Fundamental Research On Recovery Of Valuable Components And Resource Utilization Of Steel Slag

With the rapid increase of china’s crude steel production, the output of steel slag has being increased in recent years. At present, the utilization ratio of steel slag is still low in China. Therefore, improving the comprehensive utilization level of the steel slag has important significant to the sustainable development of the steel industry in China.On the basis of comprehensively reviewing the development history of comprehensive utilization technology of steel slag, abundant research work was done in this thesis according to the composition and the phase characteristics of different steel slag, such as the reseach on beneficiation method of iron and magnetic separation of phase bearing Fe in steel slag, the research on recovery of iron and phosphorus from steel slag by smelting reduction, and the research on desulfuration of steel slag by oxidizing roasting. The main reseach results of this thesis were shown as follows under the given experimental conditions.(1) The main silicate phase was2CaOSi02in the BOF slag. The crystal shape of2CaO·SiO2was dendritic in quenching slag and was round in slow cooling slag. The value of nCO/nSiO2was2.1-2.4in the phase of2CaOSiO2. The element of phosphorus was beneficiated in2CaOSiO2with the phase of Ca2SiO4·0.05Ca3(PO4)2. Under the cooling condition of splashing or water quenching the iron oxides existed in the glass phase. Nevertheless the amount of solid solution of RO phase bearing Fe increased with the decrease of cooling rate. Hence, the iron was beneficiated in the RO phase in the dendritic shape as’+’ or the lamellar shape.(2) The grade and yield ratio of iron in magnetic concentrate increased with the decrease of cooling rate of BOF slag. By grinding the particle size of more than70%of the slowly cooling BOF slag was less than0.074mm. Then the magnetic concentrate was magnetic separated from the fine-grained slag at magnetic field intensity of0.16T. The grade of iron reached37.98%and the yield ratio of iron reached29.06%in magnetic concentrate.(3) When economical efficiency and dephosphorization effect were considered together, the relatively appropriate technological conditions of dephosphorization of steel slag by smelting reduction were shown as follows. The reductant was chosed as C-saturated molten iron. The slag was premelted using SiO2as modifier and then the basicity became1.0. W(T.Fe) of slag was12.88%and w(P2O5) of slag was1.54%. The temperature was1550℃and the mass ratio of slag and molten iron was1:2in the process of smelting reduction. Under the above-mentioned conditions, after smelting reduction more than once by cyclic utilizing C-saturated molten iron, MnO was reduced scarcely, and iron oxides and P2O5could be reducted compeletly.(4) The occurrence phase of sulphur in steel slag was CaS or Ca12Al14O32S. The phase of Ca12Al14O32S was formed by replacing CaO in the phase of12CaO·7Al2O3with CaS. A part of CaS could be oxidized to CaSO4by oxidizing roasting for60min under the atmosphere of oxygen volume fraction of21%at900℃. And then the reaction between CaSO4generated in the previous reaction and residual CaS could run by roasting for40min under argon atmosphere at1100℃. In this process desulfurization could be completed. Roasting the industrial slag bearing sulphur by the above-mentioned process, sulphur could be removed effectly with the desulfurization ratio of60%.The research results of the thesis played an important theoretical guiding role in the high value-added comprehensive utilization of steel slag.