Abstract:Nickel slag is a solid waste rich in iron element generated in the acid leaching process of laterite nickel ore. Due to its high sulfur content, it cannot be used as a raw material for ironmaking and can only be stored in large quantities, which causing environmental pollution and waste of land resources, and becoming one of the urgent industrial solid waste problems to be solved. Therefore, it is necessary to treat nickel slag for resource utilization. Using CO as reducing agent to calcine and desulfurize nickel slag in dispersed state. The influence of CO concentration, time, and temperature on desulfurization rate was investigated. The mineral phase composition, total sulfur content changes, and micro and macro morphology changes before and after the reaction were characterized by X-ray diffraction, X-ray fluorescence spectrometer, and scanning electron microscope, and the process characteristics of desulfurization reaction were explored. The results show that the main mineral phase of nickel slag is hematite [Fe2O3], and the sulfur phase exists in the form of iron alum [K2Fe(H2O)6(SO4)2] and alum [(H3O)Al3(SO4)2(OH)6]. In addition, there are chromium oxide, magnesite iron alum mixed phase, and ferrosilicon compounds. During the roasting process, it includes dehydration reaction, decomposition reaction, and reduction reaction. The main phases involved in the reaction in nickel slag are iron alum, alum acid salt, and hematite. Among them, alum minerals undergo dehydration reaction and decomposition reaction and reduction reaction at high temperature for desulfurization. At the same time, hematite in nickel slag is reduced to magnetite by CO. The desulfurization rate is positively correlated with temperature and time, but after the temperature exceeds 900 ℃, the nickel slag melts and forms a liquid phase, particles merge, and the particle size increases, which is not conducive to the desulfurization reaction. When the CO concentration is 5%, the temperature is 850—900 ℃, and the calcination time is 2—8 min, the desulfurization rate reaches over 95%. XRD analysis shows that hematite in nickel slag is reduced to magnetite, and the sulfur phase is transformed into the corresponding metal oxide form, with pyrite gradually appearing; SEM shows that as the roasting time and temperature increase, the volume and agglomeration of material particles become larger, which is not conducive to roasting desulfurization. Under CO atmosphere, the kinetic mechanism function of nickel slag desulfurization reaction is (1—α)—1—1, the activation energy is 106.67 kJ/mol, and the pre exponential factor is A=105.34. This study provides a theoretical and technical reference for the roasting desulfurization of acid leaching residue of laterite nickel ore and the resource utilization of nickel residue.