| Chromite is main raw material for smelting ferrochromium。China is lack of chromite resources, We only have a 0.15 percent sliver of the pie in the world,95 percent of the chromite here is imported. China's 2008 chromite imports amounted to 6.84 million tons. The annual yield of chromite is about 20 million tons, which contains 80 percent of chromite fines.The chromite fines is cheaper,high-taste, but agglomeration is one necessary process to utilize. In order to decrease the producing cost and promote the market competitiveness of ferrochrome alloys, it is an effective way to use the cheap ore fines and improve the agglomeration of ore fines and concentrates to enhance the smelting. How to utilize the imported chromite concentrate to make good sintering quality, and then to smelt high carbon ferromanganese alloys was studied.The study used pellets sintering-electric furnace smelting process, which can gain high carbon ferrochrome alloys from chromite concentrate. The contents of this investigation include:the pretreating of ore fines and sintering, and parameters of reducing smelting processing, etc. The mechanism of the pretreating and the consolidation of fired manganese ore pellets were also investigated.The operation parameters of pellets sintering process are optimized as follows:7% coke breeze(30% of it added into pellet feed before balling),9.5% moisture,650mm bed height, drying at 300-350℃and 4kPa suction for 3min, ignition at 1100℃and 5 kPa suction for 1.5min, and sintering at 8 kPa, and excellent sintering index being attained as the following:unit productivity of 3.01t/m2.h, tumble index of 89.33%, and solid fuel consumption of 79.19 kg/t. Chromite sinter is difficult to reduce at 900℃due to chromium spinel occurring, and has high strength during reduction because of reduction swelling of 5-6% and RDI+3.15 over 94%.The solidification mechanism of pellets sintering was studied by using microscope,SEM.Results show that sintering of chromite consist of Fe-Cr spinel, Mg-Cr spinel, Mg-Al spinel and olivine.The agglomeration of sinter mainly depends on recrystallization of spinels and liquid phase of olivine plays an assistant role as well. Pellets have good structure and strengthen under 30% coke added into inside pellet and 70% coke adhered at the surface of pellet.Using sample A to make reduction smelting, the effect of reduction smelting temperature, time, slag basicity, MgO, Al2O3 etc. elements at the quality of ferrochromium is studied. It's shown that the temperature of smelting impart significant influence over the separation of metals from slag. High temperature can make the heat transferring strengthened, and it's profitable in melting and decreasing the slag viscosity. When reducing smelting pellets A at 1800℃for 15 min, high quality ferrochromium was produced. The basicity (CaO/SiO2) of slag highly affects, the proper basicity is 1.5. The proper MgO content can make the slag viscosity lower and get good slag fluidity. In the experiment,13% MgO content reaches good result. And the content of Al2O3 must keep at a certain value, 15% Al2O3 content can reach best result. The final chemistry analytical of the ferroalloy indicates that the grade of Cr is 53.76%, Fe is 31.57%, C is 10.04%, Si is 2.0%, P is 0.035%, and S is 0.046%, respectively, it can reach the quality standards of brands FeCr55C1000.
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