Xianlin Zhou

Thermal decomposition behaviour and kinetics of Xinjiang siderite ore

In order to provide a better theoretical foundation for utilisation of Xinjiang siderite resources in China, its thermal decomposition behaviour was studied in neutral and oxidising atmospheres by employing thermodynamics analysis, chemical titration, thermogravimetric, and X-ray diffraction means. Isothermal experiments were conducted to investigate the thermal decomposition kinetics of siderite lump in a weakly oxidising atmosphere at 500–850°C. The results reveal that siderite has self-magnetisation characteristics under controlled conditions, and the phase evolution process and final products of decomposition depend temperature and atmosphere. The phase transformation process in weak oxidising atmosphere follows the steps as: FeCO3 → Fe3O4 → γ-Fe2O3 at 550°C, and FeCO3 → FeO + Fe3O4 → Fe3O4 → γ-Fe2O3 → α-Fe2O3 at 800°C. In inert atmosphere, the decomposition pathway is FeCO3 → Fe3O4 below 733°C and FeCO3 → FeO + Fe3O4 above 733°C. The molar ratio of FeO/Fe3O4 increases with temperature. The decomposition kinetics of siderite lump in oxygen-deficient atmosphere is consistent with chemical reaction control in the temperature range 500–700°C and nucleation and growth mechanism in the 750–850°C. The corresponding activation energies are 53·73 and 38·15 KJ mol−1, respectively.

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.

Granulation behaviour of specularite fines in ferrous sinter mixtures

The granulation behaviour of specularite fines which possess poor ballability was studied with limonite fines as a function of nuclei particles and adhering fines. The results show that the permeability of granules deteriorated as the ratio of specularite fines increased in the mixture, and the optimal granulation moisture content also decreased. The granulation kinetics results demonstrate that the adhering load of specularite fines increased rapidly within 3 minutes and then levelled off. With increasing specularite fines ratio, the adhering rate accelerated but the granulation duration needed to be longer to reach adhering balance. The microstructure of granule quasi-particles indicates that the fine limonite particles act as binders to bond together the specularite particles which are dispersed in the adhering layers. This can improve the adhering strength of the granules. Hence, the granulation behaviour of specularite fines can be improved by blending them with fine limonite ores which have high adhering capabilities.

Utilisation of semi-coke as by-product derived from coal-based direct reduction process in iron ore sintering

Solid wastes derived from metallurgical industries have created threats to the environment and their disposal is a major concern for the World. Semi-coke generated in the coal-based direct reduction process of iron ore is a solid waste and its effective utilisation has not been developed so far. In order to develop it properly, the characteristics of this semi-coke have been comprehensively studied and an investigation was carried out into the use of semi-coke as an alternative fuel in iron ore sintering. It is shown that the semi-coke could be substituted for coke breeze without affecting the sintering and metallurgical performances by adjusting its size distribution to offset the adverse effect of its superior combustion properties. In addition, the application of semi-coke in sintering could decrease SOx and NOx pollutants by 66 and 25%, respectively, in waste gas compared with coke breeze as solid fuel.

Reaction Mechanism of Siderite Lump in Coal-Based Direct Reduction

Abstract Siderite 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.

‘One step’ technology to separate copper, zinc, lead from iron in metallurgical slag and pyrite cinder Part 1 – Laboratory scale test

Abstract In this paper, a study of processing pyrite cinder and metallurgical slag using a ‘one step’ technology in strand grate–rotary kiln at a laboratory scale is presented, which aims to recover iron, lead, zinc and copper. The compressive strength of preheated pellets reached 527 N per pellet and the removal rates of copper, lead and zinc reached 36·36, 92·86 and 20·0% respectively, when the green balls were preheated at 1125°C for 10 min. Reduction of preheated pellets was followed, at the carbon/iron ratio of 3·0 and 1100°C, for the reduction time of 70 min, and the metallisation degree of 86·31%, the compressive strength of 1777 N per pellet and the copper, lead and zinc removal rates of 36·36, 99·12 and 71·00% were achieved respectively. These prereduced pellets with 80·58%Fe made from pyrite cinder and metallurgical slag can be widely applied to enhance the operation of blast furnace.

Theoretical Studies of the Emission Rule of SO2 and NOx in Iron Ore Sintering

Theoretical studies of the emission rule of SO2 and NOx during iron ore sintering was conducted, it is put forward that the emission of SO2 possesses the characteristics of self-sustaining which means the emission of SO2 rises to a peak value rapidly just before the sintering end point and then declines dramatically no matter how parameters of sinter technology and the properties of raw material change. It is also revealed that emission of NOx in sintering flue gas is originated primarily from the combustion of gas fuel during ignition and solid fuel in sintering bed. Compared with the emission rule of SO2 during sintering, the emission rule of NOx is quite different. From the finish of ignition to the end of sintering, the concentration of NOx in the flue gas always maintaines at a high level.

Monitoring the Ring Formation in Rotary Kiln for Pellet Firing

The grate-kiln process has been widely applied for oxide pellet production with the quick development of steel industry in China, but ring formation takes place which adversely affects the productivity and properties of fired pellets. Rotary kiln at high temperature seems a black box, and ring formation is difficult to measure directly by current technology. It’s of great importance to monitor ring formation during firing of pellets. Therefore, a method for estimating the thickness of ring formation in rotary kilns was studied, based on working out theoretically the relationship between ring thickness and the outside surface of the kiln, according to steady-state heat transfer across a cylinder, which provides a soft-sensing technique for ring formation at high temperature, and achieves stable pellet production.