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Considering that the low recovery efficiency and the massive loss of valuable metals by the traditional pyrometallurgical process smelting low‒nickel matte. Therefore, this paper focuses on studying the optimal process parameters and the mechanism of sulphation roasting followed by water leaching achieving efficient synchronous extraction of nickel (Ni), copper (Cu), and cobalt (Co) from low‒nickel matte with sodium sulfate as the sulfating addictive. Under optimal conditions, the recovery efficiency of Ni, Cu, and Co metals can achieve 95%, 99%, and 94%, respectively, whereas the recovery efficiency of Fe metal is less than 1%. The results revealed that the mechanism of the sulfating roasting pretreatment could form a liquidus eutectic compound sulfates [Na2Me(SO4)2] (Me = Ni, Cu, Co) at the solid–solid interface, which plays a significant role in promoting the leaching efficiency of valuable metals. Not only enhance the reaction kinetics of sulfation, but improve the utilization efficiency of SO2/SO3. Thus, the sulfation roasting‒water leaching process developing an efficient and eco-friendly pathway to simultaneous extraction of Ni, Cu, and Co valuable metals from low grade sulfide ores. [ABSTRACT FROM AUTHOR]

As a more environmentally friendly and energy-efficient route, the sulfation roasting-water leaching technique has been developed for highly effective extraction of non-ferrous metals from nickel sulfide concentrate in the presence of a Na2SO4 additive. The effects of several important roasting parameters—the roasting temperature, the addition of Na2SO4, the holding time, and the heating rate in particular—have been investigated. The results suggest that about 90 pct Ni, 92 pct Co, 95 pct Cu, and < 1 pct Fe can be leached from the calcine roasted under the optimum conditions. Furthermore, the behavior and mechanism of the Na2SO4 additive in the roasting process have been well addressed by detailed characterization of the roasted product and leaching residue using quantitative phase analysis (QPA) and energy dispersive spectroscopy (EDS) mapping. The Na2SO4 additive was observed to play a noticeable role in promoting the sulfation degree of valuable metals by forming liquid phases [Na2Me(SO4)2] at the outermost layer, which can create a suitable dynamic environment for sulfation. Thus, addition of Na2SO4 might be conducive to an alternative metallurgical process involving complex sulfide ores. [ABSTRACT FROM AUTHOR]

Combining great targeting and cleaner technology is a potential strategic development in the metallurgy and materials industry. This paper proposed a nanomaterial-oriented and integrated pyrohydrometallurgy of low-grade nickel–copper (Ni–Cu) matte: temperature-programed roasting, followed by water leaching and the direct preparation of Cu@Ni–Co core–shell nanoparticles from its leachate. First, a three-step temperature-programed roasting process was designed, in which the effects of the roasting temperature scheme and NaCl additive on the water leaching rates of valuable metals were systematically investigated. Under optimized conditions, the water leaching rates of Ni, Cu, and Co were 96.8, 98.9, and 99.8%, respectively, while that of Fe was nearly zero. The leachate was a chlorine-free sulfate aqueous solution. The addition of NaCl in this study was 10% (100 mg/g), which was 5–10 times less than that in previous studies. The substantial decrease in the amount of chloride added during roasting greatly reduced the high temperature corrosion of chlorine and pollutant emission. It was confirmed that a small amount of NaCl induced the chlorination–sulfation coupling reactions of low-grade Ni–Cu matte in the appropriate roasting scheme, thereby promoting the selective sulfation of sulfides and obtaining chlorine-free roasting products. In addition, the nanopowder with the Cu@Ni–Co core–shell structure was synthesized by low-temperature hydrazine hydrate reduction from the leachate. Summarily, a novel NaCl roasting water leaching low-temperature reduction successfully realized the integration of a cleaner and efficient extraction of valuable metals and preparation of high-value nanomaterials from the low-grade Ni–Cu matte. This cleaner, material-oriented, and short process design greatly expands the industrial application of traditional mineral resources and their extractive metallurgy. • A three-step temperature-programed roasting process was designed for low-grade Ni–Cu matte. • A small amount of NaCl induced the chlorination–sulfation coupling reactions of Ni–Cu sulfides. • The water leaching rates of Ni, Cu, and Co were 96.8, 98.9, and 99.8%, respectively. • Nanopowder with a Cu@Ni–Co core–shell structure was synthesized from leachate by low-temperature reduction. [ABSTRACT FROM AUTHOR]

Sulfation roasting, a common activation technique, is a potential method for cleaner production of nickel from complex low-grade ores. In this study, nickel oxide–sulfide mixed ore concentrate was roasted with the addition of ammonium sulfate under a static air atmosphere, and the roasted products were leached by water, in order to evaluate the extraction of metals. The ammonium sulfate activation roasting was investigated thoroughly and systematically by thermogravimetry–differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy. Particularly, the interface sulfation behavior and path were studied by the density functional theory (DFT) method. The results showed that a large amount of nonferrous metal sulfate (70% Ni, 89% Co, and 90% Cu) was generated, while iron was almost entirely transformed into iron oxide under appropriate roasting conditions of adding ammonium sulfate at a mass ratio of 200%, heating to 650 °C at 10 °C/min, and holding for 120 min. It was found that activation of ammonium sulfate can take two different paths: one in which ammonium sulfate directly reacts with raw ores below 500 °C and the other in which the SO2 decomposed from sulfates (ammonium sulfate, intermediate ammonium ferric sulfate, and ferric sulfate) reacts with the intermediate metal sulfides (NiS and Cu2S). The interface sulfation mechanism of NiS and Cu2S was investigated deeply by DFT method, which showed that there are two paths of sulfation for NiS or Cu2S, and both of them are thermodynamically favored. Thus, a thorough and systematic investigation of ammonium sulfate activation roasting of nickel oxide–sulfide mixed ore is provided; this might be a potential basis for future industrial applications of ammonium sulfate activation roasting techniques in complex mineral metallurgy. [ABSTRACT FROM AUTHOR]