According to the geological survey of Pakistan and available data regarding iron ore reserves [2] are as follows in Table 1.

Table 1.Reserves of iron ore in Balochistan, Pakistan.

It is reported that in the financial year of 2018, more than 5,000 operational mines and around 50,000 small and medium enterprises were present in Pakistan with more than 140,000 employees (0.23% of the total country’s employed population) [6]. Magnetite sand/ore is the most magnetic naturally occurring mineral that occurs in different parts of the world.

Figure 1.Geological (up) and satellite (down) map of Padag area district, Chaghai, Balochistan.

In Balochistan, an area of Padag is a mountainous and desert plain zone, located in the district Chagai, approximately coordinates 29.00305˚N, 65.31538˚E. Geological map (up) and satellite image (down) of magnetite sand/ore are shown in Figure 1.

Pakistan holds around 1.4 billion tons of iron ore [2], whereas year-wise production of iron ore from 2017 to 2021 is shown in Figure 2. The reported differences in mining of iron ore between 2017 to 2021 and 2020 to 2021 are 60.60% and 40.44%, respectively [7].

Figure 2.Mining of iron ore in Pakistan from 2017 to 2021.

In 2019 top ten steel-producing countries were mentioned by the World Steel Association [8]. Pakistan contributed only 0.18% in world steel production, ranked 39th out of 50 countries as shown in Figure 3.

Figure 3.Worldwide crude steel production percentage (2019).

Different beneficiation techniques are used worldwide [9][10] for low-grade iron ore, one of them is magnetic Separation.This separation is based on differences in the magnetic susceptibilities of minerals. Magnetic minerals (e.g., magnetite, pyrrhotite, ilmenite) are attracted to the magnetic field as concentrate, while non-magnetic minerals (e.g., quartz, feldspar, calcite) are left as tailing. Two types of magnetic separators are used: one is a high-intensity magnetic separator (HIMS) with a magnetic field up to 20,000 gauss, and the other is a low-intensity magnetic separator (LIMS) with a magnetic field of 1000 - 3000 gauss [11]. Second separation technique is the shaking table depends on gravity differences and differential movement of particles along an inclined, shaking surface. Particles of higher density move in a different path than lighter ones [12]. A slurry of ground ore is fed onto a table with riffles. The table shakes in a longitudinal motion while water flows transversely. Shaking table technique produces a high-grade concentrate, environmentally friendly (no chemicals) involved in it. Froth flotation is another physicochemical separation technique [13] used mainly for the beneficiation of ores, especially sulfide and oxide minerals. The process depends on the fact that certain minerals attach preferentially to air bubbles due to their hydrophobic surfaces [14], while others remain in the aqueous phase. When air is passed through a mixture of finely ground ore and water containing suitable reagents, the hydrophobic particles rise to the surface with bubbles, forming a froth, which is collected as a concentrate. Schematic detail of magnetic separation, shaking table and froth flotation technique is shown in Figure 4.

Figure 4.Schematic diagram for beneficiation techniques.

Magnetite sand/ore to obtain the concentrate and tailing from the head sample. This LIMS is an easy, non-destructive and eco-friendly technique for iron containing minerals/ores.

Although significant work has been reported on beneficiation of low grade iron ores using magnetic, gravity, and floatation techniques, limited information is available regarding the beneficiation behavior of magnetic sand deposits from Balochistan, Pakistan. Furthermore, these indigeneous magnetic bearing sands dependent on the particle size enrichment have not been investigated systematically. Therefore, present study aims to evaluate the effect of particle size on the beneficiation efficiency of Balochistan magnetic sand using low intensity magnetic separator (LIMS) technique was used for the beneficiation of dry test and wet test. Iron recoveries (R) were calculated by following equation [15].

Here F and C represent feed and concentrate, whereas f and c represent Fe grades of feed and concentrate, respectively.

The Magnetite sand/ore sample was arranged from an area of Padag, District Chagai, Balochistan, with approximate coordinates 29.00305˚N, 65.31538˚E and brought to Mineral Technology Center (MTC) PCSIR Lab, Quetta for R&D in house project. To prepare 20 Kg composite of magnetite ore, samples were collected at a depth of 0 - 1 meter. Twenty individual increments of approximately 1kg each were collected from different points and combined to obtain a 20 Kg composite sample. The composite /head sample was in the form of granular sand. Mixing, coining and quartering, followed by a cup mill were done for X-Ray Diffractometer (XRD) and chemical analysis.

Conventional gravimetric, volumetric and instrumental methods were used for the determination of chemicals. Silica (SiO₂) and associated minerals contents in head samples, concentrate, and tailing. Determination of iron content was done by using potassium dichromate as a standard solution in redox titration (ASTM E-246-01), EDTA titration method was used for aluminium (Al) analysis (ASTM E738-05), Jenway Limited (England-PFP7) flame photometer was used for potassium and sodium analysis [14].

500 g of head sample (in granule form) was used for sieve analysis by using Octagon 200, Eondecotts England sieve shaker. Six different mesh numbers were obtained and used for the experiment. Step-wise depiction of the procedure followed for the beneficiation process of magnetite sand/ore by using low intensity magnetic separator (LIMS) is shown in Figure 5(a)-(g).

Figure 5.Depiction of methodology from (a) to (g).

Flow sheet diagram for the Beneficiation of magnetite sand/Ore of district Chaghai, Balochistan, is shown in Figure 6.

Figure 6. Flow sheet diagram of beneficiation process.

Optimum conditions applied for dry and wet tests are shown in Table 2.

Table 2.Optimum conditions for separation tests (dry & wet).

Mineralogy of the head raw sample was carried out by using XRD (Equinox 2000 Thermo Fisher Scientific, USA instrument (CU Kα1)). Figure 7 shows the XRD patterns of the sample. The presence of peaks at (311), (533) and (731) planes corresponds to the magnetite in the samples with higher concentration; however, intensity peaks at (101), (102) and (112) correspond to quartz/silica, as reported in the literature.

Figure 7.XRD pattern of the head sample.

Similarly, characteristic peaks of magnetite with hkl plane indices (as shown in Table 3) are well matched with JCPDS card numbers 46-1045, 05-0586, 19-0629, 33-0664 and 36-0426 [16][17].

Table 3.XRD details of head sample.

Constituents present in the head sample are shown in Table 4.

Table 4.Chemical analysis of head sample.

Table 5 shows the results of sieve analysis and Figure 8 shows the graph between the mesh no and weight in percent of head sample. Figure 9 shows the percentage retained and passed in different fractions/mesh sizes. Figure 10 shows the distribution of iron (Fe) percentage and silica (SiO₂) percentage contents in different mesh sizes. It is observed that both Fe and SiO₂ contents are showing an inverse relation as mesh size was reduced. Fe showed its maximum content percentage (49.70) in −150 + 200 mesh whereas at the same mesh size SiO₂ showed minimum content percentage (26.02) in head sample.

Table 5.Sieve analysis.

Figure 8. Weight in percentage of head sample.

Figure 9.Cumulative weight (%) of head sample retained and passed through different mesh no.

On the basis of XRD, chemical analysis and particle size, it is observed that the head sample is mainly consisted of Magnetite (Fe₃O₄). For the removal of gangue, magnetic separator technique was used on different mesh sizes. In present research low-intensity magnetic separator was applied for ferromagnetic minerals like magnetite and paramagnetic minerals like hematite [18]. Head sample analysis depicted in Table 3 reveals that it is mainly composed of two major constituents: iron (Fe) 32.69% and silica (SiO₂) 47.26%.

Dry and wet tests were performed, as reported in literature [18], to separate out Fe from SiO₂ via five different mesh numbers through Lab scale single drum magnetic separator (WS 201 blue Ribbon). Results obtained by using mesh size +50 exhibited the lowest Fe contents (11.50%) with highest SiO₂ contents (69.20%) among the investigated size fraction, therefore, this fraction was excluded from subsequent separation test. For each test, 1000 g of sample was used to obtain concentrate and tailing. Magnetic drum rotational speed was kept constant for both dry and wet separation tests as shown in Table 2. Figure 10 showed the distribution of Fe and SiO₂ percentages in six different mesh size trials conducted on magnetic separator.

Figure 10. Iron (Fe) and Silica (SiO₂) percentages in different mesh sizes.

3.4.1. Dry Test

Head sample having 32.69% Fe content and 47.26% of SiO₂was screened into five different particle size/friction using a series of mesh sizes. Table 6 represents the concentrate and tailing results obtained at different mesh sizes for the yield of Fe and SiO₂ concentration and tailing fractions by using a dry single drum magnetic separator. It is clearly observed, Fe was around 47% with a higher fraction of SiO₂ (30%) at coarser size (−50 + 80), as the size decreased and fining, the Fe (%) recovery increased and reached a maximum value (70%) with mesh size −150 + 200 with the least SiO₂ impurities. However, this trend deviates at the fine mesh size (−200), indicating that at the fine size, magnetic efficacy is decreased, as shown in Figure 11(up).

Table 6. Dry magnetic separation.

Similarly, tailing percentage represents the efficient effect of magnetic separator and showed that as the mesh size was getting finer, the SiO₂ tailing percentage was increasing and maximum Fe was separating from the gangue mineral. However, at the fine mesh size, the liberation of magnetic Fe from the non-magnetic SiO₂was decreased as shown in Figure 11(down), which depicts that mesh size plays a very important role in the efficiency of dry magnetic separator and it shows the best results only for the optimal range that is around −150 + 200 mesh number. Enhanced liberation of magnetic selectivity and Fe enrichment is attributed to the improved magnetic separation performance at finer particle sizes. However, particle aggregation and entrainment effects reduce the efficiency at excessive size reduction.

Figure 11. Concentrate percentages of iron (Fe), silica (SiO₂) and weight recovery (up) and tailing (down) based on different mesh sizes by dry magnetic separator technique.

3.4.2. Wet Test

Head sample having 32.69% Fe content and 47.26% of SiO₂was screened into five different particle size/friction using a series of mesh sizes. Table 7 represents the results obtained at different mesh sizes for Fe % and SiO₂ % in concentrate and tailing fractions by using a wet single drum magnetic separator. It is seen that the concentration for Fe was around 42% with a higher fraction of SiO₂ (31%) at coarser size (−50 + 80) and the same trend continued as the size was decreasing and fining and reached a maximum value of 64.4 % with mesh size −200 and the least SiO₂ contents, as shown in Figure 12(up). Similarly, results obtained from tailing percentage with maximum rejection of non-magnetic SiO₂ from the gangue mineral by using wet magnetic separator are shown in Figure 12(down).

Table 7.Wet magnetic separation.

Figure 12. Wet Iron (Fe), silica (SiO₂) and weight recovery (up) and tailing (down) based on different mesh sizes.

On comparison with dry magnetic separator, it is observed that at the fine mesh size (−200), the efficiency of wet magnetic separator is decreased, as was the case in dry magnetic separator and overall, it is suggested that both dry and wet magnetic separators yield good results as the mesh size was decreased and declined at ultrafine particle size [15]. However, the Fe recovery percentage for wet magnetic separator showed an inverse trend with mesh size and continues to increase and reaching a maximum recovery (93.65%) at the fine (−200) mesh size as shown in Figure 12(down). This shows that the separation efficiency is governed not only by particle size and magnetic susceptibility but also by slurry hydrodynamics. Presence of water enhances the reduction in mechanical entrainment and particle dispersion, resulting in improved rejection of non-magnetic gangue minerals.

The results obtained in present study are consistent with the literature reporting that the efficiency of magnetic separation of low grade iron ores are significantly influenced by the particle size. Sis et al. [18] reported that magnetic separation performance and concentrate grade were enhanced at finer particle sizes. Similarly, another group of researchers also reported that appropriate size reduction plays a vital role in the Fe recovery [10].