University of Twente Student Theses


Spectral analysis of lithium-bearing micas with shortwave and longwave infrared spectroscopy

Mekonenn, Selamawit Abdissa (2023) Spectral analysis of lithium-bearing micas with shortwave and longwave infrared spectroscopy.

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Abstract:Lithium is one of the critical raw materials used for many applications, including rechargeable batteries for electric vehicles, laptops, and cell phones. Minerals, particularly mica minerals, are the most common and economically valuable lithium-bearing minerals found in hard rock. However, it is essential to recognize that not all mica minerals contain lithium; therefore, identifying and distinguishing mica minerals is crucial. The spectral characteristics obtained from infrared spectroscopy play a vital role in identifying and distinguishing mica minerals. Nevertheless, numerous factors can influence the diagnostic spectral features of mica minerals. Among these, elemental substitutions have a significant impact on changing the diagnostic features of mica minerals. This study aims to analyze the spectral characteristics of natural mica minerals and the effect of elemental substitution on the shift of absorption features using long-wave infrared (LWIR), mid-wave infrared (MWIR), visible to near infrared (VNIR), and short-wave infrared (SWIR) spectroscopy, integrated with electron microprobe analysis (EMPA) and X-ray diffraction (XRD). A total of 27 mica mineral samples were used to analyze their spectral characteristics. A spectral stack and scatter plot using major octahedral cation contents were employed to discern the spectral feature differences and determine the shift of absorption features. The EMPA result showed that Si(IV) and Al(IV) are the major tetrahedral cations, while Al(VI), Fe(VI), and Mg(VI) are the major octahedral cations in the studied mica. Additionally, minor concentrations of Cr(VI), Ti(VI), and Mn(VI) also comprise the studied mica. XRD analysis demonstrates that the studied mica minerals exhibit similar diffraction patterns due to peak shifts caused by height differences. On the other hand, the LWIR-MWIR results showed that the studied mica minerals exhibit distinctive absorption features. Additionally, the absorption features obtained from the LWIR part of the spectrum resolve the absorption peak associated with Li-OH bending vibrations. Moreover, mica minerals such as muscovite display a systematic shift in absorption peaks due to the substitution of Al(VI) and Mg(VI) in the octahedral site. In the VNIR-SWIR regions, the studied mica minerals exhibit prominent absorption features. Spectral differences in terms of shape (symmetry and depth) and wavelength positions, resulting from variations in concentrations of major and minor element octahedral cations, allowed for the identification of the studied mica minerals. The stacked spectral features based on increasing major cations such as Al(VI) and Mg(VI) and scatter diagrams plotting 2200 nm features against Al(VI) and Mg(VI) content also display a systematic shift of wavelength positions. Generally, this study demonstrated the limitations of XRD and SWIR spectroscopy for distinguishing the studied mica minerals. Conversely, the LWIR analytical technique emerges as the most promising technique for differentiating the studied micas as well as distinguishing lithium-bearing micas.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Subject:38 earth sciences
Programme:Geoinformation Science and Earth Observation MSc (75014)
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