Phase Equilibrium Study And The Determination Of Liquidus Of The FeO_x-SiO₂-Al₂O₃-?CrO_x?-?CaO? Slag System

As a typical representative of "City Mine", electronic waste is more valuable than natural mineral resource. Smelting of electronic wastes by Pyrometallurgy processes is one of the most important terminal processing technologies. Due to the different of the composition and the mode of Storage ways between electronic wastes and natural mineral resources, the selection and control of slag system becomes the key. And it is important to comprehensively evaluate the effect of slag composition on slag property in electronic wastes.Based on previous research results, FeO_x-Al₂O₃-SiO₂-?Cr₂O₃?-?CaO?multivariate slag system was used as the main research object in this study.The slag properties study and phase equilibria study were carried out by the high temperature equilibrium—water quenching—Electron Probe Microanalysis ?EPMA? technology and dynamic high temperature observation technology ?hemispherical temperature method?, and the following conclusions were obtained:?1? In order to determine the time required to achieve the thermodynamic equilibrium during smelting process, the equilibrium time experiments of eight groups of different smelting time were carried out, and the equilibrium time was finally determined by 20 hours.?2? In this study, the liquid phase zone of the slag was measured and calibrated under the condition of temperature T= 1300 ? and oxygen partial pressure PO₂=10-8 atm, in the FeO-SiO₂-Al₂O₃ slag system. Finally, on the basis of the ternary phase diagram plotted by Factsage, a liquid phase zone graph is obtained. And it was found in the liquid phase zone graph that the actual liquid zone has a tendency to move to the high silicon region compared with the theoretical liquid phase zone plotted by Factsage.?3? The influence of Cr₂O₃ content changes under different conditions on melting temperature of FeO-SiO₂-Al₂O₃ slag system was investigated by hemispherical temperature method.With the addition of the 8wt% CaO,it can be found that the melting temperature increased first and then decreased with the increase of the content of chromium oxide. The melting temperature of low alumina slag decreased first and then increased with the increase of chromium oxide content in the slag, and the melting temperature of high alumina slag increased first and then maintained unchanged with the increase of chromium oxide content in slag.?4? The effects of temperature, oxygen partial pressure and the addition of CaO on the solubility of CrO_x in the glass phase of the slag were studied, and the solubility of CrO_x in glass phase was increased with the decreasing of oxygen pressure and the increasing of temperature. The solubility of CrO_x in the glass phase is increased from 0.505 wt% to 1.028 wt% when oxygen partial pressure changes from 1×10-6 atm to 1×10-9 atm. When melting temperature rises from 1200? to 1500?, the solubility of CrO_x in glass phase of molten slag increased from 0.655 wt% to 2.099 wt%. The addition of CaO has no obvious effect on the solubility of CrO_x in glass phase. In addition, the solubility of CrO_x in the glass phase increases with the increase of bulk CrO_x content in the slag. When the bulk CrO_x content is changed from 1 wt% to 6 wt%, the solubility of CrO_x in glass phase of molten slag increased from 0.046 wt% to 0.655 wt%.?5? The chemical state of Fe and Cr in two kinds of slag systems was investigated by X-ray photoelectron spectroscopy ?XPS?. The iron element in FeO-SiO₂-Al₂O₃ ternary slag system coexist mainly in the form of Fe2+ and Fe3,and the proportion of Fe2+ and Fe3+ in melt slag is [Fe2+]/[Fe3+]=0.0975. The existence morphology of Fe and Cr in Multicomponent slag system is Fe2+, Fe3+ and Cr2+, Cr3+respectively, and their proportion is respectively [Fe2+]/[Fe3+] = 0.183,[Cr2+]/[Cr3+]=0.9747.