Hongming Long

Preparation of Chromium-iron Metal Powder from Chromium Slag by Reduction Roasting and Magnetic Separation

Chromium slag (CS) has become one of the most hazardous solid waste containing chromium and iron. Based on its characteristics, the technology of reduction roasting and magnetic separation was employed to treat CS. The major impurity element of CS is magnesium and it exists in magnesium ferrite phase, which is hard to recover iron in the absence of additives. During reduction roasting, additives (Al2O3 and CaF2) could destroy the structure of magnesium ferrite and improve the iron grade and recovery. The final product, i. e. chromium-iron powder, contains 72.54% Fe and 13.56% Cr, with the iron recovery of 80.34% and chromium recovery of 80.70%.

Emission reduction of dioxin in iron ore sintering by adding urea as inhibitor

Abstract Dioxins are a type of highly toxic persistent organic pollutant, and the sintering process has become one of the most important emission sources. In this paper, a detailed analysis of the waste gas from sintering pot experiments shows that when adding urea at 0·05, 0·1 and 0·5%, the dioxin emissions decrease by 63·1, 66·8 and 72·1% compared to zero urea. At 0·05%, the influence on the technical parameters of the sintering process is slight, and there is no emission of ammonia in the waste gas. However, at 0·1 and 0·5%, the sintering technical performance decreased and emissions of ammonia in flue gas at 0·07 and 0·11 mg m−3 occurred. It is concluded that an addition of 0·05% urea is the optimum amount to minimise dioxin without affecting sintering performance or the occurrence of secondary ammonia pollution.

Reduction kinetics of carbon containing pellets made from metallurgical dust

Abstract Reduction experiments of carbon containing pellets made from metallurgical dust were conducted under a weak oxidising atmosphere in the temperature range of 1348–1573 K. Analysis of kinetics and the reduction mechanism revealed that the rate determining step of the reduction of the pellets is the interfacial or local reaction with the activation energy 111·66 kJ mol−1. The reduction rate can be expressed by the McKewan equation 1−(1−R)1/3 = kt. In addition, temperature is an important factor influencing the reaction rate as dezincification and metallisation increase with the increased temperature. The amount of dezincification and metallisation could be up to 97·8 and 79·9% respectively at 1573 K compared to a minimum of 75·3 and 60·2% at 1348 K.

Alumina-Iron Separation of High Alumina Iron Ore by Carbothermic Reduction and Magnetic Separation

The carbothermic reduction of high alumina iron ore in the absence/presence of sodium carbonate (Na2CO3) was carried out for alumina-iron separation by wet magnetic separation. Sodium carbonate is found to be capable of improving the separation of alumina and iron, as well as increasing the particle size of metallic iron significantly. When the high alumina ore briquettes were reduced at 1050°C for 80 min, the average particle size of metallic iron was approximately 100 μm in the presence of sodium carbonate, which is bigger than the size of 50 μm in the absence of sodium carbonate. Compared with the absence of sodium carbonate, the Al2O3 content of iron concentrate decreased from 4.33% to 1.29%, while the Al2O3 removal rate increased from 43.70% to 83.37% with the addition of 9% sodium carbonate. Experimental evidence showed that Na2CO3 reacted with Al2O3 and SiO2 to form sodium silicate, aluminum silicate, and sodium aluminosilicate, and decreased the content of Fe in the slags, which improved the separation between the alumina and iron during the magnetic separation. Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lsst.

Influence of microwave heating on the microstructures of iron ore pellets with coal during reduction

Iron ore oxidised pellets as the burden of blast furnace present many advantages, such as uniform size, high iron grade and high physical strength. A comparison of the iron ore oxidised pellets with coal (out-proportioning) by conventional heating and microwave heating was carried out in this paper. Microstructure transformations during reduction process were investigated by optical microscopy and scanning electron microscope with energy dispersive spectrometry analysis. Micro-hardness of metallic iron phase formed in the reduction was tested with digital micro-hardness tester. The influences of microwave heating on reduction degree, morphology, iron phase and gangues were investigated, respectively. The results show that reduction time can be greatly shortened by microwave heating even at lower temperatures. The fine cracks generated, as the pellets were heated by microwave, were irradiated due to the selectivity of microwave heating. Densification of the metallic iron phase and the separation of the iron and gangues were both found to be enhanced by microwave heating.

Mechanism of Selective Desulphurization in Iron Ore Sintering Process by Adding Urea

Abstract Iron ore sintering is an important part during the ironmaking process, and a large amount of SO2 is also generated. Our previous research shows that it is an effective way to reduce SO2 content of flue gas by adding urea to a special sintering material zone position. In this paper, the mechanism of selective desulphurization by adding urea during the iron ore sintering was carried out. The results show that 88.14 % desulphurization rate was obtained with the addition of 0.05 % urea particles at 100 mm height from the feed bottom. During the sintering process, when drying zone reached the added position of urea, large amounts of NH3 were generated by urea decomposition, and then reacted with SO2 to produce (NH4)2SO4 in the wetting zone. With the accumulated desulphurization reactions during the sintering, the low SO2 emission in the flue gas was achieved. Moreover, the addition of urea in the bottom zone avoided the ammonia present in the sintering ore and promoted the urea utilization efficiency.

Assimilation Behavior of Calcium Ferrite and Calcium Diferrite with Sintered Al2O3 and MgO

In this study, the assimilation behaviors between calcium ferrite (CF), calcium diferrite (CF2) and sintered Al2O3, and MgO were explored by an improved sessile drop technique, and the interfacial microstructure was discussed. The results indicated that the apparent contact angles of CF slag on Al2O3 and MgO substrate were 15.7 and 5.5 deg, and the apparent contact angles of CF2 slag on Al2O3 and MgO substrate were 17.9 and 7.2 deg, respectively. Namely, CF and CF2 slag were wetting well with Al2O3 and MgO substrate. The dissolution of Al2O3 substrate into the CF and CF2 slag was found to be the driving force of the wetting process. For the CF-MgO and CF2-MgO substrate systems, CaO contrarily distributed with MgO after wetting. For the CF-MgO system, after wetting, the slag was composed of CF and C2F, and most of the Fe2O3 permeated into substrate and formed two permeating layers.

Control guidance system for sintering burn through point

Abstract Based on the characteristics of the sintering process, a long and short term control strategy of sintering burn through point was put forward, with the burn through point optimised with a fuzzy controller. Long term control was realised by adjusting bed height or density according to the state of preignition permeability and vertical sintering speed. The rising position of gas temperature was stabilised by adjustment of pallet speed, enabling short term control to be carried out. By using vertical sintering speed to represent bed permeability a prediction model of vertical sintering speed was established. The predicted results are in accordance with calculated values and accuracy of the model is >95%. The application of system shows that the accuracy of guidance is >95% and this system can be used to industry production.

A pilot-scale study of selective desulfurization via urea addition in iron ore sintering

The iron ore sintering process is the main source of SO2 emissions in the iron and steel industry. In our previous research, we proposed a novel technology for reducing SO2 emissions in the flue gas in the iron ore sintering process by adding urea at a given distance from the sintering grate bar. In this paper, a pilot-scale experiment was carried out in a commercial sintering plant. The results showed that, compared to the SO2 concentration in flue gas without urea addition, the SO2 concentration decreased substantially from 694.2 to 108.0 mg/m3 when 0.10wt% urea was added. NH3 decomposed by urea reacted with SO2 to produce (NH4)2SO4, decreasing the SO2 concentration in the flue gas.

Mathematical simulation and experimental study on coke oven gas injection aimed to low carbon blast furnace ironmaking

Coke oven gas (COG) tuyere injection is recognised as one of effective measures to achieve low carbon blast furnace ironmaking. In this paper, simulation of blast furnace operation with COG injection was investigated by means of multi-fluid blast furnace model, and the softening-melting and dripping behaviours of mixed burden were studied on basis of simulation results. The model simulation shows that, with COG injection rate increasing, the concentration of inner-furnace hydrogen is enhanced obviously. Cohesive zone moves downwards and becomes thinner. The column permeability gets better. Hot metal productivity increases and CO2 emission reduces. Compared with conventional operation without COG injection, when COG injection rate is 152.34 Nm3/tHM, column pressure drop is decreased by 31.5% and hot metal productivity is increased by 26.36% and CO2 emission is decreased by 17.54%. Therefore, the simulation and experimental results reveal that it is achievable to improve blast furnace operation performance, such as hydrogen-enriched reduction, better column permeability, high efficiency, low carbon emission and so on.