Quantification of the REE3+ aqua ions and chloride species in aqueous fluids by in situ Raman spectroscopy using perturbations of the water band

Description

Here we develop a new method using the water vibrational mode which is modified by the addition of REE3+ ions and REE chloride species. The Raman spectra for the vibrational band of water (2700 to 3900 cm-1) were collected at 25 ºC in aqueous solutions buffered at pH 2 with variable NaCl (0.2 to 3.2 m), NdCl3 and YbCl3 (0.1 to 0.6 m) concentrations. The water vibrational band can be fitted by three Gaussian sub-peaks, which were further quantified using a multivariate curve resolution analysis. The water band was de-convoluted into individual spectra representing bulk H2O and the perturbations of the water band caused by the addition of Cl-, REE3+, and REE chloride species (REECln3-n). The multivariate analysis indicates that water molecules in the REE3+ ions hydration shell perturbed by Cl- ions result in an asymmetric Raman peak at 3430 cm-1 with a shoulder at 3320 cm-1. Quantification of REE speciation based upon these perturbations of the water band indicates that the REE3+ aqua ion dominates in acidic solutions at 25 ºC, and the REE chloride species (REECl2+, REECl2+, and REEClin3-n·Clom- ) can make up to 20 mol% in Cl-rich solutions (>3m Cltotal).

Institutions

Categories

Funding

Licence