Molecular Dynamics Simulation on Microstructure and Physicochemical Properties of FexO-SiO2-CaO-MgO-“NiO” Slag in Nickel Matte Smelting under Modulating CaO Content

Abstract

To improve the conditions of extracting iron from nickel smelting residues, the composition modulating from Fe x O-SiO 2 -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/SiO 2 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.Minerals 2020, 10, 149 2 of 15 research results from the literatures [8,9] also show that the liquids temperature and viscosity of liquid phase can be reduced with an appropriate addition of CaO, a low amount of MgO and the reduction of oxygen potential in the system. Jian PAN et al. [6,10] used reduction-magnetic separation to recover valuable metals in nickel slags. It is shown that an increasing CaO content contributes to the enrichment of valuable metals and improves the recovery rate of Ni, Cu, Fe, and other metals. However, when CaO is added to extract Fe from waste slag, a lot of heat is consumed and a lot of waste slag is generated. Therefore, the direct addition of an appropriate amount of CaO and a reduction in SiO 2 in the smelting process is considered to regulate the nickel slag performance to meet the smelting requirements and obtain final slag, which is beneficial to the subsequent extraction of valuable metals. In this way, the proper regulation of the composition of the existing matte smelting slags from the source of solid waste is proposed to replace the past terminal treatment mode in the present study.In the production practice, MgO content in nickel concentrate is required to be less than 6.5 wt.% in the nickel flash furnace smelting system, while the MgO content is generally as high as 10 wt.% in the nickel concentrate produced by Jinchuan company (Jinchang, China). Most of the MgO in the nickel concentrate is transferred into the slags, so that the MgO content reaches 8 wt.% to 13 wt.% in the slags when using Jinchuan self-mined concentrates. It is inevitable that MgO content at the current level in slag leads to higher melting temperature, lower fluidity, and worse separation characteristics between slag-matte than before. How to solve the above problems caused by high-MgO-containing slag? Increasing smelting temperature...