Effect of Anions on the Solubility of Rare Earth Element-Bearing Minerals in Acids
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The effect of anions such as sulfate, chloride, and nitrate on the solubility of rare earth element-bearing phosphates and fluoro-carbonates has been examined using relevant thermodynamic data. The study has found that these anions have significant influences on the overall dissolution of rare earth elements (REEs) from various sources in the aqueous media. The thermodynamic calculations in this study have indicated that the speciation of REEs with the anions tends to increase the overall solubility of the REE-bearing minerals. However, in some cases, strong precipitation of REEs with some of these anions causes an adverse effect on the solubility of these elements. It has been found that sulfate ion has the most pronounced effect on the solubility compared to nitrate and chloride, in which the latter two acids exhibited almost identical results. The calculated results have indicated that REE-oxide (hydrated) is the easiest compound to dissolve, followed by carbonate, phosphate, fluoride, sulfate, fluoro-carbonate, and oxalate in that order.
KeywordsSpeciation Rare earth elements Cut-off-pH Solubility Sulfate precipitation Leaching
The author would like to express his thanks to Dr. Jim Gebhardt for his valuable comments on the paper and also to Dr. Rina Kim for sharing some of thermodynamic data.
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Conflict of Interest
The author declares that there is no conflict of interest.
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