Exploring more efficient and low-cost electrocatalysts to replace platinum (Pt) is highly desired to promote the practical hydrogen production through water splitting. Herein, a facile and effective strategy is proposed to fabricate self-standing Al₃Ni₂/Ni electrode with controlled phase composition and surface morphology, which is obtained by one-step electrochemical reduction of Al³⁺ on commercially available nickel in eutectic NaCl-KCl melt. Different from previously reported approaches, uniform Al₃Ni₂ monolith catalyst can directly grow onto Ni substrate. The deposit possesses unique three-dimensional (3D) cauliflower-like morphology comprising of nano- and microparticles due to the rapid nucleation rate during molten salt electrolysis. The as-fabricated Al₃Ni₂/Ni electrode can be directly used as the cathode to catalyze Hydrogen evolution reaction (HER). Impressively, it exhibits remarkable HER activity comparable to commercial Pt, including a low overpotential of 83.4 mV for a current density of 10 mA cm⁻², a small Tafel slope of 40.7 mV dec^-1, and excellent long-term stability over 36 h of continuous HER operation in 0.5 M H₂SO₄ solution. The intrinsic catalytic ability of Al₃Ni₂ with the unique hierarchical structure of nano/microsized grains can offer multiple effects, including massive exposed active sites, enhanced charge transfer and mass transport, and fast gas releasing that synergistically contribute to improving the electrocatalytic performance of HER. This work represents a highly promising approach to the design and one-step controllable fabrication of efficient and self-standing base metal electrode for electrocatalytic hydrogen production.

In the present study, a novel process for effective recoveries of Te and Cu from copper telluride from anode slime processing in copper smelters was proposed. The process consists of two hydrometallurgical steps of atmospheric alkaline leaching for Cu and Te separation, and TeO₂ precipitation with H₂SO₄ for Te recovery. The effects of NaOH concentration, liquid to solid ratio, temperature, H₂O₂ to Cu₂Te mole ratio, and reaction time on the dissolution behavior of tellurium were investigated. A Te leaching efficiency of about 91% was obtained under the optimal experimental conditions. The results of thermodynamic and kinetic analysis indicate that a lower temperature is favorable for the dissolution of Te, and mass transfer inside the solid particle is the rate-determining step. In addition, a mechanochemical-assisted leaching was conducted, by which Te leaching efficiency was enhanced to approximately 93% with ball milling at 180 rpm for 5 h. After Te leaching, H₂SO₄ was utilized to adjust the pH value of the Te-containing alkaline leach solution to 4.5 for TeO₂ precipitation. The crystallization of TeO₂ can be completed by reacting for 1 h and the overall tellurium recovery has reached nearly 90%.

The electrochemical behavior of Dy(III) and its co-reduction process with Zn(II) on a tungsten electrode were studied in eutectic NaCl-KCl melts at 700 °C by using a series of electrochemical techniques. The results indicate that the reduction of Dy(III) to Dy(0) is a diffusion controlled quasi-reversible process through a one-step reaction of exchanging three electrons. The diffusion coefficient of Dy(III) was calculated to be 1.7 × 10-5 cm2 s-1. Furthermore, the co-reduction of Dy(III) and Zn(II) on the tungsten electrode makes Dy(III) be reduced at more positive potentials due to the formation of various Dy-Zn intermetallic compounds. The electromotive force measurements were performed to determine the thermodynamic properties of the Dy-Zn intermetallic compounds, including the activities and relative partial molar Gibbs free energies of dysprosium in the two-phase coexisting state, as well as the standard formation Gibbs energies of Dy-Zn intermetallic compounds. Finally, potentiostatic electrolysis at -2.0 V was carried out in molten NaCl-KCl-DyCl3(1.0 mol%)-ZnCl2(1.0 mol%) at 700 °C for 11 h to prepare Dy-Zn alloy. X-ray diffraction and scan electron micrograph - energy dispersive spectrometry analyses showed that the obtained Dy-Zn alloy mainly comprised of DyZn2, as well as the minor phases of Dy2Zn17, DyZn3 and DyZn.

Copper telluride is a sort of solid waste generated from copper anode slime processing, from which the recovery of copper and particularly the high-value element of tellurium always encounter technical difficulties due to the complex physicochemical properties of tellurium. In this study, an efficient and compact process for copper telluride recycling has been developed. Efficient separation of tellurium and copper from copper telluride was achieved through a pressure oxidizing alkaline leaching process under the optimal conditions of 5 mol/L for NaOH concentration, 5:1 for liquid to solid ratio, 150 °C for temperature, 0.7 Mpa for system pressure, and 2 h for reaction time, by which over 95% of tellurium was selectively dissolved in the solution and copper was enriched in the solid phase mainly in the form of copper oxides. Tellurium was subsequently recovered as TeO₂ by neutralization of the alkaline leaching solution with sulfuric acid to pH 4.5, delivering a TeO₂ precipitation efficiency of over 95%. In general, the masses of tellurium and copper balanced well in both the liquid and solid phases for each step, and the overall recovery efficiencies of Te and Cu reached as high as approximately 91% and 98%, respectively.

Thallium is an emerging pollutant reported in wastewater along with the increasing mining and smelting of thallium-containing ores in recent years. The complete removal of Tl(I) from wastewater is of significant emergency due to its high toxicity and mobility, however, Tl(I) removal is always confronted with numerous technical difficulties because of the extremely low Tl(I) concentration in wastewater and the disturbances of many accompanying impurity ions. Adsorption is currently the most widely used method for Tl(I) removal on industrial scale and varied kinds of adsorbents such as Prussian blue analogues, biosorbents, and metal oxides have been developed. However, the adsorption process of Tl(I) is always affected by the co-existing cations, resulting in low Tl(I) removal efficiency. Recently, the development of a variety of novel adsorbents or ion sensors based on macrocyclic compounds for enrichment and accurate determination of trace Tl(I) in aqueous solutions exhibits great potential for application in Tl(I) removal from wastewater with high selectivity and process efficiency. This paper provides an overview of the adsorption methods for Tl(I) removal from wastewater with emphasis on complexation properties between varied types of adsorbents and Tl(I). Future directions of research and development of adsorptive Tl(I) removal from industrial wastewater are proposed.

Waste aluminate phosphor is a valuable secondary resource of rare earth elements (REEs). However, Ce and Tb in aluminate green phosphor can hardly be extracted by direct leaching in an inorganic acid. Therefore, Na₂CO₃ assisted roasting is adopted to decompose the stable spinel structure of Ce_0.67Tb_0.33MgAl₁₁O₁₉ in the present work and to achieve the transformation of REEs to simple oxides. Based on the thermodynamic calculations, systematic experiments of thermal decomposition have been conducted. The thermal decomposition behavior, phase evolution, valence state change, variations in micro and macro morphology of the green phosphor during Na₂CO₃ assisted roasting were examined by using TG-DSC/MS, XRD, XPS, SEM/EDS analyses. The results indicated that the green phosphor began to react with solid Na₂CO₃ at 800 °C, and the reaction was dramatically accelerated with temperature rising above 851 °C. At about 1000 °C, Ce_0.67Tb_0.33MgAl₁₁O₁₉ could completely decomposed into CeO₂, Tb₂O₃ and MgO by roasting in an equivalent mass of Na₂CO₃ for 2 h, while α-Al₂O₃ was hardly attacked in roasting. The decomposition mechanism of Ce_0.67Tb_0.33MgAl₁₁O₁₉ in molten Na₂CO₃ could be depicted by the unreacted shrinking core model, and the reaction rate constant was estimated at approximately nanometers per second. The synergistic effect of cation-oxoanion ensures the successful extraction of CeO₂ and Tb₂O₃ from the green phosphor via Na₂CO₃ assisted roasting method. The converted CeO₂ and Tb₂O₃ can be extracted by using chlorination roasting and separated from non-REE residues. According to these investigations, a new efficient process technology is proposed for sustainable recycling of waste phosphor.

Design of new adsorbents for complete removal of thallium(I) from wastewater is of significant importance. Based on the theory of binding ability between crown ether and metal ion, a kind of Tl(I)-selected crown ether, thio-18-crown-6 ether, was designed. Subsequently, modeling calculations were performed to investigate the microscopic interaction between 18-crown-6 ether and its sulfur-substituted derivatives with Tl⁺. The results showed that thio-18-crown-6 ether generally showed higher affinity to Tl⁺ than 18-crown-6. The stabilities of these complexes ranked in an order of 5S-18C6 > 4S-18C6(II) > 2S-18C6(I) > 2S-18C6(II) > 6S-18C6 > 3S-18C6 > 18C6 > 1S-18C6. The binding energies of 5S-18C6 with free Zn²⁺, Pb²⁺, Cu²⁺, and Cd²⁺, which are usually impurity ions in thallium-containing wastewater, were more negative than with Tl⁺, indicating more affinity of 5S-18C6 toward these free two-valence ions. However, after the influence of solvent (water) was taken into account, 5S-18C6 showed fairly high selectivity to Tl(I) over Zn²⁺, Pb²⁺, Cu²⁺, and Cd²⁺. Therefore, 5S-18C6 should be a proper compound which has the promising potential to be adopted for the complete and selective removal of Tl(I) from wastewater. Further synthesis and adsorption experiments are needed to verify this prediction.

The electrochemical behavior of yttrium and its co-deposition with aluminum were investigated by several transient electrochemical techniques on a tungsten electrode at 973K in NaCl-KCl eutectic melts. The results reveal that the reduction of Y(III) in NaCl-KCl-YCl₃ melts is a one-step process with three-electron exchanged and the reaction is a quasi-reversible diffusion-controlled process at low scan rates (0.05∼0.5 V/s). The calculated diffusion coefficient is approximately 2.8 × 10−⁵cm²/s. After AlCl₃ was introduced into the melts, cyclic voltammetry and open circuit chronopotentiometry showed the formation of two Y-Al intermetallic compounds, indicating that under-potential deposition of yttrium occurred on tungsten electrode covered with liquid Al. The electromotive force was measured at 973K to determine the thermodynamic properties of Y-Al intermetallic compounds, such as the activity of Y in the two-phase coexistence state, relative partial molar Gibbs energies, as well as the standard Gibbs energies of Y-Al intermetallic compounds. Finally, potentiostatic electrolysis was conducted to prepare Y-Al alloys from molten NaCl-KCl-YCl₃ (1.5 mol%)-AlCl3 (1.5 mol%) by the co-reduction method. The cathodic alloys were characterized using X-ray diffraction (XRD) and scan electron micrograph (SEM)-energy dispersive spectrometry (EDS) and the results indicated that the obtained alloys were mainly composed of YAl₂, as well as YAl₃ and YAl phases. The Y-rich phase intermetallic compound YAl, formed in the later period of electrolysis just when the concentration of AlCl₃ is fairly low.

In the present paper, a detailed study of the redox behavior of zirconium in the eutectic LiF-NaF system was carried out on an inert molybdenum electrode at 750 °C. Several transient electrochemical methods were used such as cyclic voltammetry, square wave voltammetry, chronopotentiometry, and open circuit voltammetry. The reduction of Zr (IV) was found to follow a two-step mechanism of Zr (IV)/Zr (II) and Zr (II)/Zr at the potentials of about −1.10 and −1.50 V versus Pt, respectively. The theoretical evaluations of the number of transferred electrons according to both cyclic voltammetry and square wave voltammetry further confirmed the Zr reduction mechanism. The estimations of Zr (IV) diffusion coefficient in the LiF-NaF eutectic melt at 750 °C through cyclic voltammetry and chronopotentiometry are in fair agreement, as to be approximately 1.13E-5 and 2.42E-5 cm²/s, respectively.