Study of the spectro‐chemical signatures of cobalt–manganese layered oxides (asbolane–lithiophorite and their intermediates) by Raman spectroscopy

Abstract

In this study, Raman microspectroscopy is applied to investigate two manganese oxide phases: lithiophorite [(Al,Li)Mn 4+ O 2 (OH) 2 ] and asbolane [(Ni,Co) x Mn 4+ (O,OH) 4 ·nH 2 O], along with their intermediates ('asbolane-lithiophorite intermediates': ALI). These oxides typically incorporate variable concentrations of Co, Ni, Cu and Li. They represent a group of economically interesting phases that are difficult to identify and characterize with classical X-ray diffraction techniques. We show that Raman micro spectroscopy is useful to the investigation of those phases, but they require to be tested in very low laser power conditions to avoid sample degradation (e.g. 0.2 mW with λ = 532 nm). We propose reference Raman spectroscopic signatures for lithiophorite, asbolane and ALI phases. These spectra are mainly composed of two spectral domains, the first one is located between 370 and 630 cm À1 and the second one between 900 and 1300 cm À1 . We then assess the impact of their highly variable chemistry on their Raman peak positions, intensities and FWHM using a semi-systematic curve-fitting method profiled for these phases.

Automated curve fitting and unsupervised clustering of manganese oxide Raman responses

“…Figure shows the spectral decomposition of representative spectra of asbolane and lithiophorite. These modelled peaks are in good agreement with previous results on those phases by Burlet and Vanbrabant . The spectral decomposition of the five remaining phases in Figure is based on representative examples of each phase.…”

“…The conducted results also reinforce the strong affinity already stated by Burlet and Vanbrabant between asbolane and lithiophorite. The main distinctive spectral features of this group is the intermediate intensity vibration observed below 500 cm −1 and the very reduce Raman activity above 625 cm −1 .…”

“…By contrast, a solution with seven‐seed curves leads to a separation of both vibrations. The seven‐seed curve solution could be regarded as a better approach, but both models are unable to separate the asbolane overlapping peaks located at 497 and 456 cm −1 as described in Burlet and Vanbrabant . The risk to integrate non‐Raman‐related signal variations, such as noise or fluorescence components actually increases with the number of seed curves.…”

“…The main characteristics of the selected samples are summarized in Table that includes their origin, their geochemical content acquired by semiquantitative scanning electron microscope energy dispersive spectroscopy and their eventual phase identification by X‐ray powder diffraction (XRPD). The scanning electron microscope energy dispersive spectroscopy and XRPD analyses conditions were already presented by Burlet and Vanbrabant . The Raman instrumental and acquisition parameters are summarized in Table .…”

Identification of waste cooking oil and vegetable oil via Raman spectroscopy

“…It has been widely used in petrochemical engineering, [14] biomedicine, [15,16] geoarchaeology, [17] gem identification [18] and so on. Raman spectroscopy is extremely insensitive to polar materials like water and enjoys a bright application prospect in food quality control.…”