Abstract
Saprolitic nickel laterite is characterized by relatively low iron and nickel contents. Iron and nickel oxides are reduced to form fine ferronickel particles that disperse and embed in silicates in the reduction process, limiting the application of magnetic separation to extract ferronickel. Additives are applied to promote the aggregation and growth of ferronickel particles, then the large ferronickel particles will be separated by fine grinding and recovered via magnetic separation. Calcium sulphate is considered to be capable of increasing the size of ferronickel particles considerably. Due to the decomposition of calcium sulphate in the reduction process, the mechanism of calcium sulphate on the aggregation and growth of ferronickel particles should be conducted studied in-depth. The current work explores the effects of calcium sulphate, elemental sulphur, and calcium oxide on the formation of ferronickel particles in a saprolitic nickel laterite ore. The results showed that the formation of an Fe-FeS eutectic and the mineral structure transformation contributed by calcium oxide were all conducive to the mass transfer of ferronickel particles in gangue, ferronickel particles aggregated and grew up at the boundary between the hole and the gangue. The self-reduction, fine grinding, and magnetic separation of nickel laterite ore in the presence of three types of additive were examined. Nickel laterite ore with 7.88 wt% coal, 12 wt% calcium sulphate reduced at 1200 °C for 30 min, a ferronickel concentrate of Ni 8.08 wt%, and Fe 79.98 wt% was obtained at a nickel and iron recovery of 92.6% and 79.9%, respectively.
Highlights
The annual global demand for nickel has increased tremendously due to its numerous applications, especially advantageous for the production of stainless steel, alloys, batteries, and catalysts [1,2,3,4,5,6]
The thermodynamic analysis of the carbothermic reduction roasting of nickeliferous limonitic laterite ore has been performed by Pickles [41]
16 wt% reduced at 1200 ◦ C for 30 min, a ferronickel concentrate with 8.52 wt% Ni, and 80.75 wt% Fe was obtained by magnetic separation
Summary
The annual global demand for nickel has increased tremendously due to its numerous applications, especially advantageous for the production of stainless steel, alloys, batteries, and catalysts [1,2,3,4,5,6]. Nickel laterite deposits are classified into two distinct types: limonitic deposits found in the surface layer while the bottom layer is referred to as saprolitic deposits [14]. Nickel and iron are difficult to concentrate by physical beneficiation due to the low nickel and iron content [15] and isomorphic goethite or serpentine crystalline structure [9]. Metals 2020, 10, 423 this type of ore at moderate temperatures to form a ferronickel alloy, which will be separated from the gangue by magnetic separation, is a useful method to obtain a ferronickel concentrate [3,16,17,18].
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