Research On Pre-concentration And Deep Reduction Of Qidashan Iron Ore Tailings And The Comprehensive Utilization Of Tailings

The total iron content of Qidashan iron ore tailings is 12.54%.The iron phases is mainly in the form of magnetite and hematite,followed by magnetite.Due to the extremely fine dissemination size of iron minerals and its low single liberation degree,the recovery of iron and a high grade iron concentrate by physical processing methods is difficult.Therefore,a new technology(pre-concentration deep-reduction magnetic-separation technology)was developed to enhance the efficiency of iron recovery and resolve problems associated with storage of iron ore tailings.A pre-concentration method(primary high-intensity magnetic separation followed by the regrinding of rough concentrate and low-intensity magnetic separation and medium-intensity magnetic separation process)was used to pre-concentrate the iron ore tailings.A pre-concentrated concentrate achieved an iron grade of 36.58%and an iron recovery rate of 69.86%.Then two different direct-reduction methods including heating up with furnace and fast reduction under high temperation was used to obtain the reduced iron powder with an iron grade of>93.41%and an iron recovery rate of ?93.65%.And the concrete(C20-C60)was prepared from cementitious materials mixed with 10%fine tailings after pre-concentration or tailings after deep reduction.The tailings sand concrete was prepared by the optimum ratio of the pre-concentration of the +0.08mm part of tailings to manufactured sand is 8:2.Through this technology,the purpose of the comprehensive utilization of Qidashan iron ore tailings was achieved.The experiments of heating up with furnace showed that the temperature has the greatest influence on an iron grade of the reduced iron powder,and followed by the dosage of Na2CO3 and the dosage of CaO.The effect of these factors on the iron recovery rate of the reduced iron powder was negligible.The optimum process parameters were proposed as follows:weight ratios of pre-concentrated concentrate/bituminous coal/CaO/Na2CO3 at 100:17.5:15:4,heating up to 1300? at 10?/min and then roasting for 30 min.The experimental study of fast reduction under high temperation found that the iron grade of reduced iron powder increased from 89.52%to 93.98%(91.89%)by adding a small amount of Na2CO3(CaF2),and the roasting time was also reduced by 50%due to the addition of Na2CO3.The optimum process parameters were proposed as follows:weight ratios of pre-concentrated concentrate/bituminous coal/Ca(OH)2/Na2CO3 at100:17.5:20:0.6,roasting at 1325? for 20 min.The quantitative analysis of the iron content of ferrosilicate phase was performed and the generation and reduction mechanism of ferrosilicate phase was studied.The results showed that,due to the addition of 15%CaO and 4%Na2CO3,some wustite was involved in the formation of ferrosilicate phase.The reduction of ferrosilicate phase was occured at the phase interface between ferrosilicate phase and gas phase,and the internal Fe2+ migrated to the phase interface to reduce.The phase boundary between the metallic iron layer and the slags was distinct,which will be of great benefit to the subsequent grinding-magnetic separation and increasing the iron grade and iron recovery rate of reduced iron powder.The phase diagram calculation of thermodynamic software FactSage 7.1 and metallic iron particle size analysis showed that the liquid phase was rapidly generated in the early stage of high temperature reduction by adding 0.6%Na2CO3 or CaF2 and catalyzed the generation of ferrosilicate phase,reducing the melting point and the viscosity.As a result,the structure of the ore was destroyed,the migration of Fe2+and the diffusion of crystalline particles was accelerated,and advanced the growth of the metallic phase.The promotion of Na2CO3 on the growth of the metallic phase was more stronger than that of CaF2.