Use of electrochemical techniques for the study of solubilization processes of cerium–oxide compounds and recovery of the metal from molten chlorides

Investigation of Rare Earth Element Binding to a Surface-Bound Affinity Peptide Derived from EF-Hand Loop I of Lanmodulin

Bioinspired strategies have been given extensive attention for the recovery of rare earth elements (REEs) from waste streams because of their high selectivity, regeneration potential, and sustainability as well as low cost. Lanmodulin protein is an emerging biotechnology that is highly selective for REE binding. Mimicking lanmodulin with shorter peptides is advantageous because they are simpler and potentially easier to manipulate and optimize. Lanmodulin-derived peptides have been found to bind REEs, but their properties have not been explored when immobilized on solid substrates, which is required for many advanced separation technologies. Here, two peptides, LanM1 and scrambled LanM1, are designed from the EF-hand loop 1 of lanmodulin and investigated for their binding affinity toward different REEs when surface-bound. First, the ability of LanM1 to bind REEs was confirmed and characterized in solution using circular dichroism (CD), nuclear magnetic resonance (NMR), and molecular dynamics (MD) simulations for Ce(III) ions. Isothermal titration calorimetry (ITC) was used to further analyze the binding of the LanM1 to Ce(III), Nd(III), Eu(III), and Y(III) ions and in low-pH conditions. The performance of the immobilized peptides on a model gold surface was examined using a quartz crystal microbalance with dissipation (QCM-D). The studies show that the LanM1 peptide has a stronger REE binding affinity than that of scrambled LanM1 when in solution and when immobilized on a gold surface. QCM-D data were fit to the Langmuir adsorption model to estimate the surface-bound dissociation constant (Kd) of LanM1 with Ce(III) and Nd(III). The results indicate that LanM1 peptides maintain a high affinity for REEs when immobilized, and surface-bound LanM1 has no affinity for potential competitor calcium and copper ions. The utility of surface-bound LanM1 peptides was further demonstrated by immobilizing them to gold nanoparticles (GNPs) and capturing REEs from solution in experiments utilizing an Arsenazo III-based colorimetric dye displacement assay and ultraviolet-visible (UV-vis) spectrophotometry. The saturated adsorption capacity of GNPs was estimated to be around 3.5 μmol REE/g for Ce(III), Nd(III), Eu(III), and Y(III) ions, with no binding of non-REE Ca(II) ions observed.

Photo-electrochemical Osmotic System Enables Simultaneous Metal Recovery and Electricity Generation from Wastewater

Global depletion of natural resources provides an impetus for developing low-cost, environmentally benign technologies for the recovery of valuable resources from wastewater. In this study, we present an autonomous photo-electrochemical osmotic system (PECOS) that can recover a wide range of metals from simulated metal-laden wastewater with sunlight illumination while generating electricity. The PECOS comprises a draw solution chamber with a nickel nanoparticle-functionalized titanium nanowire (Ni-TiNA) photoanode, a feed solution chamber containing synthetic wastewater with an immersed carbon fiber cathode, and a forward osmosis (FO) membrane mounted between the chambers as a separator. Using a Na₂-EDTA anolyte as a draw solution at neutral pH, we demonstrate that a sunlit PECOS achieves copper recovery at a rate of 51 g h^-1 per m^-2 of membrane area from simulated copper-laden wastewater while simultaneously producing a maximum power density of 228 mW m^-2. Moreover, because of the osmotic pressure difference generated by the photo-electrochemical reactions, the PECOS reduces the wastewater volume by extracting fresh water through the FO membrane at a water flux of 0.84 L m^-2 h^-1. We further demonstrate the feasibility of the PECOS in recovering diverse metals from a simulated metal-laden industrial wastewater under sunlight irradiation. Our proof-of-concept PECOS prototype provides a sustainable technological solution that leverages sunlight in an electrochemical osmotic system to recover multiple resources from wastewater.

Regularities of deep deoxidization of molten ionic chlorides in reactive gas atmosphere

The process of the removal of oxide ion admixtures by the action of CCl₄ vapor (carbochlorination) from chloride melts of KCl–NaCl (0.5 : 0.5), BaCl₂–KCl (0.26 : 0.74) and KCl–LiCl (0.41 : 0.59) was studied by a potentiometric method.

Is UV/Ce(iv) process a chloride-resistant AOPs for organic pollutants decontamination?

Negligible AOX formation is observed in UV/Ce(iv)/Cl⁻ process due to the varied reaction pathways in the presence of chloride.

Electrochemical properties of Ce(iii) in an equimolar mixture of LiCl–KCl and NaCl–KCl molten salts

Cyclic voltammetry of Ce(iii) in LiCl–KCl molten salt medium and the morphology of Ce metal deposited by electrochemical deposition.

An investigation into the electrochemical recovery of rare earth ions in a CsCl-based molten salt

A CsCl-based melt, was used as a supporting electrolyte for a fuel cycle in pyrochemical separation, as it has a high solubility for lanthanide oxide. Cyclic voltammetry and square wave voltammetry were carried out to investigate the cathodic reduction of those rare earth ions. The results prove that the cathodic process of La(III) ions dissolved in a CsCl-based melt, with a one-step reduction La(3+)+3e(-)=La, and is similar to those of other reports which have utilised LiCl-KCl or CaCl(2)-KCl molten salt systems. However, for the Ce(III) ions that dissolved in a CsCl-based melt, there is a significant difference when compared with published literature as there are two reduction steps instead of the reported single step Ce(3+)+e(-)=Ce(2+) and Ce(2+)+2e(-)=Ce. In order to explain the novel result, a detailed investigation was focused on the cathodic process of Ce(III) in a CsCl-based melt. The identification of the M-O (M=La, Ce) compounds that are stable in the electrolyte, as well as the determination of their solubility products, were carried out by potentiometric titration using an oxide ion sensor. Furthermore, the E-pO(2-) (potential-oxide ion) diagram for the M-O stable compound was constructed by combining both theoretical and experimental data.

Effect of oxide ions on separation factors of actinides from lanthanides in reductive extraction

The distribution coefficients of Am, Ce, and Eu between the salt and metal phases were measured at 1073 K in a reductive extraction system of equimolar NaCl-KCl melt and liquid Ga. By changing the solute concentrations, it was observed that the distribution coefficients were dependent on the oxide ion concentration in the system, possibly due to the formation of such compounds as AmO+. In addition, the mass balance of Am was possibly affected by the formation and precipitation of its oxychlorides and/or oxides in some runs. Taking these observations into consideration, the separation factor between Am and Ce was found to be around 30 in the present system.