Introduction

Extraction of nickel from the widely occurring late­rite ores has become an important task of research [1 – 9]. Previous studies have shown that direct reduction roasting process followed by magnetic separation is an effective method for recovering nickel from laterite nickel ores [10 – 17]. To obtain nickel alloy powder with high nickel content, iron reduction needs to be controlled in the direct reduction roasting process. Selective reduction can be achieved by adjusting the reducing atmosphere [18 – 19] and the number of additives [20 – 22]. Li et al. [10] found that FeS is produced by direct reduction with the Na2SO4 additive. The formation of the Fe/FeS eutectic promotes the growth of Ni/Fe particles; simultaneously, in the magnetic separation process the nonmagnetic FeS will go to the tailings thus achieving the purpose of selective reduction. Also, the formation of FeS promotes the growth of metal particles. Jiang et al. [25] found that Na2SO4 reacts with silicates producing low melting point nepheline and suppressing FeO reduction by inhibiting the diffusion of the reducing gas; it can also promote the growth of nickel-iron particles through the formation of FeS. In the FeO reduction process, the diffusion of the reducing gas was impeded due to the increase in the amount of liquid phase in the roasting system. All of the above studies found that FeS plays an important role in the selective reduction of laterite nickel ore. In direct selective reduction of laterite nickel ore, FeS also serves as a paramagnetic film covering the FeO surfaces. That thin layer blocks the contact between the reducing gas and FeO suppressing the reduction process. Iron-rich, it can be used as a nanoparticle’s precursor in food technology, biomedicine, energy and fuel production, etc. [26, 27]. The best possible application of the iron nanoparticles precursor is for metal fuel which is illustrated in Fig. 1 [27]. Iron-rich by-product shall be seen as a primary source for the extraction processes to be used in the future.

Material and Methods

Data on tailings/by-products is taken from selective reduction process at the Research Unit for Mineral Technology, National Research and Innovation Agency of Indonesia, South Lampung, Lampung, Indonesia. First, the by-product was brought through a 200-mesh shaker sieve. After that the sample was dissolved in aqua regia for 5 days, diluted 50 and 1000 times, and analysed first by the ICP-OES Analytika Jena PQ9000 (with the resulting data converted in excel from ppm to weigh percent); and then by the XRD PANalytical X’Pert3 Powder (in the 200 mesh sample size, the 2θ is in the range of 10 – 80°, step size 0.05, and analysis data by High Score Plus) (Fig. 3). For SEM–EDS Thermo-scientific Quatro 6 with magnification 5000× was used and Bruker for EDS.

Results

ICP and UV–VIS Study

Table 1 gives tailing specific chemical composition: 0.74 wt% Ni, 39.45 wt% Fe, 5.1 wt% Mg. Fig. 2 gives Fe, Ni, Mg, Mn, Al, and Co ratios in the tailings according to their absorbance and wave lengths [28]; therefore, the same elements are detected by UV–VIS and ICP. The agreement of the ICP and UV–VIS result shows that the aggregate amounts of components in both tests are the same; for example, iron is the greatest ingredient while cobalt, nickel, and manganese are the least ones.

XRD Study

In the sulfide phase, iron occurs in a higher percentage than in magnesioferrite, forsterite, and quartz phases, where there is less iron which occurs together with constituent elements magnesium or aluminium. The Rietveld refinement calculation results agree with the XRD results in Table 2. Significantly, it is the first time that the tailing product is addressed as raw material.

SEM–EDS Study

This study gives the same results for the elements and phases of the tailings which can be further identified in microstructure. The morphology of tailings, as shown in Fig. 4, convincingly proves that the major elements in the tailing are iron-sulfur, iron-magnesium-silica-oxide, natrium, and quartz extracted in selective reduction with sulfur appearing in XRD. From Table 3, the magnesium-iron-aluminium is appearing in spots 2 and 4 indicating the magnesioferrite and forsterite phases.

Conclusions

Based on the results, the tailing includes such phases as iron-sulfur, iron-magnesium-aluminium, and silica which can be interpreted so that the tailing is iron-rich and not usable after process. The process under consideration can serve as reference for further processes such as acid and base leaching. Pure iron extracted from tailings can be used for metal fuel in the future.