Cyanide-containing effluents from hydrometallurgical gold extraction pose significant environmental risks due to their high toxicity. This study investigates the detoxification of cyanide-laden tailings from the Altyntau Kokshetau gold extraction facility (Kazakhstan) using sodium percarbonate in alkaline conditions. Employing response surface methodology (RSM) and central composite design (CCD), we optimized key parameters—pH (10–12), sodium percarbonate dosage (1.5–4.0 g), reaction time (10–40 min) and temperature (20–25 °C)—achieving 83.33% detoxification efficiency within 40 min and 99.99% after 8 h, reducing cyanide from 443.2 mg/L to 0.05 mg/L. The process follows biphasic pseudo-first-order kinetics ((k₁ = 0.0517) min^–1 initially, (k₂ = 0.01665) min^–1 subsequently), driven by HO^• radical-mediated oxidation of ${CN}^{-}$ to ${CNO}^{-}$, as described by $({CN}^{-}+H_2{O}_2\to {CNO}^{-}+ H_{2}O$). pH emerged as the dominant factor, optimizing radical stability and ${CN}^{-}$ protonation (pK_a ≈ 9.21) at pH 10. Infrared spectroscopy confirmed the presence of cyanide complexes ($[Au{\left(CN\right)}_2{]}^{-}$, $[Fe{\left(CN\right)}_6{]}^{4-}$) in tailings, underscoring the need for effective treatment. The method ensures compliance with stringent environmental standards (e.g., ICMI limit of 0.2 mg/L), offering a scalable, eco-efficient solution for mitigating the environmental footprint of gold mining operations.

The sorption, structural, and thermal properties of the interpolymer system based on polymethacrylic acid (PMAA) and poly-4-vinylpyridine (P4VP) were studied at different component ratios for the extraction of rhenium (ReO₄⁻) and molybdenum (${\mathrm{M}\mathrm{o}\mathrm{O}}_4^{2-}$) ions from model solutions. The results showed that sorption efficiency depends on both composition and contact time. Systems with molar ratios of 3:3 and 2:4 exhibited the highest activity, reaching more than 90% extraction for rhenium and up to 94% for molybdenum after 48 h. FTIR spectra indicated the involvement of carboxyl and pyridine groups in complex formation with the metal ions, as evidenced by band shifts and the appearance of new absorption features. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) demonstrated that modification of PMAA with P4VP enhances the thermal stability of the system, which is maintained even after desorption. The system with the optimal composition showed structural stability and the ability to regenerate without a notable decrease in sorption capacity. Sorption performance was preserved across a wide pH interval, with maximum values at pH 2–4, which makes the system suitable for hydrometallurgical applications. Comparison with literature data indicates agreement with current approaches to rare-metal recovery, while the PMAA–P4VP system is distinguished by improved stability and potential for further development. These findings provide a basis for the design of selective and environmentally safe processes for rhenium and molybdenum recovery, relevant to the conditions of the Republic of Kazakhstan, where technogenic solutions rich in these metals are available.

This study presents the results of an investigation into the effectiveness of microwave (MW) treatment (1) as a preconditioning method for technogenic raw materials (2) to enhance zinc (3) leaching (4) efficiency. Selective dielectric heating facilitates phase transformations (5), converting sphalerite (ZnS) into zinc oxide (ZnO), which exhibits significantly improved acid leachability. The response surface methodology (RSM) was utilized to evaluate critical operational variables, encompassing sulfuric acid concentration, leaching period, slurry density, and thermal conditions. The obtained results confirm the potential of MW treatment in hydrometallurgical processes, offering a sustainable and energy-efficient alternative for processing technogenic raw materials.

Multilayer hard coatings remain among the most effective engineering solutions for reducing friction and wear and for extending the service life of components operating under high contact loads. However, their practical performance is governed not by multilayering per se, but by the extent to which the selected deposition technology enables reproducible control over three key parameters: layer density and defectiveness, adhesion to the substrate and/or interlayers, and architectural tunability through interface quality. This mini-review systematizes deposition approaches relevant to tribological applications and proposes a generalized classification comprising chemical processes (sol–gel, chemical vapor deposition (CVD), atomic layer deposition (ALD), hydrothermal synthesis, electrodeposition, anodization, and electroless coatings), physical vacuum techniques of the PVD family (magnetron sputtering, cathodic arc deposition, hollow cathode discharge (HCD) ion plating, ion beam assisted deposition (IBAD), among others), as well as hybrid and functional solutions (PVD+CVD, composite, self-lubricating, and nanocomposite systems). It is demonstrated that the selection of a deposition process for multilayer architectures must be based on technological constraints that directly affect interface stability and coating durability, including the deposition temperature window and conformality, interfacial diffusion-induced boundary blurring, residual stresses, and critical defects such as porosity, macroparticles, and growth-related imperfections. Practical guidelines are formulated for correlating “architecture–deposition regime–microstructure–tribological behavior,” and key directions for future research are identified, including interface and defect engineering, targeted hybridization of deposition processes to compensate for intrinsic limitations (conformality, density, adhesion, and interface stability), and the use of predictive modeling validated by comparable tribological testing.

With increasingly stringent requirements for wear resistance and reliability of functional coatings for heavily loaded friction units, a relevant challenge in materials science is to establish the relationships between the parameters of reactive pulsed magnetron sputtering and the tribo-mechanical properties of TiN/CrN multilayer systems. In this study, TiN/CrN multilayer coatings were deposited by reactive pulsed magnetron sputtering using separate titanium and chromium targets. The effect of the nitrogen flow rate (0.20–0.36 L/h) during chromium sputtering on the structure, phase composition, and mechanical and tribological properties of the coatings was investigated at a fixed nitrogen flow rate of 0.08 L/h for titanium. SEM, EDS, and XRD showed that increasing the nitrogen flow rate leads to a non-monotonic change in coating thickness (2.0–2.6 µm), caused by the transition of the chromium target from the metallic to the poisoned sputtering mode. At low N₂ flow rates, a subnitride Cr₂N phase forms in the structure, whereas at the optimal flow rate of 0.32 L/h the coating consists of stable TiN, CrN, and (Cr_0.5Ti_0.5)N phases. The coating nanohardness was 20–23 GPa and the Young’s modulus was 250–300 GPa. The best tribological performance was achieved at a nitrogen flow rate of 0.32 L/h, coefficient of friction μ ≈ 0.5 and a minimum wear rate of 1 × 10⁻⁵ mm³/(m·N), which correlates with the highest H³/E² value. It is shown that independent control of the CrN layer stoichiometry using separate targets can affect the tribo-mechanical properties of the TiN/CrN multilayer system.