Lidija Ćurković

This reprint gathers the fourteen research articles originally published in the Special Issue of Materials titled “Advanced Materials and Processing Technologies”

Waste electrical and electronic equipment (WEEE) is a rapidly growing waste stream rich in precious metals, with gold in particular being concentrated in printed circuit boards and other high-value components. Historically, industrial recycling has relied on pyrometallurgy and non-selective hydrometallurgical leaching. These recovery routes have major drawbacks, including high energy demand, corrosion, the use of toxic reagents, and the complexity of pregnant leach solutions, which complicate downstream gold recovery. This review aims to synthesize recent advances in selective gold recovery from WEEE using a speciation-driven approach. Mechanical pretreatment and physical beneficiation methods are critically assessed as processes for concentrating gold and reducing the amount of material sent to downstream hydrometallurgical leaching. Different lixiviants, from conventional cyanide to halide-based, as well as greener chemistries such as thiosulfate and thiourea, are assessed for gold dissolution from the WEEE stream. Assessment of different extraction methods, including sorbents, ion exchange resins, solvent/ionic liquid, direct reduction/precipitation, and electrochemical recovery, is conducted. The review concludes with guidelines for potential process integration and highlights the need for scalable, reusable lixiviants and sorbent materials validated under realistic multi-metal conditions in real WEEE leachate.

Defect-rich amorphous graphitic carbon nitride prepared within minutes in a household microwave oven exhibits strongly enhanced visible-light-driven degradation of procaine, highlighting a sustainable photocatalyst synthesis.

Climate change mitigation has placed increasing pressure on businesses to adopt sustainable practices, yet the absence of clear rules has led to widespread greenwashing, i.e., misleading claims about environmental benefits. This paper examines the evolution of EU policy responses, with particular focus on the proposed Green Claims Directive, designed to regulate and harmonise environmental claims across Member States. The analysis reviews the historical context of greenwashing, notable corporate scandals, and the rise of both mandatory and voluntary environmental labels such as the EU Energy Label, EU Ecolabel, and EMAS, which, while useful, contribute to consumer confusion due to their variety and inconsistent standards. The Directive aims to strengthen consumer trust by requiring third-party verification and transparent life cycle evidence for claims. However, its implementation faces obstacles, including political negotiations, industry resistance over costs, and concerns for micro-enterprises. Despite delays, the Directive is integral to the European Green Deal, as credible sustainability communication is essential for empowering consumers, ensuring market fairness, and accelerating the transition to a climate-neutral economy.

In this study, the chemical solubility (stability) of yttria-partially stabilized zirconia (2.3Y-TZP) dental ceramics, both glazed (Group 2) and non-glazed samples (Group 1), was evaluated using a modified testing protocol based on ISO 6872:2024. Chemical stability was assessed by measuring ion release with inductively coupled plasma mass spectrometry (ICP-MS) and by analyzing phase composition with X-ray diffraction (XRD). While ISO 6872 prescribes chemical stability testing in a 4 wt.% aqueous acetic acid solution at 80 °C for 16 h, the exposure duration in this study was extended to 768 h (32 days) to allow a more accurate determination of long-term solubility behavior. Additionally, the surface roughness parameters (R_a, R_max, R_z, S_a, S_q) were analyzed and evaluated before and after solubility testing. Kinetic analysis revealed that degradation followed a near-parabolic rate law, with power-law exponents of n = 2.261 for Group 1 and n = 1.935 for Group 2. The corresponding dissolution rate constants were 3.85 × 10⁻⁵ µgⁿ·cm⁻²ⁿ·h⁻¹ for Group 1 and 132.3 µgⁿ·cm⁻²ⁿ·h⁻¹ for Group 2. XRD results indicated that the long exposure to acetic acid induced a partial phase transformation of zirconia from the tetragonal to the monoclinic phase. Under prolonged acetic exposure, the glaze layer on 2.3Y-TZP exhibited significantly higher dissolution, whereas the zirconia (polished, unglazed) showed low ion release. The temporal change in the total amount of dissolved ions was statistically analyzed for Group 1 and Group 2. The samples showed a strong correlation, but ANOVA confirmed significant differences between them.

Zirconia-based ceramics are widely used in dental applications due to their excellent mechanical and chemical properties. The aim of this study was to evaluate the chemi-cal stability of yttria partially stabilized zirconia (Y-TZP) dental ceramics using a modified testing protocol based on ISO 6872. Two sample groups of Y-TZP material were used: Group 1 - pure polished zirconia, and Group 2 - pure polished zirconia with an additional glaze layer. Chemical stability, defined as corrosion resistance, was as-sessed by measuring ion release using inductively coupled plasma mass spectrometry (ICP-MS) and by analysing the phase composition using X-ray diffraction (XRD). While ISO 6872 prescribes chemical stability testing in a 4 wt.% aqueous acetic acid (CH₃COOH) solution at 80 °C for 16 hours, the exposure duration in this study was extended to 768 hours (32 days) to enable more accurate determination of long-term corrosion behaviour. Kinetic analysis revealed that degradation followed a near-parabolic rate law, with power-law exponents of n = 2.261 for Group 1 and n = 1.935 for Group 2. The corresponding corrosion rate constants were 3.85 × 10−5 µgn⋅cm−2n⋅h−1 for Sample 1 and 132.3 µgn⋅cm−2n⋅h−1 for Sample 2. XRD results indicated that the corrosion process led to a partial phase transformation of zirconia from the tetragonal to the monoclinic phase.

Choosing the appropriate cutting tool material is essential for enhancing machining processes because it directly affects product quality, surface finish, dimensional accuracy, tool longevity, and overall efficiency. Different materials are used for cutting tools, i.e., for cutting inserts. Due to their high hardness and high temperature resistance, ceramics cutting inserts allow for increased cutting speeds, resulting in shorter manufacturing times and reduced costs, despite being pricier than traditional cemented carbide and facing certain technical challenges due to their brittleness. Alumina-based ceramics dominate the market, accounting for about two-thirds of usage, followed by silicon nitride and zirconia. This paper provides a comprehensive overview of recent advances in alumina ceramic materials used as cutting inserts, focusing on research conducted in the last five years to optimize static and dynamic mechanical and thermal properties, wear resistance, density, etc. They ways in which the properties are altered through the incorporation of whiskers, nanoparticles, or nanotubes; the modification of the structure; the optimization of sintering parameters; and the application of advanced sintering techniques are demonstrated. The paper also addresses sustainability, environmental impact, and the management of critical raw materials associated with cutting inserts, which pertains to the future development of cutting insert materials.

In this research, an emerging, non-metallic photocatalyst was prepared by the thermal polymerization method from three different precursors: urea, melamine, and three mixtures of melamine and cyanuric acid. Graphitic carbon nitride (g-C₃N₄) samples from urea and melamine were synthesized in a muffle furnace at three different temperatures: 450°, 500°, and 550 °C for 2 h, while the samples made of a mixture of melamine and cyanuric acid (with mass ratios of 1:1, 1:2, and 2:1) were synthesized at 550 °C for 2 h. All the samples were characterized in order to determine their chemical and physical properties, such as crystallite size and structure, and phase composition by the following techniques: Fourier transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS). Nitrogen adsorption/desorption isotherms were used to investigate the Brunauer, Emmett, and Teller (BET) specific surface area and Barrett–Joyner–Halenda (BJH) pore size distribution. Band gap values were determined by diffuse reflectance spectroscopy (DRS). Furthermore, adsorption and photocatalytic degradation of the local anesthetic drug procaine were monitored under UV-A, visible, and simulated solar irradiation in a batch reactor. Kinetic parameters, as well as photocatalytic mechanisms using scavengers, were determined and analyzed. The results of the photocatalysis experiments were compared to the benchmark TiO₂ Evonik Aeroxide P25. The results indicated that the g-C₃N₄ sample synthesized from urea at 500 °C for 2 h exhibited the highest degradation rate of procaine under visible light.