| Because of clarifying the separation of the oxygen-enriched top-blown bath smelting slag and low nickel matte in settlement furnace, the nickel metal content ex-ceeded the requirements of economic indicators in granulated slag. In order to resolve this difficulty, the author embraces the method of the nickel smelting slag-type con-taining nickel optimization to improve the properties of slag and decrease the loss of nickel metal in granulated slag.The objective of this dissertation to nickel smelting slag as the research goals:(1)To determine the principal occurrence state and path loss of nickel metal in slag through to the physical photograph and mineral topography by XRD and SEM-EDS investigates.(2)Without changing the slag components, based on original smelting slag as in-gredients mother slag. To determine the melting point temperature and viscosity of newly synthesized melting slag through four experiments processes of calculation, preparation, melting, detection and so on.(3)The best settlement conditions can be obtained through reasonable residence time of nickel smelting slag in settlement furnace calculation and evaluation by the formula of Stokes settlement. Including the temperature, viscosity and specific gravity of the slag, the specific gravity and particle diameters size of nickel matte.(4) Using the FactSage thermodynamic calculation software, combination of the-oretical and experimental data on the multi-phase and multicomponent equilibrium and phase diagram calculations to determine the mass of liquid phase of theory slag, sof-tening temperature, fluidization temperature. Meanwhile, research on the quadruple phase diagram of SiO2-CaO-FeO-MgO is analyzed. According to the different phase areas effect of the flux of FeO, MgO, CaO in the slag system phase. Eventually, the author determines theory slag-type approximate range at a temperature of around1300and e value of the oxygen partial pressure in slag.(5) In order to optimize the processing of data outside the experiments of slag-type, the author employs the method of kriging interpolation in statistics. Com- bined with the phase diagram of the theory of slag-type, and ultimately determine the scope of the reasonable type of slag in the production.The main conclusions of this paper are as follows:(1)The XRD and SEM-EDS analysis results show that the hortonolite (Fe, Mg)2SiO4is the dominance in system slag. Then there is a small amount of wollaston-ite (CaSiO3) and spinel (MgFe2O4, CoFe2O4). The copper, nickel, cobalt exists in the form of CuFeS2, Ni3S2, CoFe2O4respectively. The topography analysis results indicat-ed that a mass of the white low nickel mattes were distributed in system slag, and its existing form of a massive inclusions in the between pores and slag layer or attached pores around. The mechanic inclusion was play an important role in nickel losses in system slag accounted for approximately84.7%,then chemical dissolution and physical losses of around15.3%.(2)The melting point and viscosity test of synthetic slag-type results show that the original slag has a high melting point(nickel smelting slag and settlement slag, respec-tively1350℃and1320℃) and when the slag melting point temperature is smaller than1300℃, the original slag has a large viscosity. The nickel smelting slag(2.58～3.52Pa.s) and settlement slag(2.79～3.48Pa.s). With slag-type adjustment, the author found that the decreasing melting point of slag with increases CaO(2%～10%and18%～24%),the lowest melting point will be1257℃and1200℃respectively. Conse-quently, the fresh slag-type improves the fluidity of the slag and meets the require-ments of synthetic slag viscosity.(3)After doing the reasonable residence time of nickel smelting slag in settlement furnace analysis with the settlement of the Stokes formula expression, the author con-cluded that the factors that influence the separation efficiency of slag-matte are the slag viscosity and the size of the nickel matte particle diameter. There was a direct relation-ship between the properties of the slag and the separation efficiency of slag-matte. The residence time of smelting furnace slag in settling furnace is unreasonable and more than3.07h. Based on the collected data, through the theoretic calculation, the author concludes that the optimized condition of the slag-matte separation is the slag temper-ature control for the1350～1400℃,the viscosity of0.142～0.58Pa.s, the specific gravity of nickel matte and slag, respectively4.98～5.26t/m3and3.44～3.75t/m3, nickel matte particle diameter is129.38～200microns, then the clear separation time of slag-matte is only0.5～1.0h, namely the reasonable residence time of slag in set-tlement furnace.(4) Using thermodynamics software FactSage to calculate for the slag multivariate multiphase equilibrium and phase diagram. The results of this research proved that the mass of liquid phase of slag increased with increasing CaO content (0～20%). But when the CaO content is25%, the mass of liquid phase of slag instead of reduced. This was due to the excess CaO in slag, consequently the formation of a solid solution is (Ca,Fe,Mg)O. The calculated theoretical values for the softening temperature and flu-idization temperature are in agreement with the measured data of new synthetic slag-type. The results show that the MgO has a great influence on melting temperature in slag system. When MgO content surpasses12.75%, the melting temperature will increase sharply. Even if extra CaO that the temperature of the system would not re-duce, which related to the nature of MgO itself.(5)Based on an amount of experimental data, the article calculates and draws the SiO2-CaO-FeO-MgO system of the four ternary phase diagram as theory combined with practice. From this phase diagram, the author can determine that the best of slag-type at temperature below1300℃is as follows:FeO33.44～40%,SiO228.2～51.34%, MgO0～12.75%, CaO13.20～20%. But combining with kriging mathemati-cal interpolation method, the author considers the optimization results data of the actual slag-type and furnace operation conditions, which eventually resulted the composi-tion of the slag is CaO5～6%, FeO31.35～31.59%,SiO230.94～.32%,MgO12%,Fe3O48%,other impurities content11.71～.85%, the ration of Fe and SiO2is1.0, then the softening temperature of slag could be reduce to1178～1238℃,the melt-ing point temperature is1275～1293℃and fluidization temperature is about1330～1388℃According to the phase distribution and the relationship between the oxygen partial pressure of the phase diagrams. The SEM-EDS scanning atlas indicated that the white low-nickel matte particles were largely reduced in new synthesis smelting slag; only a small amount of low-nickel matte was dispersed and mingled with the slag layer. But the pores around was not attached, then the slag surface layer becomes incredibly dense. Therefore, after optimization of the slag-type is to achieve a higher enrichment of nickel matte, reduces the loss of nickel and copper mechanic inclusions. Compared with the original settlement slag containing nickel, the nickel content was approxi-mately0.33%and decreased by19.5%in fresh slag-type.In summary, the author had a certain understanding of the basic properties of the oxygen-enriched top-blown bath smelting slag. At the same time, the main suggestion and measures of reducing slag containing nickel were proposed, and it can help the clear separation effect of slag-matte in sedimentation furnace and effectually raised the recoveries rate of metal and economic benefits in nickel smelting production process. |
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