Neutron reflection study of the adsorption of the phosphate surfactant NaDEHP onto alumina from water.

The adsorption of a phosphorus analogue of the surfactant AOT, sodium bis(2-ethylhexyl) phosphate (NaDEHP), at the water/alumina interface is described. The material is found to adsorb as an essentially water-free bilayer from neutron reflection measurements. This is similar to the behavior of AOT under comparable conditions, although AOT forms a thicker, more hydrated layer. The NaDEHP shows rather little variation with added salt, but a small thickening of the layer on increasing the pH, in contrast to the behavior of AOT.We thank BP plc and EPSRC for financial support for this work as well as the ISIS and ILL staff and scientists for the allocation of beam time and technical assistance with NR measurements. We also appreciate Chris Sporikou at Department of Chemistry, University of Cambridge, for help with the surfactant synthesis.This is the final version of the article. It first appeared at http://dx.doi.org/10.1021/la504837

Determination of Rare Earth Elements in Hypersaline Solutions Using Low-Volume, Liquid–Liquid Extraction

Complex, hypersaline brines–including those coproduced with oil and gas, rejected from desalination technologies, or used as working fluids for geothermal electricity generation–could contain critical materials such as the rare earth elements (REE) in valuable concentrations. Accurate quantitation of these analytes in complex, aqueous matrices is necessary for evaluation and implementation of systems aimed at recovering those critical materials. However, most analytical methods for measuring trace metals have not been validated for highly saline and/or chemically complex brines. Here we modified and optimized previously published liquid–liquid extraction (LLE) techniques using bis­(2-ethylhexyl) phosphate as the extractant in a heptane diluent, and studied its efficacy for REE recovery as a function of three primary variables: background salinity (as NaCl), concentration of a competing species (here Fe), and concentration of dissolved organic carbon (DOC). Results showed that the modified LLE was robust to a range of salinity, Fe, and DOC concentrations studied as well as constant, elevated Ba concentrations. With proper characterization of the natural samples of interest, this method could be deployed for accurate analysis of REE in small volumes of hyper-saline and chemically complex brines

Rare Earth Element Distributions and Trends in Natural Waters with a Focus on Groundwater

Systematically varying properties and reactivities have led to focused research of the environmental forensic capabilities of rare earth elements (REE). Increasing anthropogenic inputs to natural systems may permanently alter the natural signatures of REE, motivating characterization of natural REE variability. We compiled and analyzed reported dissolved REE concentration data over a wide range of natural water types (ground-, ocean, river, and lake water) and groundwater chemistries (e.g., fresh, brine, and acidic) with the goal of quantifying the extent of natural REE variability, especially for groundwater systems. Quantitative challenges presented by censored data were addressed with nonparametric distributions and regressions. Reported measurements of REE in natural waters range over nearly 10 orders of magnitude, though the majority of measurements are within 2–4 orders of magnitude, and are highly correlated with one another. Few global correlations exist among dissolved abundance and bulk solution properties in groundwater, indicating the complex nature of source-sink terms and the need for care when comparing results between studies. This collection, homogenization, and analysis of a disparate literature facilitates interstudy comparison and provides insight into the wide range of variables that influence REE geochemistry

Development and Assessment of Different Hydrometallurgical Processes for Sustainable Recovery of Rare Earths from Spent NdFeB Magnets

The utilization of NdFeB magnets is extensive in cutting-edge technologies such as hybrid electric vehicles and wind turbines. These magnets possess a substantial REE (Rare Earth Elements) content, approximately 30%, which significantly surpasses the concentration found in natural REE ores. Due to their pronounced economic significance and the associated supply risks stemming from limited primary resources, REEs are classified as critical metals. With the NdFeB permanent magnet sector experiencing an annual growth rate of 20%, the recycling of end-of-life magnets emerges as a highly effective strategy for mitigating challenges related to the supply of essential raw materials. In the current investigation, three distinct processes have been developed to recover REEs from spent wind turbine magnets. These processes encompass (1) oxidation roasting-acid leaching, (2) chlorination roasting-water leaching, and (3) electrochemical dissolution. Optimization of process parameters has been meticulously undertaken for each of these methods to achieve the production of high-purity rare earth oxide (>99%). Furthermore, a comparative evaluation has been conducted, taking into account energy efficiency and environmental sustainability, to determine the most viable approach for the sustainable recovery of REEs from spent NdFeB magnets

Effects of Ligand Chemistry and Geometry on Rare Earth Element Partitioning from Saline Solutions to Functionalized Adsorbents

Rare earth elements (REE) are elements that drive the development of new technologies in many sectors, including green energy. However, the supply chain of REE is subject to a complex set of technical, environmental, and geopolitical constraints. Some of these challenges may be circumvented if REE are recovered from naturally abundant alternative sources, such as saline waters and brines. Here, we synthesized and tested aminated silica gels, functionalized with REE-reactive ligands: diethylenetriaminepentaacetic acid (DTPA), diethylenetriaminepentaacetic dianhydride (DTPADA), phosphonoacetic acid (PAA), and N,N-bisphosphono­(methyl)­glycine (BPG). A suite of characterization techniques and batch adsorption experiments were used to evaluate the properties of the functionalized silica adsorbents and test the REE-uptake chemistry of the adsorbents under environmentally relevant conditions. Results showed that BPG and DTPADA yielded the most REE-reactive adsorbents of those tested. Moreover, the DTPADA adsorbents demonstrated chemical and physical robustness as well as ease of regeneration. However, as in previous studies, amino-poly­(carboxylic acid) adsorbents showed limited uptake at midrange pH and low-sorbate concentrations. This work highlighted the complexity of intermolecular interactions between even moderately sized reactive sites when developing high-capacity, high-selectivity adsorbents. Additional development is required to implement an REE recovery scheme using these materials; however, it is clear that BPG- and DTPADA-based adsorbents offer a highly reactive adsorbent warranting further study

Effects of Ligand Chemistry and Geometry on Rare Earth Element Partitioning from Saline Solutions to Functionalized Adsorbents

Rare earth elements (REE) are elements that drive the development of new technologies in many sectors, including green energy. However, the supply chain of REE is subject to a complex set of technical, environmental, and geopolitical constraints. Some of these challenges may be circumvented if REE are recovered from naturally abundant alternative sources, such as saline waters and brines. Here, we synthesized and tested aminated silica gels, functionalized with REE-reactive ligands: diethylenetriaminepentaacetic acid (DTPA), diethylenetriaminepentaacetic dianhydride (DTPADA), phosphonoacetic acid (PAA), and N,N-bisphosphono­(methyl)­glycine (BPG). A suite of characterization techniques and batch adsorption experiments were used to evaluate the properties of the functionalized silica adsorbents and test the REE-uptake chemistry of the adsorbents under environmentally relevant conditions. Results showed that BPG and DTPADA yielded the most REE-reactive adsorbents of those tested. Moreover, the DTPADA adsorbents demonstrated chemical and physical robustness as well as ease of regeneration. However, as in previous studies, amino-poly­(carboxylic acid) adsorbents showed limited uptake at midrange pH and low-sorbate concentrations. This work highlighted the complexity of intermolecular interactions between even moderately sized reactive sites when developing high-capacity, high-selectivity adsorbents. Additional development is required to implement an REE recovery scheme using these materials; however, it is clear that BPG- and DTPADA-based adsorbents offer a highly reactive adsorbent warranting further study