Yankuang ceshi (Nov 2019)
Determination of Rare Earth Elements in Barite-associated Rare Earth Ores by Alkaline Precipitation Separation-Inductively Coupled Plasma-Mass Spectrometry
Abstract
BACKGROUND When inductively coupled plasma-mass spectrometry (ICP-MS) is used to determine the rare earth elements (REE) in the barite-associated light rare earth ores, Ba and light rare earth elements La, Ce, Pr, Nd, Sm, cause severe mass spectral overlap interference to the medium and heavy rare earths. Therefore, under the condition that complete digestion of oress, if the appropriate pretreatment method can be selected to achieve effective separation of the target elements from the matrix, it will be beneficial to reduce mass spectrum interferences. OBJECTIVES To reduce the mass spectrum interferences by establishing a simple and effective pretreatment method for separation of rare earth elements from barium and other coexisting elements in barite-associated rare earth ores. METHODS The barite-associated rare earth ores samples were fused with sodium peroxide and sodium carbonate. After dissolution of the fusion cake, the target REE and the undesired barium were precipitated in triethanolamine solution, but some matrix elements like Si, Fe, Mg, and Al in samples, and most fusion agents, were separated by filtration. The target REE were secondly precipitated in ammonium hydroxide after dissolution of the precipitates by acid, so that Ba, Sr and Ca could be separated from REE. The separation exceeds 96%, so the mass spectrum interferences caused by barium polyatomic ions were effectively reduced. In addition, the interference correction coefficients by measuring the interference concentration at m/z 138-175 of the high concentration lighter rare earths standard single element solution were adopted to account for the oxide and hydroxide overlap problem for the determination of middle and heavier rare earth elements. RESULTS The validity of the method was evaluated by analyses of rare earth ores certified reference materials and the results were in good agreement with certified values (|RE| < 10%). For the actual sample analysis of the barite-associated rare earth ores, the relative standard deviations (n=12) were from 0.5% to 4.6%, which proved that the method can be used to analyze rare earth elements in high-Ba ores. CONCLUSIONS The results demonstrate that this method is both practical and effective for rare earth elements analysis in barite-associated rare earth ores.
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