Abstract
Extraction of limonite ore using dissolved SO2–air is an alternative hydrometallurgical method for nickel recovery. This process is carried out at atmospheric pressure and is shown to have good selectivity of nickel over iron, but with a low recovery yield. The literature refers to the application of alkali roasting as pretreatment in laterite ore leaching to increase nickel recovery. Thus, this study aims to apply the combination method of alkali roasting and leaching to extract nickel from limonite ore (1.33% Ni, 46.61% Fe) from the Southeast Sulawesi region. Three alkali compounds were included in the study (NaOH, Na2CO3 and Na2SO4). The batch-leaching process was carried out at pH 1 and 3 and temperatures of 55 and 80 °C for 180 min. The leach liquors were sampled at 15, 60, 90 and 120 min, and concentrations of the extracted metals were measured by Atomic Absorption Spectrometry (AAS). A mineralogy characterization of the raw ore and its residue after leaching was undertaken by using X-Ray Diffraction (XRD), while the thermal decomposition behavior of the ore was characterized by Thermogravimetry Analyzer (TGA)/Differential Scanning Calorimetry (DSC). The addition of Na2CO3, Na2SO4 and NaOH in the ore pretreatment increases nickel recovery from 14.80% without alkali roasting to 23.99%, 28.15% and 39.22%, respectively. The optimum extraction condition for nickel recovery is at pH 1 and a temperature of 80 °C. However, the highest Ni/Fe selectivity of 24,947 is obtained at pH 3 and a temperature of 80 °C, preceded by roasting in the absence of alkali. Compared to other hydrometallurgical processes, the process studied in this work exhibits lower recovery, but provides an alternative to extract nickel from low-grade limonite ore.
Highlights
The depletion of high-grade nickel sulfide and the growing world demand of nickel have spurred an increasing focus on the processing of low-grade nickel laterite ores [1]
Nickel leaching from low-grade limonite ore using SO2 -dissolved air with roasting and alkali roasting pretreatment has been carried out in this study
X-Ray Diffraction (XRD) results from roasting pretreatment indicate the formation of hematite due to the dehydroxylation of goethite, while those from alkali pretreatment indicate the formation of different mineral phases such as sodium iron silicon oxide
Summary
The depletion of high-grade nickel sulfide and the growing world demand of nickel have spurred an increasing focus on the processing of low-grade nickel laterite ores [1]. It is estimated that approximately 70% of global nickel resources exist as laterite ores [2]. Reported that Indonesia has the globally largest nickel reserves of about 21 million tons in the form of laterite deposits (2018 data). These deposits comprise layers such as the limonite layer, which contains a significant amount of goethite (FeOOH), 0.5–1.7% nickel, 40–60% iron and low silica content; and the saprolite layer with containing about 1.5–3% nickel, with lower iron and higher silica contents [4]. Due to the complex mineralogy, heterogeneous nature and low nickel content, the physical beneficiation of Ni from limonitic laterite ore is very challenging [5].
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