Figure 5 shows the volume distribution and cumulative passing of the concentrate particles. Particle diameter ranges from 10 to 200 microns with about 68% of the total volume being 80 microns in diameter. The d50 and d80 are indicated as 57 and 113 microns respectively. The d80 found is in close agreement with the 100 microns suggested earlier. Considering the higher liberation of spodumene grains, it may be indicated that, d80 of 113 microns and particle diameter of 80 microns are good comminution parameters for processing spodumene ore, particularly pegmatites ores of Pilbara origin.
The BSE of the SEM was further used to investigate the morphology and texture of particles in the concentrate. It was coupled with EDS to determine the elemental composition at some points and hence the mineral composition.
Figure 6 and
Table 4 are the SEM photomicrograph and spot elemental composition of the concentrate respectively. It is observed (from
Figure 6a,b) that, it is a well liberated coarse and loose material with varying particles of several microns in diameter; confirming earlier observation.
Spodumene grains were identified using the Si/Al ratio since EDS cannot detect the presence of lithium. The atomic ratio of Si to Al in spodumene is 2.0 hence all grains with spot elemental composition mainly of Al, Si, O and Si/Al ratio of approximately 2.0 corresponds to spodumene. All spots indicated “1” are identified as spodumene.
Figure 6c,d confirm that spodumene is a coarse, dense, crystalline solid with a smooth surface, however, scratches were observed on some grains, which may be due to abrasion during comminution. It suggests that spodumene is a hard mineral that resists wear and tear except when in contact with a harder material. This is confirmed by its relatively high 6.5 to 7.0 value on the Mohs scale of mineral hardness. Spodumene is the major mineral found in the concentrate. It is well liberated but with few mineral associations. Spot “2” has a complex composition with Fe, Mg, Ca, Al, Si, O as the major elements but with varying concentrations at different spots. We attribute these grains to the amphibole group of minerals as indicated in XRD spectra due to the higher concentration of Fe, Mg and Ca at some spots. We could not attribute them to the mica group since the mica group identified by MLA in the concentrate are muscovite and biotite which all contain K in their chemistry but K is absent at these spots. Spots identified as amphibole do not have specific color but ranges from light gray to white depending on the concentration of heavy metals that may be present. The micas (muscovite and biotite) are identified by spot 3 where there is an appreciable higher concentration of K. Spots “4” are composed mainly of Si and O with an O/Si ratio of approximately 2 and therefore identified as quartz. Spots “5” and “6” have a complex composition of Ca, K and Na and are linked to the feldspars, specifically, alkali feldspars and anorthite. We specifically identify spot “5” as albite due to the high concentration of Na at these areas and spots “6” as other feldspars. Hematite was not identified by XRD nor MLA but Spot “7” is identified as such based on the composition. It is composed mainly of Fe and O with an O/Fe ratio of approximately 1.5, confirming its identity. Tantalite and apatite which are typical of LCT-spodumene ore of the Pilbara region are also identified at spot “8” and “9”, respectively. The standard deviations calculated for atomic percent obtained on some mineral grains in the concentrate are shown in
Tables S3–S9. Spot “10” is composed of Sn, Ta, N and O. Though the identification of Sn by EDS is a confirmation of elemental composition in
Table 1, we could not link the identity of this spot to any mineral since its composition did not match with any. We treat it as an impurity that is locked up in the spodumene grain. All major minerals in the concentrate were identified using spot elemental identification by EDS, confirming XRD and MLA analytical results. Raw data (elemental spectrum with their corresponding intensities, weight percent, etc.) generated by SEM-EDS instrument for mineral phases identified can be found in
Figures S1–S8 and Tables S10–S17. Other elements such as Cr, Ti, F, Th, Sn, Zn, Cu, Ni, V, and S were also identified which are associated with the fine inclusion of some minerals. Though Ta, Nb, Sn and other valuable metals were observed, their concentrations are too low to be extracted in an economical manner.