Characteristics of Precipitation of Rare Earth Elements with Various Precipitants

Abstract

The effective and selective leaching of rare earth elements (REEs) from various sources is frequently possible in practice by adopting a carefully coordinated strategy incorporating a selective precipitation of these elements from undesired ones in solution. In this study, the behavior of chemical precipitation of REEs with commonly used precipitants such as sulfate, carbonate, fluoride, phosphate, and oxalate was examined using thermodynamic principles and calculations. It was found that the pH of the system has a profound effect on determining particular chemical species of precipitants, which are subsequently responsible for the precipitation of REEs. The role of various anions such as Cl−, NO3−, and SO42− derived from the acid used in the leaching process on the precipitation behavior of REEs was examined. These anions form complexes with REEs and display a very positive effect on the precipitation behavior. The nitrate environment exhibits most conducive to precipitation followed by sulfate and then chloride.

Impacts of Phosphorous Source on Organic Acid Production and Heterotrophic Bioleaching of Rare Earth Elements and Base Metals from Spent Nickel-Metal-Hydride Batteries

“…The reductions in phosphate level indicate occurrence of a chemical reaction between the elements present within the spent battery material and the unutilized phosphorous. REEs have the potential to precipitate with phosphate ions at pH range of 4-6 [41] which resembles the pH range (3.1-6.4) observed during the bioleaching processes in this study. Nevertheless, because of complexity of the bioleaching medium (presence of numerous bacterial metabolites) and hydrolysis and complexation reactions of the solubilized metals, it is hard to make exact predictions about the reaction behavior of the elements in solution [41].…”

“…Even with the spent-medium bioleaching, during which S. pilosus was allowed to grow and produce 10 mM pyruvic acid, no considerable leaching was observed for any of the target elements. This could be due to four different reasons: (1) concentrations higher than 10 mM pyruvic acid are needed; (2) K 2 HPO 4 buffering impedes achieving low pH necessary for proton promoted leaching, (3) absence of metal complexation promoted leaching under these conditions, and/or (4) precipitation of leached metals with phosphorous in the medium [41].…”

Rare Earths (La, Y, and Nd) Adsorption Behaviour towards Mineral Clays and Organoclays: Monoionic and Trionic Solutions

“…The absence of hydrolysis was checked by MEDUSA software calculation (version 16.1); the plots are reported in the Supplementary Information ( Figures S1-S4). According to the literature [34,35], in these experimental conditions, no hydrolysis occurred.…”

Editorial for Special Issue “Leaching of Rare Earth Elements from Various Sources”

“…Preferential precipitation of the dissolved REEs from the leach liquor can be a key to the success of the overall leaching process. Researchers have demonstrated the effective precipitation of REEs using various precipitants [15,16]. The effect of the anions present in the leach liquor has been found to be significant in the precipitation process.…”

“…The effect of the anions present in the leach liquor has been found to be significant in the precipitation process. For example, anions such as Cl − , NO 3 − , and SO 4 2− derived from acids used in the leaching process display a significant effect on the precipitation [15]. Watts and Leong have hypothesized that the distribution coefficient, λ, may be approximated from thermodynamic terms, including the solubility product (K Sp ) of each rare earth oxalate and the stability constant (β 1 ) for the mono oxalato complex of each rare earth.…”