Self-separation of the adsorbent after recovery of rare-earth metals: Designing a novel non-wettable polymer

Polymeric Materials for Rare Earth Elements Recovery

Rare earth elements (REEs) play indispensable roles in various advanced technologies, from electronics to renewable energy. However, the heavy global REEs supply and the environmental impact of traditional mining practices have spurred the search for sustainable REEs recovery methods. Polymeric materials have emerged as promising candidates due to their selective adsorption capabilities, versatility, scalability, and regenerability. This paper provides an extensive overview of polymeric materials for REEs recovery, including polymeric resins, polymer membranes, cross-linked polymer networks, and nanocomposite polymers. Each category is examined for its advantages, challenges, and notable developments. Furthermore, we highlight the potential of polymeric materials to contribute to eco-friendly and efficient REEs recovery, while acknowledging the need to address challenges such as selectivity, stability, and scalability. The research in this field actively seeks innovative solutions to reduce reliance on hazardous chemicals and minimize waste generation. As the demand for REEs continues to rise, the development of sustainable REEs recovery technologies remains a critical area of investigation, with the collaboration between researchers and industry experts driving progress in this evolving field.

Water-Floating Hydrogel Polymer Microsphere Composites for Application in Hydrological Mining of Cu(II) Ions

Innovative materials and technologies capable of extraction and recovery of technologically relevant metal ions from various water sources, such as lakes, oceans, ponds, or wastewater reservoirs, are in great demand. Polymer beads are among the most well-known solid-phase adsorbents and ion exchangers employed in metal ion recovery. On the other hand, hydrogels are an emerging platform for producing innovative adsorbents, which are environmentally friendly and biocompatible materials. In this work, we take advantage of both technologies and produce a new type of material by loading nanostructured polymer microsphere adsorbent into a PVA matrix to obtain a hydrogel polymer microsphere (HPM) composite in the form of a block. The main role of the poly(4-vinylpyrridine-co-methacrylic acid) microspheres is to adsorb metal ions, such as Cu(II), from model water samples. The secondary role of these microspheres in the hydrogel is to change the hydrogel morphology by softening it and stabilizing it under a foam-like morphology. The foam-like morphology endows these composites with the capability of floating on water surfaces. In this work, we report, for the first time, an HPM composite capable of floating on water surfaces and extracting Cu(II) ions from model water samples. This could enable more environmentally friendly hydrological mining technologies by simply deploying adsorbents on water surfaces for metal ion extraction and recovery, thus eliminating the need for water pumping and mechanical processing steps.

Cryptands on a Solid Support for the Separation of Europium from Gadolinium

With the great demand for europium in green-energy technologies comes the need for innovative methods to isolate the elements. We introduce a solid-liquid extraction method using a 2.2.2-cryptand-modified solid support to separate europium from gadolinium using their differences in electrochemical potential. The method overcomes challenges associated with the separation of those two ions that have similar coordination chemistry in the +3 oxidation state. A competitive adsorption study in the cryptand system between EuII/EuIII and GdIII shows greater affinity for EuII relative to GdIII. After separation from GdIII, Eu was released by oxidizing EuII to EuIII with 99.3% purity. The purity of separated Eu is unaffected by pH between pH 3.0 and 5.5. Overall, we demonstrate that by modifying a solid support with 2.2.2-cryptand, divalent europium can be separated from trivalent gadolinium based on the differences of affinities of 2.2.2-cryptand for the two ions.

Effective recovery of ytterbium through biosorption using crosslinked sericin-alginate beads: A complete continuous packed-bed column study

The recovery of rare-earth from secondary sources is essential for cleaner production. The development of natural biocomposites is promising for this purpose. Sericin is a waste protein from silk manufacturing. The highly polar groups on the surface of sericin facilitate blending and crosslinking with other polymers to produce biocomposites with improved properties. In this work, we investigate ytterbium recovery onto a natural biocomposite based on sericin/alginate/poly(vinyl alcohol) (SAPVA) in packed-bed column, aiming to establish a profitable application for sericin. Effects of flow rate and ytterbium inlet concentration showed that the highest exhaustion biosorption capacity (128.39 mg/g) and lowest mass transfer zone (4.13 cm) were reached under the operating conditions of 0.03 L/h and 87.95 mg/L. Four reusability cycles were performed under the optimum operating conditions using 0.3 mol/L HNO₃. Ytterbium recovery was highly successful; desorption efficiency was higher than 97% and a final ytterbium-rich concentrate (3870 mg/L) was 44 times higher than input concentration. Regenerated beads characterization showed that the cation exchange mechanism plays a major function in continuous biosorption of ytterbium. SAPVA beads also showed higher biosorption/desorption performance for ytterbium than other competing ions. These results suggest the application of SAPVA may be an alternative for large-scale ytterbium recovery.

Impact Dynamics and Freezing Behavior of Surfactant-Laden Droplets on Non-Wettable Coatings at Subzero Temperatures

The present study investigates the impact and freezing behavior of the droplets of surfactant solutions on non-wettable coatings at very low temperatures of -10 to -30 °C. Our goal is to elucidate the critical role of concentration, molecular weight, and ionic nature of surfactants on these phenomena. To achieve this goal, we used sodium dodecyl sulfate (anionic), hexadecyltrimethylammonium bromide (cationic), and n-decanoyl-n-methylglucamine (nonionic) at four concentrations ranging from 0 to 2 × CMC (critical micelle concentration). We captured the impact-freezing of the droplets on superhydrophobic alkyl ketene dimer coatings using a high-speed camera at 5000 frames per second. The results show that the ability of the droplets to spread and retract on the coatings is a function of concentration, ionic nature, and molecular weight of the surfactants, as well as the temperature-dependent viscosity of the solutions. Additionally, surfactant-laden droplets generally demonstrated an accelerated freezing compared to pure water. This might be due to the fact that the presence of surfactants can promote both heterogeneous ice nucleation from within the liquid and a larger solid-liquid interfacial area by filling the air pockets of the surface, leading to enhanced heat transfer. The behavior of the cationic surfactant at certain concentrations was, however, an exception leading to a freezing delay, for which a mechanism will be proposed.

Synthesis and Characterization of Poly(pyrrole-1-carboxylic acid) for Preconcentration and Determination of Rare Earth Elements and Heavy Metals in Water Matrices

Pyrrole was N-functionalized with solid carbon dioxide followed by chemical polymerization to create a new air-stable, granular, and water-insoluble sorbent, poly(pyrrole-1-carboxylic acid) (PPy-CO₂). PPy-CO₂ exhibited enhanced affinity for the sorption of metal ions compared to unfunctionalized PPy due to the incorporation of carboxylate functional groups directly onto the polymer backbone. As a freestanding sorbent material, immobilization to an additional solid support is not needed. Sorption, and therefore preconcentration, occurs simultaneously to achieve efficient removal and recovery of metal ions by a pH-dependent sorption-desorption mechanism. PPy-CO₂ was evaluated on the analytical scale for the solid-phase extraction of a range of metal ions and found to efficiently preconcentrate rare earth elements (REEs), Th, and heavy metals (Cr, Fe, Cd, and Pb), which allowed quantitation by inductively coupled plasma mass spectrometry (ICP-MS). The impact of sorption parameters, such as solution pH, amount of sorbent, and sorption time, and the effect of desorption flow rate for recovery were investigated and optimized using ultrasound-assisted dispersive solid-phase extraction (UAD-SPE) with ICP-MS analysis. Maximum efficiency for sorption and recovery of most metal ions was achieved at a solution pH of 6.0, 10 mg of sorbent, a sorption time of 5 min, and desorption conditions of 1 mL of 2 M nitric acid applied at a flow rate of 0.25 mL min^-1. Detection limits for REEs and Th ranged from 0.2-3.4 ng L^-1 for REEs and Th and 0.9-5.7 ng L^-1 for heavy metals. Linear ranges from 0.1-1000 μg L^-1 for REEs and 0.1-500 μg L^-1 for heavy metals and Th were also observed. PPy-CO₂ successfully preconcentrated and facilitated the determination of the targeted metal ions in water matrices of varying complexity, including tap water, well water, river water, and produced water samples. These results indicate the potential application of PPy-CO₂ for larger-scale recovery and removal of valuable or hazardous metal ions.