Thermodynamic and Experimental Optimization of Fe Extracting-Oriented Slag Composition for Oxygen-Enriched Top-Blown Nickel Smelting

The slag produced during the nickel pyrometallurgical process is rich in iron (Fe). How to recover the Fe and other valuable metal element is a focus for sustainable development. The utilization of quartz in the smelting leads the Fe in the slag to exist as ferrous silicate, a substance detrimental to subsequent iron extraction. In this work, it is proposed that, to adjust the slag composition in oxygen-enriched top-blowing nickel smelting, adding CaO instead of SiO₂ in the traditional process, to form a new slag composition that benefits and facilitates more efficient iron extraction. In this research, a suitable range of slag composition was selected through thermodynamic calculations under oxygen-rich top-blowing smelting conditions. The reasonable slag composition was determined based on analysis and tests of slag melting performance. A predictive model for the melting temperature of the SiO₂-MgO-FeO-CaO quaternary slag system was developed through optimization-derived design of experiments, A comparative assessment of the performance and phase composition between the new slag and traditional slag was conducted, and the results indicated that the hemispherical temperature of the modified slag decreased from 1410°C (traditional process) to 1382°C, and viscosity reduced from 0.173 Pa s to 0.071 Pa s. The properties of the slag can meet the requirements of nickel oxygen-rich top-blowing smelting. The primary mineral phase in traditional slag and new slag transformed from fayalite and calcium ferrite, respectively, at the same time resulting in higher alkalinity. This transformation is very favorable for the subsequent extraction of Fe.