With the widespread use of lithium-ion batteries, the cumulative amount of used lithium-ion batteries is also increasing year by year. Since waste lithium-ion batteries contain a large amount of valuable metals, the recovery of valuable metals has become one of the current research hotspots. The research uses electrometallurgical technology, and the main methods used are cyclic voltammetry, square wave voltammetry, chronoamperometry and open circuit potential. The electrochemical reduction behavior of Ni³⁺ in NaCl-CaCl₂ molten salt was studied, and the electrochemical reduction behavior was further verified by using a Mo cavity electrode. It is determined that the reduction process of Ni³⁺ in LiNiO₂ is mainly divided into two steps: LiNiO₂ → NiO → Ni. Through the analysis of electrolysis products under different conditions, when the current value of LiNiO₂ is not less than 0.03 A, the electrolysis product after 10 h is metallic Ni. When the current reaches 0.07 A, the current efficiency is 77.9%, while the Li⁺ in LiNiO₂ is enriched in NaCl-CaCl₂ molten salt. The method realizes the separation and extraction of the valuable metal Ni in the waste lithium-ion battery.

Secondary zinc oxide (SZO), which comes from the zinc industry, is an important secondary resource of zinc and other valuable metals. In this study, the production feasibility and rationality of a cleaner zinc recovery process using SZO and a hydrometallurgical method were described. Zinc extraction is promoted by the addition of ammonium bicarbonate to a NH₃–H₂O system, and the maximum recovery of zinc could be close to 80% at the optimum leaching conditions of a stirring rate of 400 rpm, an ammonia/ammonium ratio of 7:3, a total ammonia concentration of 4 mol/L, and a liquid/solid ratio of 7 mL/g for 30 min at 35 °C. The kinetics of leaching were modeled using the shrinking core model of constant-size particles, and the rate-controlling step was determined to be the diffusion through the product layer. The apparent activation energy of the reaction was estimated to be 11.04 KJ·mol⁻¹, while the order of reaction with respect to total ammonia concentration was 1.53 and the liquid/solid ratio was 2.26. The analysis results of the initial residue and the leached residue indicated that lead was transferred from PbCl₂ to PbCO₃ and that ZnFe₂O₄ was not leached in the NH₃-NH₄HCO₃-H₂O system.

Steel slag, as industrial solid waste, is difficult to recycle owing to its complex components and poor mechanical properties. However, steel slag can be modified by adding Al₂O₃–SiO₂ through high temperature sintering, which would improve the mechanical properties and expand the scope of its application. The phase changing, morphology evolution and the mechanical properties of the modified steel slag were investigated. The results indicate that the main phase changes to gehlenite occur with increasing temperature. The compressive strength increases to 115 MPa at 1350 °C. The relationship of the quantity of gehlenite and the compressive strength were explored.

The CoCrFeNi system is one of the most important high entropy alloys (HEAs) systems. By adding and adjusting the alloy element components and using different synthesis methods, different phases, organization and microstructure can be obtained, thus improving their properties. In this study, CoCrFeNiTi_x HEAs with various Ti contents (x in molar ratio, x = 0, 0.5, 1.0, 1.5) were fabricated by an electrochemical process by virtue of different oxides. The impacts of different Ti contents on the structure, distribution of elements, mechanical properties and corrosion behavior were researched using XRD, EDX and other testing methods. The bulk CoCrFeNiTi_x (x = 0, 0.5, 1.0, 1.5) HEAs could be obtained through vacuum hot pressing sintering process (VHPS), which had a single-phase FCC structure. The results of the study showed that the bulk CoCrFeNiTi_x exhibited superior ultimate tensile strength (UTS) and hardness, with the UTS of CoCrFeNiTi as high as 783 MPa and the hardness of CoCrFeNiTi_1.5 reaching 669 HV. The corrosion behavior of CoCrFeNiTi_x (x = 0, 0.5, 1.0, 1.5) HEAs in 0.5 M H₂SO₄, 1 M KOH and 3.5 wt% NaCl was improved with addition of Ti. CoCrFeNiTi_x (x = 0, 0.5, 1.0, 1.5) HEAs have great potential for application in the fields of biomedical coating and aerospace, as well as extreme military industry, etc.

With the continuous development of society, the number of spent lithium-ion batteries has also increased, and the recovery of valuable metals such as Ni, Co, and Li has become the main research direction of many scholars. In this paper, the extraction process of lithium that enters the molten salt after LiCoO₂ electrolysis is studied. Oxalic acid and phosphate are added to molten salt containing lithium ions to realize the two-part precipitation method to extract lithium. The influence of pH value, temperature, reaction time, and oxalic acid (or phosphate) addition on the process of oxalic acid calcium removal and phosphate lithium precipitation is analyzed. The results show that the calcium removal rate of oxalic acid has reached 99.72% (Initial conditions: PH = 7.0, T = 70 °C, t = 1.5 h, n(H₂C₂O₄):n(Ca²⁺) = 1.2:1). The precipitation of Li₃PO₄ obtained in the phosphate extraction experiment of lithium is as high as 88.44% (Initial conditions: PH = 8.0, T = 70 °C, t = 1.5 h, n(actual dosage of Na₃PO₄):n(theoretical dosage of Na₃PO₄) = 1.2:1). The obtained lithium phosphate crystals show regular spherical particles, which can be seen by SEM.