In this paper, the multi-walled carbon nanotubes modified screen-printed electrode (MWCNTs/SPE) was prepared and the MWCNTs/SPE was employed for the electrochemical determination of the antioxidant substance chlorogenic acids (CGAs). A pair of well-defined redox peaks of CGA was observed at the MWCNTs/SPE in 0.10 mol/L acetic acid-sodium acetate buffer (pH 6.2) and the electrode process was adsorption-controlled. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods for the determination of CGA were proposed based on the MWCNTs/SPE. Under the optimal conditions, the proposed method exhibited linear ranges from 0.17 to 15.8 µg/mL, and the linear regression equation was Ipa (µA) = 4.1993 C (×10⁻⁵ mol/L) + 1.1039 (r = 0.9976) and the detection limit for CGA could reach 0.12 µg/mL. The recovery of matrine was 94.74%–106.65% (RSD = 2.92%) in coffee beans. The proposed method is quick, sensitive, reliable, and can be used for the determination of CGA.

Deep eutectic solvents (DESs) have the potential to be a lixiviant for the selective processing of metal because of their versatile complexation properties. In this study, the leaching behavior of rare-earth carbonate before and after mechanical activation in chloride–urea–malonic acid, the deep eutectic solvents (ChCl-urea-MA DESs) were investigated. Leaching experiments were employed to investigate the effects of reaction temperature and activation time on the leaching efficiency of the metal, yttrium, in DESs. The leaching efficiency of yttrium was determined to be 85.2% when the activation time was 60 min, the leaching temperature was 80 °C and the leaching time was 12 h. The findings showed that mechanical activation increased the yttrium leaching efficiency from 48.61 to 88.37% by lowering the particle size and increasing the contact area of the reaction. The investigation of the yttrium leaching kinetics revealed that, after mechanical grinding, the apparent activation energy of rare-earth carbonate decreased from 83.88 kJ∙mol⁻¹ to 37.4 kJ∙mol⁻¹, and the leaching process of the sample changed from controlled by chemical reaction to controlled by diffusion in the solid product layer. Mechanical activation combined with DESs was proposed as an eco-friendly, sustainable, and effective alternative to conventional mineral acid leaching and solvent, with advantages such as moderate conditions, reusability of the DESs, and no additional wastewater produced. The findings of the study show this method is a good way to recycle rare-earth metals.

Rare earth is an important strategic resource and a key mineral resource for global competition. As the depletion of primary rare-earth resources increases, a great number of rare-earth secondary resources, such as waste phosphor powder collected from fluorescent lamps, cathode-ray tubes, and other luminescent materials, continue to be generated and accumulated. How to achieve the low-carbon extraction and green and efficient utilization of these resources has become an urgent problem to be solved. In recent years, preliminary enrichment methods, such as flotation, magnetic separation, and adsorption, chemical methods, such as acid leaching and alkaline fusion, external-field-enhanced methods (including mechanical activation, microwave and oxidant, green solvent, etc.), and solvent extraction have been used for the separation and extraction of rare-earth elements (REEs), such as Y, Eu, Ce, Tb, La, and Ga, from waste phosphors. In this article, we systematically summarized the research progress of commonly used separation and extraction methods for REEs in waste phosphor powders, analyzed the advantages, disadvantages, and existing problems of different methods, and proposed potential directions for future research.

In this paper, carbon nanotubes modified screen-printed electrode (CNTs/SPE) was prepared and the CNTs/SPE was employed for the electrochemical determination of antioxidant substance Chlorogenic acids (CGAs). A pair of well-defined redox peak of CGA was observed at the CNTs/SPE in 0.10 mol∙L^-1 acetic acid-sodium acetate buffer (pH 6.2) and electrode process is adsorption-controlled. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) method for the determination of CGA were proposed based on the CNTs/SPE. Under the optimal conditions, the proposed method exhibited linear ranges from 4.73×10^-7 to 4.45×10^-5 mol∙L^-1, the linear regression equation was Ipa(µA) = 4.1993 C (mol∙L^-1)+1.1039 (r = 0.9976) and the detection limit for CGA could reach 3.25×10^-6 mol∙L^-1. The recovery of matrine was 94.74~106.65% (RSD = 2.92%) in coffe beans. The proposed method is quick, sensitive, reliable, and can be used for the determination of CGA.