Automated curve fitting and unsupervised clustering of manganese oxide Raman responses

Abstract

Natural manganese oxides characterization represents a challenge due to the broad variety of their structures and geochemical compositions along with a frequent poor crystallinity. This characterization requires the ability to conduct both a phase separation and a phase association operation. In this paper, the Raman spectra acquired on a selection of natural manganese oxide minerals are first processed with an automated curve‐fitting model called MnOx. The adjustment of convolution envelope is realized, thanks to the Levenberg–Marquardt algorithm applied on a set of randomly generated seed pseudo‐Voigt curves. The application conditions of the automated curve‐fitting and, in particular, the number of seed curves are investigated with regards to the risk of overfitting. The MnOx model outputs are in a second step treated by data mining techniques and in particular by unsupervised clustering methods. This data processing shows promising results in terms of phase separation when the number of clusters is equivalent to the number of phases. By contrast, the decrease of number of clusters leads to a phase association which reflects spectral affinities between phases. This result shows the existence of 6 to 7 vibrational bands in Mn oxides Raman spectra, with contrasting behaviours between clustering. Thereby, vibrational bands located in the low wave number domain (<510 cm−1) are more mobile and therefore more sensitive to structural modifications, while bands with higher wave number are less affected by structural changes. Besides these results, Raman responses collected during this study provide new refinement regarding the spectral content of some Mn oxides in particular todorokite, nsutite, and chalcophanite. Copyright © 2017 John Wiley & Sons, Ltd.

Raman spectra of natural manganese oxides

“…A selected, representative spectrum of manganite, is reported in Figure a. Measured positions and relative intensity of observed bands are in agreement with data reported by previous works for natural samples, and with the data collected on a synthetic sample by another work …”

“…In the literature, there are many discrepancies regarding the Raman spectra of MnOx, both for the spectra collected on natural phases and for the spectra collected on synthetic phases . The disagreements between the data can be due to many factors such as the experimental condition, the incorrect identification of the examined cryptocrystalline materials, and the wide variety of possible mixtures between different MnOx .…”

Hydrogenetic, Diagenetic and Hydrothermal Processes Forming Ferromanganese Crusts in the Canary Island Seamounts and Their Influence in the Metal Recovery Rate with Hydrometallurgical Methods

“…The obtained intensity are variable due to the multiple acquisition procedure. Mn-oxides usually show three main band frequencies shift regions that can be recognized at 200-450, 450-600 and 600-750 cm −1 [52,54,56,58,70,71].…”

Recent advances in linear and nonlinear Raman spectroscopy. Part XII

“…The Raman spectra acquired on a selection of natural Mn oxide minerals are first processed with an automated curve‐fitting model called MnOx. The adjustment of convolution envelope is achieved using the Levenberg–Marquardt algorithm applied on a set of randomly generated seed pseudo‐Voigt curves . Sanz‐Arranz et al describe the use of amorphous zinc borate as a simple standard for baseline correction in Raman spectra.…”

“…The adjustment of convolution envelope is achieved using the Levenberg-Marquardt algorithm applied on a set of randomly generated seed pseudo-Voigt curves. [240] Sanz-Arranz et al describe the use of amorphous zinc borate as a simple standard for baseline correction in Raman spectra. As an alternative to existing methods of baseline correction, the authors propose a solution based on the use of amorphous zinc borate, an easy-to-find substance, which after a simple processing allows us to correct the baseline of Raman spectra qualitatively, offering a useful and economic reference when an absorbance intensity correction is not needed.…”