Nickel is one of the most important strategic and industrial resources around the world because of its wide application, but the low-grade nickel ores, such as nickel sulfide, are difficult to process with conventional flotation and smelting or bioleaching technologies. To overcome the weaknesses, researchers with Institute of Process Engineering, Chinese Academy of Sciences developed a new method called ammonium sulfate roasting which used to recover valuable metals from a low-grade nickel ore.

The raw low-grade nickel ore used in this study was obtained from Jinchuan Group Co. Ltd. The mineralogical composition of the nickel ore before and after roasting was carried out by XRD analysis at a scanning speed of 2°/min with Cu Kα radiation. The chemical composition of the leaching residue was analyzed using an atomic absorption spectrophotometer. The roasting-leaching experiments were carried out at a laboratory scale. Fig. 1 shows the flow sheet for the experimental procedure.

In experiments XRD analysis was conducted to understand the mechanism of roasting reaction. The results showed the amount of ammonium sulfate, roasting temperature, and roasting time are important factors that influence the dissolution of metal elements in a low-grade nickel ore. The optimum parameters were as follows: ammonium sulfate/ore ratio, 0.8 g/g; roasting temperature, 400°C; and roasting time, 2 h. Under optimum leaching conditions, the maximum extractions of Ni, Cu, Fe, and Mg achieved are 83.48%,76.24%, 56.43%, and 62.15%, respectively.

The dissolution kinetics of Ni and Mg from the nickel ore was also studied. The results showed that the dissolution kinetics followed a shrinking core model with diffusion through a product layer as the rate-controlling step. The values of apparent activation energy were 18.782 and 10.038 kJ·mol？1 for Ni and Mg, respectively, which were consistent with the values of activation energy reported for diffusion control.

This work was financially supported by the National Natural Science Foundation of China (Nos.20876160 and 21176026). The paper was published in International Journal of Mineral Processing

Fig. 1. Flow sheet of the roasting-leaching process (image by IPE)