Microwave Reduction Technology And Comprehensive Utilization Of Slag

Slag is mixture oxides formed by elements of steel making raw materials oxidized and solid dissolved with each other in steel furnaces. China is considered as the largest steel production country in the world, how to recycle efficient ingredients in steel slag will be a great significance problem in Chinese economic development. In this study, basic oxygen furnace?BOF? slag provided by Ningxia Steel making company as raw materials, carbon black and high carbon content fly ash as reducing agents,the BOF slag was reduced by microwave heating to recycle iron. Reduced product was separated by wet weak magnetic separation process; magnetic substance can be used to steel-making raw materials. Magnetic tailings were used to make slag cement. In this way, a new route to recycling the BOF slag was developed under the concept of “treating waste with waste”. The following three works had been done in this paper.First, BOF slag were broken by jaw crusher and were separated by dry magnetic separation process. The magnetic tailing was used as raw material in this study. The composite and phase of raw slags were analyzed by chemical analysis and X-ray diffraction?XRD?. The results showed that the main chemicals composition of slag were CaO, SiO₂, FeO, Fe₂O₃, MgO etc. The main mineral phases were dicalcium silicate?C2S?, tricalcium silicate?C3S? and Ca2Fe2O5. The total iron content of slags went up to 23.30%?credited with Fe₂O₃?, including Ca2Fe2O5, MgFe2O4, the oxidation state?FeO, Fe₂O₃, Fe3O4? and small amount of elemental iron. The Rietveld whole pattern fitting results showed that the content of cementinious phases including?-C2 S, C3 S, ?'-C2 S in slag reached 61.1%. The high content of cementinious phases was benefit to prepare cement. The thermal dynamic of reducing react between slag and carbon were calculated by Factsage6.4 thermodynamic software. The results showed that when t> 602.3?, Fe₂O₃ was first reduced to iron. All ferrous phases in slag could be reduced until t> 771.4 ?.Second, according to thermodynamic calculated results,the effective of different reducing agents, the reaction temperature, holding time and the carbon content on reduction of slag were studied. The results showed that metallization rate was up to 88.28% using carbon black as reducing agent when reaction temperature was 850?, holding time was 30 min, carbon black content was 4% respectively. When the high-carbon fly ash had been used as reducing agent, the effect of reducing temperature and holding time were similar with the results of carbon black as reducing agent. Based on the optimization process, metallization rate was reach to 89.56%. Reduced products were analyzed by ESM, the result showed that elemental irons distributed in reduced products dispersively, the maximum diameter of iron particle was up to 30?m and EDS results showed that the purity of the iron particles was relative high.Third, reduced products were separated by wet magnetic separation process. The result showed that reduced products of two reducing agents got the best separated results under the condition of magnetic field was 0.074 T. The grade of magnetic iron reached 66.79%, 64.82% respectively, and recovery rate reached 55.31%, 52.82%, respectively. Magnetic tailings were studied for preparing slag cement. The final setting time, stability and mortar strength of slag cement were measured. Results showed that their stability were qualified under slag content within 50%. The final setting time of slag cement was significantly longer, when the amount of slag exceeded 30%. The mortar strength of slag cement was measured under 30wt%, slag and 10wt% fly ash. The bending strength and compressive strength of mortars were measured to 6.22 MPa, 33.62 MPa, respectively, which reached intensity index of 32.5.cement.