| Meishan Iron Ore, the annual design production capacity of which is 4,000,000 tons, is a large-scale underground mine in China. However, with the increase of excavation depth, the content of magnetic ore decreased, and the proportion of hematite and siderite increased, which result in declining in iron concentrate grade, iron recovery and iron concentrate alkalinity, from self-fluxing into semi-self-fluxing. Iron concentrate of Meishan will face stern tests from iron ore market and rising pressure of beneficiation ratio as a result of Concentration-ratio ascent. Therefore, it is particularly important to improve the separation efficiency and economic benefits of Meishan Iron by adapting reasonable and effective process.The mineralogy characteristic of the complex and refractory iron ore of Meishan was systematically studied in this paper. On the basis, magnetic roasting studies of the feed of mill, tests of high intensity magnetic separation and step-by-step flotation for tailings from high intensity magnetic separation and reduction experiments of the concentrate from reconcentrating of tailings were conducted. The mechanism of magnetic-roasting process and reduction technique were also discussed in this paper.Magnetic roasting of the feeding ore of mill with different grain sizes was executed and influences on the process of types of reducing agent, amount of the reducing agent, calcination time, calcination temperature and the cooling mode were researched. When the reducing agent was coal gas, experiment studies showed that the indexes of iron concentrate received on the optimal experimental conditions with cooling down in water were grade 63.98%～66.68% and recovery 80.28%～89.60% and that cooled down under natural conditions were grade 61.93%～64.23% and recovery 82.43%～88.94%.Magnetite, hematite, siderite, quartz, ankerite, garnet, fluorapatite were contained in the field tailings of high intensity magnetic separation. Flotation experiments of the seven kinds of pure minerals had shown that the sodium oleate had good collecting property on the pure minerals above except quartz under the natural pH conditions, and single activator or inhibitor could not separate the seven kinds of minerals selectively, and inhibitors of combing the starch and CaCl2 had significantly different collecting property on the minerals above under different pH conditions. The indexes of regrinding the tailings from high intensity magnetic separation were Fe grade 37.71% and recovery 17.15% adapting high intensity magnetic separation and reverse flotation, and that of open circuit conditions were Fe grade 45.22% and recovery 37.12% adapting high intensity magnetic separation and flotation step-by-step.Reduction-magnetic separation experiments of the concentrate from reconcentrating of tailings showed that the effects of reducing temperature, reducing time, carbon additive, thickness of reducing material had important infullence on the metallization rate of reduced materials and particle size of coal powder had less impact on that. The optimum conditions for reduction determined by experiments were that reducing temperature was 1275℃, reducing time was 60 min, thickness of the materials was 30mm, carbon additive was 2, the particle size of coal powder was 2mm and the particle size of hematite was 2mm. Reduced materials with metallization rate 89.20% were obtained under this condition. The reduced materials was separated by process "pre-concentration-grinding-screening-magnetic separation-grinding-magnetic separation" and iron products (particle size -0.3mm) and ferrite (grain size +0.3mm) were obtained with total Fe grade 91.27% and Fe recovery of 91.55% when the fineness of twice grinding were 45% and 75%, respectively.Analysis was executed on the products from magnetic roasting of the feeding ore of mill. Calcined products were mainly Fe2O3, Fe3O4 and SiO2 when calcination temperature was 500 ℃ and 600℃, that were mainly Fe3O4, FeO and SiO2 when calcination temperature was 700 ℃ and 800℃ and that were mainly FeO, Fe and SiO2 when calcination temperature was 900 ℃ with coal gas as reducing medium.Analysis was executed on the processes of reduction. It showed that the iron minerals were reduced in the sequence of Fe2O3â†'Fe3O4â†'FeOâ†'Fe. The main reaction was the indirect reaction between carbon and iron oxide, with iron being generated in short time. The iron particles with irregular shapes were precipitated from the gangue matrix and grew up by the way of aggregation to large particles from small particles in the process. Part of the phosphate material was reduced to P, part of the sulfur mineral was transformed into CaS, FeS, CS2 and COS under the optimum conditions for reduction. And 35.91% of the phosphorus and 20.45% of the sulfur entered into the iron powder,45.06% of the phosphorus and 6.78% of sulfur evaporated with the CO gas flow, and the remaining 19.03% phosphorus and 72.77% sulfur were still exsiting as the phosphate or sulfate in the tailings. The content of harmful elements, such as P and S, were 0.37% and 0.48% in the last products of iron, respectively.The research in this paper provides a new technique method for improving the utilization efficiency of weakly magnetic minerals in Meishan Iron Ore and lays a theoretical foundation for its practical application. |
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