Purwadi, et al., in 2019, reported that Rare Earth Elements (REEs) are indispensable in the manufacturing of renewable energy and clean technologies. Due to the high demand for REEs, mine waste, called “tailings”, are possible resource for REEs. In this study, tailing samples were collected from two tin mine tailings in Bangka Island, Indonesia, and analyzed using inductively coupled plasma optical emission spectrometry, x-ray powder diffraction, and Fourier transform infrared - attenuated total reflectance.
Results showed that the tailing samples were identified as quartz and contained a high amount of erbium between 111.6 and 3,768.4 μg/g. Absorption features in infrared reflectance spectra were related to REE concentrations. The authors concluded that a positive correlation between erbium and two absorption features that have not been reported before: One feature is centered at 500 nm with a correlation of 0.685, and one is centered at 674 nm with a correlation of 0.829.
Tailings were analyzed using ICP-OES, XRD, and FTIR-ATR. By using ICP-OES, we identified a high anomaly of Er concentration reaching up to 3,768.4 μg/g in tailing samples. Based on the results of the XRD and FTIR-ATR analyses, tailing samples were identified as mostly quartz. Therefore, the authors concluded that the tailing samples were REE-enriched quartz, but the reason behind this enrichment remains unknown. It was expected to find xenotime in tailing samples, but due to mineral extraction during mining operation, it was probably extracted together with tin ore. Two absorption features at around 500 nm and 674 nm were observed in the reflectance spectra of the tailing samples. Three spectral parameters (band ratio, absorption band depth, and absorption band) were derived from both absorption features and had strong correlations with Er with correlation coefficients varied between 0.604 and 0.829.
Considering correlation coefficients coupled with the position of Er absorption features (in Er oxide and xenotime spectra) and Er concentration in the tailing samples, the authors concluded that both absorption features are due to the presence of Er. Both absorption features might be due to Fe, but results show that it is most unlikely due to Fe because the concentration of Fe is too low in the tailing samples less than 3,839.2 μg/g.
This study has also shown that the absorption feature related to REEs can shift when REE ions are incorporated into different minerals. Further research is required to investigate the enrichment of REE especially Er in the samples, and the coordination complex of Er in quartz crystal structures. It is also worthy to investigate whether both Er absorption features can be detected using airborne or satellite remote sensing as the success rate of detecting Nd-related absorption feature is low. If successful, then it can be an alternative to detect REEs using remote sensing technique because so far, only one study detected Nd-related absorption features in an airborne remote sensing image. [The remote sensing of these elements also has application to off-world exploration].
Original working URL: https://i2mconsultants.com/downloads/corp/2018_jag_purwadi_ref_reprint.pdf
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