Search

It has become a general developing trend to resource recyciing lead-contammg soiid waste,such as lead-silver leaching residues by kad smelting. However, due to the obvious difference of raw material structure, the conventional direct reduction control theory of ligh--ead slag is not suitable for that of the mixed lead-si1ver eaching resddues and lead concentrates. To investigate the stag formation characteristics and reaction kinetics of the direct reduction process for recyciing lead-si1ver stag leaching resddues^n the basss of the occurrence state analysis of raw materiais and thermodynamic caiculation, combined subsequent reduction experiment.. The resuits show that both the early and kte stages of reduction (>30 min) are controled by interfacia1 reactions, and the 20 -- 30 min of reduction controled by external diffuson. Therefore, the reduction reaction efficiency can be enhanced by Increasing the reaction interface and reducing the viscosity of stag. As the reduction process proceeds, the !ead-containing phase in the slag vansshed off, the zinc mejijite and iron-zinc spinel phases gradually increased, the sijicate structure of stag ss changed from simple SiO" to Si2O7, and the meiiing temperature and viscosity of the stag Increase accordingly. The dreci smeiiing process for treating !ead-silver eaching residues mixed with !ead concentrates can meet the requrrements of reduction smeiiing production though controlling reduction smeiing stag with FeO/SiO2=1. 6,CaO/SiO2 = 0. 6, and ZnO ) 20 w.. %. [ABSTRACT FROM AUTHOR]

In the melting process, the fundamental slag system of PbO-CaO-SiO2-FeO-ZnO was chosen based on the composition and phase of the jarosite residue and melt agent. The phase diagram of the slag system was drawn by FactSage thermodynamic software, combined with relevant slag performance measurement tests to explore the effect of changing the FeO/SiO2 ratio and CaO/SiO2 ratio on the physical and chemical properties of the slag. The results showed that if there are no more additional components in this system, the melting point gets higher with the FeO/SiO2 ratio increasing, and the melting point became lowest (1 338 °C) when the FeO/SiO2 ratio was 0.92. When the CaO/SiO2 ratio increased from 0.3 to 0.8, the melting point shows a decreasing trend, while the CaO/SiO2 ratio is 0.78, the lowest melting point appeared, and the value is 1 385 °C. The viscosity of slags with a low melting point was measured, and the results showed that when the temperature was 1 500 °C, the viscosities of all slags were less than 0.5 Pa ⋅ s. It means that the smelting requirements for fluidity could be achieved. Finally, the optimized slag adjustment scheme was proposed which is adding CaO and reducing SiO2 to a CaO/SiO2 ratio of 0.78. It is beneficial to the subsequent iron extraction after slag adjustment because the phases of slag are mainly magnetite and silicate. [ABSTRACT FROM AUTHOR]

The high-magnesium gangue severely affects the melting performance and fluidity of slag in nickel matte smelting. To detect the adaptability when the CaO-modified slag for treating high-magnesia nickel sulfide concentrate in flash smelting, the synergistic effect of MgO and other oxides on the microstructure and physicochemical properties of slag were analyzed through molecular dynamics simulation associated with the experimental analysis. The results indicate that the MgO content increases from 5 wt% to 11 wt%, part of the Fe2+ ions in silicate are gradually replaced by Mg2+, and some of them are transformed into Fe3+ in the external atmosphere. Accordingly, the generated Fe3+ may destroy the bridge oxygen between Si4+-O2--Si4+ and more complex silicate ions will be dissociated into SiO 4 4+. As a consequence, the Q0 proportion in the modified high-magnesia smelting slag improved from 24.33% to 29.69%, and the n (BO/T) decreased from 1.45 to 1.29. However, when MgO content is high enough, SiO 4 4+ tetrahedron ions may attract Fe2+ and Mg2+ to form (Fe, Mg) 2 SiO 4 with a more robust interaction network structure, resulting in an adverse effect on melting temperature and ions diffusion coefficient. The modified nickel slags with 5–11 wt% MgO represent hospitable melting temperature less than 1320 °C, viscosity lower than 0.091 Pa s, and surface tension between 0.4811 N/m to 0.4838 N/m. In brief, the CaO-modified slag turned out to be conducive for treating high-magnesium nickel sulfide concentrates in flash matte smelting, especially for those containing MgO less than 7 wt%. [ABSTRACT FROM AUTHOR]

Due to the poor separability and low reducibility of fayalite in iron extracting from smelting waste slag, the composition of the original slag was modified for the nickel matte smelting process. Based on molecular dynamics simulation, thermodynamic calculation and experimental analyses, the influence mechanism of Fe/SiO2 ratio on physicochemical properties, Fe-containing phases and microstructure of the CaO-modified nickel matte smelting slag was investigated, to improve the FeO activity in the final slag and facilitate the subsequent iron extraction process. The results show that the SiO44− is the main form of silicon-oxygen anions in the FexO-SiO2-CaO-MgO-"NiO" slags. As the Fe/SiO2 ratio increased from 1.0 to 1.6, the fraction of SiO44− (Q0) in 15 wt pct CaO-modified nickel matte smelting slag are remarkably improved, and the degree of polymerization of silicate network is reduced correspondingly. Besides, the CaO-modified nickel slags with the Fe/SiO2 ratios of 1.2 to 1.4 present appropriate melting temperature, viscosity characteristics and interfacial tension between slag and matte. It indicates that the modified nickel slags are suitable candidates for nickel flash matte smelting. The concentration of Mg1−xFexO in 15 wt pct CaO-modified nickel slag is improved with increase of Fe/SiO2 ratio, which is conducive to the iron extraction from the smelting residues subsequently. [ABSTRACT FROM AUTHOR]

The melting point and volatilization characteristics of a fluorine-containing slag were investigated under different heating rates and premelting processes. The "hemisphere method" was used to detect the melting point, and the results showed that the measurements for the fluorine-free slag increased with increasing heating rate, and the deviation reached 60 °C and was affected by the hysteresis and fractional melting. The measured values and volatilization of the fluorine-containing slag decreased with increasing heating rate. The weight loss reached 16.8%, and the melting point deviation reached 90 °C, which was primarily affected by the volatility. The melting point of the synthetic fluorine-containing slag was 70 °C higher than that of the premelted slag due to flux volatilization of 8.3%. Scanning electron microscopy-energy dispersive spectroscopy revealed a large amount of CaF2 on the surface of the melted slag. The internal crystals in the synthetic slag were mainly diamond-shaped calcium fluoroaluminate (3CaO·3Al2O3·CaF2) and those in the premelted slag were needle-shaped cuspidine (3CaO·2SiO2·CaF2) that formed during secondary crystallization. Two factors that impacted the volatilization were proposed: one is the content of free CaF2, and the other is the slag structure. Based on these factors, volatilization models for synthetic and premelted fluorine-containing slags were established. This work is of significance for relevant measurement specifications to ensure the repeatability and comparability of the physicochemical properties, especially for volatile-containing slags. [ABSTRACT FROM AUTHOR]

Large quantities of residual slag with high Fe content are left behind in pyrometallurgical nickel processing. How to separate and recover iron from the high fayalite residue is still a problem because iron mainly exists as iron-magnesium silicate in slag. This article suggests that the slag for nickel smelting is adjusted by increasing the amount of lime, partly instead of quartz, to form liable reduction compounds for subsequent Fe extraction. Based on the thermodynamic analysis and phase diagram of the FeO-SiO-CaO-MgO slag system, the new slag composition was chosen, the suitable melting point of relevant slags was measured, and the phase change was observed. The new slag with a composition of 7 to 9 pct MgO, 10 to 15 pct CaO and 1.5 to 1.8 Fe/SiO was found to work well for nickel matte smelting. With the increase of CaO and decrease of SiO content in slag, Ca(Fe, Mg)SiO and Mg(Ca)FeO are the main existing phases instead of (Fe, Mg)SiO in the residual smelting slag. More than 50 pct of Fe-containing phases are in the form of MgFeO when 15 pct CaO is added, which is what we want because the MgFeO is much better for magnetic separation and reduction than the original (Fe, Mg)SiO. In this way, Fe can be much more easily extracted from residual slag and have multipurpose benefits. [ABSTRACT FROM AUTHOR]

To improve the conditions of extracting iron from nickel smelting residues, the composition modulating from FexO-SiO2-CaO-MgO-"NiO" slag source for matte smelting using high MgO nickel sulfide concentrate was carried out. Based on the molecular dynamics simulation and experimental characterization, the effect of CaO content in nickel slags on the physicochemical properties, the microstructure evolution, and the feasibility of subsequent iron extraction were analyzed. The results showed that, for nickel smelting slag with 9 wt.% MgO, 13–15 wt.% CaO and Fe/SiO2 ratio of 1.2, the melting temperature of nickel slag was lower than 1200 °C, and the viscosity was lower than 0.22 Pa·s at 1350 °C. The electric conductivity was similar to that of the industrial slag, and the interfacial tension between slag and matte was relatively large, which ensured a good separating characteristic. It not only met the requirements for the slag performances in the existing flash smelting process but also improved conditions for the subsequent iron extraction. Additionally, it could be adapted to the current situation where an increasing MgO content exists in the nickel sulfide concentrate. [ABSTRACT FROM AUTHOR]