Abstract
Characteristic spectral parameters such as the wavelength and depth of absorption bands are widely used to quantitatively estimate the composition of samples from hyperspectral reflectance data in soil science, mineralogy as well as vegetation study. However, little research has been conducted on the spectral characteristic of rare earth elements (REE) and their relationship with chemical composition of aqueous solutions. Reflectance spectra of ore leachate solutions and contaminated stream water from a few REE mines in the Jiangxi Province, China, are studied for the first time in this work. The results demonstrate that the six diagnostic absorption features of the rare earths are recognized in visible and near-infrared wavelengths at 574, 790, 736, 520, 861, and 443 nm. The intensity of each of these six absorption bands is linearly correlated with the abundance of total REE, with the r 2 value >0.95 and the detection limit at ≥75,000 μg/L . It is suggested that reflectance spectroscopy provides an ideal routine analytical tool for characterizing leachate samples. The outcome of this study also has implications for monitoring the environmental effect of REE mining, in particular in stream water systems by hyperspectral remote sensing.
Highlights
Rare earths are valuable resources that play an important role in modern industrial materials
In the spectra of rare earth oxide, absorption bands at wavelengths of 1400 and 1900 nm are related to hydrous minerals, and the several sharp absorption features on visible and NIR wavelengths are due to rare earth elements (REE)
Thereafter, a linear correlation between the depth of each of the six diagnostic absorption features and the concentration of total REE has been found that can be used to estimate the concentration of total REE in ore leachate and river water samples
Summary
Rare earths are valuable resources that play an important role in modern industrial materials. The rare earth elements (REE) absorbed in clay minerals are dissolved in ammonia sulfate solution, which are collected in a leaching liquor pool. The concentration of dissolved REE is a vital factor to evaluate the abundance of REE in leaching liquor and to estimate the contamination of the river near the rare earth ores. We present a new method for quantitative estimation of the concentration of REE dissolved in aqueous media using reflectance spectroscopy. Pure water, rare earth oxide, and ore leaching liquor samples containing various amounts of REE were collected; the reflectance spectra and the concentrations of REE were measured by reflectance spectroscopy and ICP-MS, respectively. The correlation between the spectral absorption depth and the concentration of REE was analyzed, and linear regression models were derived that can be used for estimating the concentration of REE in aqueous media samples
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