Hydroxyl-stretching region in the Raman broad scans on minerals of the vivianite group

Abstract

Vivianite is a hydrated iron phosphate mineral (Fe3(PO4)2·8H2O), crystallized in a monoclinic system. It is the endmember of a mineral series known as the vivianite group, where minerals have the general formula A3(XO4)2·8H2O, A is a divalent metal cation and X is phosphorus P or arsenic As. Today, vivianite is attracting interest as a promising material for recovering phosphorous from wastewaters. In fact, the presence in wastewater sludges of soluble iron and phosphorus can lead to vivianite formation. As a crystal, it is a naturally occurring Van der Walls material. It can be easily characterized by means of Raman and infrared spectroscopies. Here we will consider the Raman spectroscopy, precisely that related to the hydroxyl-stretching region. We will propose the deconvolutions in q-Gaussian functions of spectra from RRUFF database, comparing the obtained results with those available from literature. Besides vivianite, we will consider also baricite and bobierrite for comparison (baricite and bobierrite are two other members of the vivianite group). About the hydroxyl-stretching region and the use of q-Gaussians, we take the chance to continue a discussion regarding the Raman spectroscopy of water, discussion that we started in March 2024.