygen of iron oxide in red mud), reduction temperature, reduction time, and their interaction on the iron recovery rate and total iron content in magnetic product obtained from the process of direct reduction–magnetic separation. The relevant assessment model was established. The model could predict the changing rules of iron recovery rate and total iron content in the magnetic product affected by the process parameters. The results show that the iron recovery rate is significantly influenced by three factors and reduction temperature plays the most important role. The iron recovery rate and total iron content in magnetic product could be up to 98.37 and 82.52%, respectively, under the numerically optimal process parameters condition of reduction temperature of 1400 °C, FC/O of 0.80 and reduction time of 100 min obtained by the assessment model. The predicted values are in good agreement with the experimental values.

Optimization and microstructure study of the reduction of nickel smelting slag mixed with calcium carbide slag and coke dust for recovering iron

How to treat more industrial solid waste friendly and environmental have become the global issues. In this study, direct reduction-magnetic separation (DRMS) process was employed to recovery iron from the nickel smelting slag (NSS) with calcium carbide slag (CCS) as the additive and coke dust (CD) as the reductant. Response surface methodology (RSM) approach using central composite design (CCD) was adopted for optimizing the effects of reduction temperature, reduction time and CCS dosage on the iron content of iron concentrate powder (ICP) and iron recovery. The results were modeled and the impact factors were evaluated. All the plots show that there were positive correlations between investigated impact factors and responses in a certain range but if exceeded, the positive correlations would be broken down. The overall optimization reaction conditions were converged as around 1287 oC, 2.8 h and CCS dosage of 57.19 %. Under these proven optimization reaction conditions, the iron content of ICP and iron recovery were reached up to 91.30 % and 95.44 % respectively. The micro phase of reduced samples were investigated by X-ray diffraction analysis (XRD), in reduction process, and the microstructure of reduced samples under the optimal condition were investigated by SEM for further discussion and analyzation. The experimental results and microstructure analysis suggests that utilizing CCS and CD in DRMS process were viable.

Effect of Na2CO3 Addition on Carbothermic Reduction of Copper Smelting Slag to Prepare Crude Fe-Cu Alloy

Copper smelting slag is a useful secondary resource containing high iron and copper, which can be utilized to prepare crude Fe-Cu alloy by a direct reduction–magnetic separation process for making weathering-resistant steel. However, it is difficult to recover iron and copper from the slag by direct reduction since the iron mainly occurs in fayalite and the copper is held in copper sulfide. Therefore, enhancement reduction of copper slag is conducted to improve the recovery of copper and iron. Additives such as Na2CO3 has been proven to be capable of reinforcing the reduction of refractory iron ore. In this research, the effect of Na2CO3 on the carbothermic reduction of copper slag was investigated, and phase transformations during reduction and the distributing characteristics of iron and copper in the alloy and non-metallic phases of the reduced pellets were also studied. The results show that the metallization rate of iron and copper was increased with the addition of Na2CO3, leading to higher iron and copper recovery in Fe-Cu alloy powder. X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) results confirm that Na2CO3 is capable of enhancing the reduction of fayaltie, copper silicate and copper sulfide, which agrees well with thermodynamic analysis. Furthermore, the reduction mechanism of copper slag was demonstrated based on systematic experimental observations.

Reaction Mechanism of Siderite Lump in Coal-Based Direct Reduction

AbstractSiderite is one of the significant iron ore resources in China and yet is difficult to upgrade by traditional beneficiation processes. A process of coal-based direct reduction–magnetic separation was successfully developed for the beneficiation of siderite. However, few studies have thoroughly investigated the mechanism of the direct reduction of siderite. In order to reveal the reaction mechanism of coal-based direct reduction of siderite lump, thermodynamics of direct reduction was investigated with coal as the reductant. The thermodynamics results indicate that coal-based direct reduction process of siderite lump at 1,050°C follows the steps as FeCO3→ Fe3O4→ FeO → Fe, which is verified by chemical titration analysis, X-ray diffraction and scanning electron microscope. The microstructure of siderite sample varies with different reduction stages and some 45% porosity induced by thermal decomposition of siderite is conductive to subsequent reduction. The conversion of FeO to Fe is the main reduction rate-controlling step. The reduced product with the metallic iron size over 30 μm can be effectively beneficiated by wet magnetic separation after grinding. The obvious layered structure of reduced product is due to different heat transfer resistance, CO and CO2 concentration.

Direct reduction and beneficiation of a refractory siderite lump

Siderite is refractory to beneficiate and is directly used as burden for ironmaking because of its high loss of ignition (LOI) and decompositions of carbonate. In this paper, mineralogy of a siderite lump was studied, a process of coal-based direct reduction-magnetic separation of the siderite lump sample was proposed and process parameters have been optimised. It is shown that the final sponge iron powder, assaying 92·40% of Fe and 92·28% of metallisation degree, was manufactured with iron recovery of 96·60% under the following conditions: reducing siderite lump sample with 40·62% Fe and the particle size between 8 and 10 mm at 1050°C for 100 min and carbon to iron ratio of 2·3. Followed by wet grinding of reduced sample to 80% passing 0·037 mm and magnetic separation with Davis tube at 0·1 T magnetic field intensity. The author proposed an effective way of using siderite ores as burdens for electric arc furnace to produce superior special steel.

Pilot scale test of producing nickel concentrate from low-grade saprolitic laterite by direct reduction-magnetic separation

The enrichment of Ni from a low-grade saprolitic laterite ore, which has been pre-treated by high pressure grinding roller(HPGR) to be 74% passing 0.074 mm and contains 0.92% Ni, 18.47% Fe, 10.61% MgO and 42.27% SiO2, was conducted by using pelletizing, rotary kiln reduction and magnetic separation process on a semi industrial scale, and the effects of reduction duration, mass ratio of coal to pellets(C/P), the types of magnetic separator, the sections of grinding-separation and the grinding fineness on the recovery of Ni and Fe were examined. It is shown that nickel concentrate containing 3.13 % Ni and 59.20 % Fe was achieved at recoveries of 84.36 % and 71.51 % for Ni and Fe, respectively under the following conditions: reducing at (1120±40) °C for 120 min, C/P being 1.0, wet grinding of reduced pellets up to 70%–87% passing 0.074 mm and a magnetic field intensity of 238.8 kA/m during the first section of grinding-magnetic separation, and a grinding fineness of 84%–91% passing 0.045 mm and a magnetic intensity of 39.8 kA/m during the second section of grinding-magnetic separation. The enriched Ni containing concentrate has a low content of S and P, and can be used for further processing to produce high-grade ferronickel alloy.