Deqing Zhu

Recovery of Iron From High-Iron Red Mud by Reduction Roasting With Adding Sodium Salt

Red mud is the waste generated during aluminum production from bauxite, containing lots of iron and other valuable metals. In order to recover iron from red mud, the technology of adding sodium carbonate—reduction roasting—magnetic separation to treat high-iron red mud was developed. The effects of sodium carbonate dosage, reduction temperature and reduction time on the qualities of final product and the phase transformations in reduction process were discussed in detail. The results showed that the final product (mass percent), assaying Fe of 90.87% and Al2O3 of 0.95% and metallization degree of 94.28% was obtained at an overall iron recovery of 95.76% under the following conditions of adding 8% sodium carbonate, reduction roasting at 1 050 °C for 80 min and finally magnetic separation of the reduced pellets by grinding up to 90% passing 0.074 mm at magnetic field intensity of 0. 08 T. The XRD (X-ray diffraction) results indicated that the iron oxides were transformed into metallic iron. Most of aluminum mineral and silica mineral reacted with sodium carbonate during the reduction roasting and formed nonmagnetic materials.

Upgrading and dephosphorization of Western Australian iron ore using reduction roasting by adding sodium carbonate

The technology of direct reduction by adding sodium carbonate (Na2CO3) and magnetic separation was developed to treat Western Australian high phosphorus iron ore. The iron ore and reduced product were investigated by optical microscopy and scanning electron microscopy. It is found that phosphorus exists within limonite in the form of solid solution, which cannot be removed through traditional ways. During reduction roasting, Na2CO3 reacts with gangue minerals (SiO2 and Al2O3), forming aluminum silicate-containing phosphorus and damaging the ore structure, which promotes the separation between iron and phosphorus during magnetic separation. Meanwhile, Na2CO3 also improves the growth of iron grains, increasing the iron grade and iron recovery. The iron concentrate, assaying 94.12wt% Fe and 0.07wt% P at the iron recovery of 96.83% and the dephosphorization rate of 74.08%, is obtained under the optimum conditions. The final product (metal iron powder) after briquetting can be used as the burden for steelmaking by an electric arc furnace to replace scrap steel.

Simultaneously Roasting and Magnetic Separation to Treat Low Grade Siderite and Hematite Ores

During the roasting process, siderite (FeCO3) transforms to magnetite (Fe3O4) along with producing carbon monoxide (CO), but hematite (Fe2O3) needs CO to reduce into magnetite. The process of simultaneously roasting and magnetic separation was developed to treat the low grade siderite and hematite ores without adding any reductant. Effect of mass ratio of S-to-H (siderite ore to hematite ore) on the separation indexes of iron concentrate was discussed. X-ray diffraction was also employed to detect the phase transformations of roasted ores. The technology of simultaneously roasting and magnetic separation is an effective way to treat low grade siderite and hematite ores, and also reduce the emission of CO2 because no ruductant is added.

Utilization of nickel slag using selective reduction followed by magnetic separation

In order to utilize slag discarded by nickel plants, the selective recovery of nickel and copper versus iron was investigated by selective reduction, which was achieved by controlling the reduction parameters and magnetic separation process on bench scale. The results show that increasing the basicity (mass ratio of CaO to SiO2) of nickel slag facilitates the enrichment of nickel and copper. The process parameters for selective reduction were optimized as follows: basicity of 0.15, reducing at 1200 °C for 20 min, 5% coal on a dried slag mass base. The grinding-magnetic separation results of reduced briquettes show that concentrate containing 3.25%Ni, 1.20%Cu and 75.26%Fe is obtained and selective enrichment is achieved with a recovery of 82.20%, 80.00% for nickel and copper respectively, while the recovery of iron is only 42.17%. The S and P contents are not reduced obviously and further research may be needed to examine the behaviors of S and P in the process.

Direct reduction and beneficiation of a refractory siderite lump

Abstract 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.

Influence of Mechanical Activation on Acid Leaching Dephosphorization of High-phosphorus Iron Ore Concentrates

High pressure roll grinding (HPRG) and ball milling were compared to investigate the influence of mechanical activation on the acid leaching dephosphorization of a high-phosphorus iron ore concentrate, which was manufactured through magnetizing roasting-magnetic separation of high-phosphorus oolitic iron ores. The results indicated that when high-phosphorus iron ore concentrates containing 54.92 mass% iron and 0.76 mass% phosphorus were directly processed through acid leaching, iron ore concentrates containing 55.74 mass% iron and 0.33 mass% phosphorus with an iron recovery of 84.64% and dephosphorization of 63.79% were obtained. When high-phosphorus iron ore concentrates activated by ball milling were processed by acid leaching, iron ore concentrates containing 56.03 mass% iron and 0.21 mass% phosphorus with an iron recovery of 85.65% and dephosphorization of 77.49% were obtained. Meanwhile, when high-phosphorus iron ore concentrates activated by HPRG were processed by acid leaching, iron ore concentrates containing 58.02 mass% iron and 0.10 mass% phosphorus were obtained, with the iron recovery reaching 88.42% and the dephosphorization rate reaching 88.99%. Mechanistic studies demonstrated that ball milling can reduce the particle size, demonstrating a prominent reunion phenomenon. In contrast, HPRG pretreatment contributes to the formation of more cracks within the particles and selective dissociation of iron and P bearing minerals, which can provide the favorable kinetic conditions to accelerate the solid-liquid reaction rate. As such, the crystal structure is destroyed and the surface energy of mineral particles is strengthened by mechanical activation, further strengthening the dephosphorization.

Oxidation and Induration Characteristics of Pellets Made from Western Australian Ultrafine Magnetite Concentrates and Its Utilization Strategy

Western Australian magnetite concentrates normally have ultrafine granularity and much higher specific surface areas than Chinese magnetite concentrates owing to the significant pre-grinding and beneficiation for saleable iron grade. Such characteristics will inevitably affect the subsequent pelletization process. However, very few investigations have been done before. Thus, the oxidation and induration characteristics of pellet made from a Western Australian ultrafine magnetite concentrate were revealed by conducting routine preheating-roasting tests in an electric tube furnace and investigating the microstructure of fired pellets under an optical microscope in comparison with that of pellets made from typical Chinese magnetite concentrate. The liquidus regions of CaO-SiO2–Fe2 O3 and CaO-SiO2–Al2O3 ternary systems in air at various temperatures were calculated by FactSage software to explain the importance of liquid phase in the consolidation of fired pellets. The results show that pellet made from ultrafine magnetite concentrate possesses better oxidability and preheating performance than that made from Chinese magnetite concentrate. However, it has inferior roasting performance, usually requiring conditions of roasting at 1280 °C for at least 30 min to acquire sufficiently high compressive strength, which are attributed to higher temperature sensitivity caused by its smaller particle size and less formation of liquid phase because of low impurities like CaO and Al2 O3 in raw materials. Correspondingly, its roasting performance can be significantly improved by blending with Chinese magnetite concentrates or increasing the pellet basicity (ωcao/ωsio2). By comprehensive evaluation, blending with Chinese iron ore concentrates is an appropriate way to utilize Western Australia ultrafine magnetite concentrates.

Improving the Pelletization of Chromite Concentrate by HPGR and Its Mechanism

A study of pelletization of one imported chromite concentrate with coarse site, poor ballability and refractory roasting performance was conducted in small scale tests, and high pressure grinding rollers (HPGR) was used to improve the pelletization. The mechanism of HPGR was revealed by means of SEM images and optical microscopy. Compared with the ball milling pretreatment, HPGR pretreatment can not only enhance the ballability of pellet feed but also drop the roasting temperature. Fired pellets, containing proper chemical compositions with high compressive strength of 2917N/pellet and good metallurgical performances, have been manufactured. The mechanism of HPGR reveals that chromite particle surface turns to more irregular after HPGR treatment and more new surface being formed because of more cracks, sharp corners and edges appearing, resulting in higher surface chemical activity, all of which improve the ballability of the chromite concentrate and contribute to the consolidation of fired pellets.

Utilization of High Sulfur Raw Materials in Iron Ore Pellets

Pyrite cinder and high sulfur magnetite were used as raw materials to produce iron ore pellets. Good qualities of green balls and fired pellets were obtained from the feed comprising 50% pyrite cinder and 50% high sulfur magnetite concentrate at a small scale. Small-scale tests were proven by pilot-scale tests. The high grade fired pellets, assaying 63. 22% Fe, were analyzed, and the compressive strength of fired pellets was over 2500 N/pellet. The fired pellets possessed excellent metallurgical performances, such as reducibility index higher than 67%, reduction swelling index lower than 15% and low temperature reduction degradation index (+ 3.15 mm) higher than 1%, which can be used as the burden for blast furnace.

Improving the Granulating and Sintering Performance by Pretreating Concentrates Using Extrusion Machine

In this paper, the pretreatment of concentrates by extrusion machine was present to improve the granulation of blends comprising some 30% iron ore concentrates and enhance the sintering performance. It is shown that by pretreatment of fine concentrates through extrusion machine, the content of +3mm fractions of granulation mixture and sinter mixture permeability are elevated by 10% and 35%, respectively. In the meantime, an increase in sinter productivity from 1.51 to 1.62t.m-2.h-1 is attainted in pot tests with similar sinter tumble index and at lower coke rate. The mechanism of the pretreatment of concentrates process to improve sintering performance of fine iron ore concentrates was demonstrated by mineralogy that better permeability help form more calcium ferrite and good microstructure of sinter, further proven by the better metallurgical performance of sinter.