Search Results (339)

Spent automotive catalysts represent an important secondary resource for platinum group metals, offering environmental and economic advantages over primary mining. This review evaluates bioleaching-based recovery strategies of these metals as sustainable alternatives to conventional pyrometallurgical and hydrometallurgical processing. The cyanogenic bioleaching using Chromobacterium violaceum, Pseudomonas fluorescens, and Bacillus megaterium, and acidophilic bioleaching using Acidithiobacillus spp. for washcoat degradation and base-metal removal are discussed through the one-step, two-step, spent-medium, and decoupled systems. The analysis shows progressive improvement of recovery as process separation increases. Sequential pretreatment involving ultrasound-assisted acid leaching, thermal oxidation, and pressure-enhanced processing improved recovery by removing competing base metals and increasing PGM accessibility. Kinetic analyses indicate that diffusion through the porous catalyst support matrix becomes the dominant rate-controlling mechanism at high conversion, which impacts reactor design. Despite sustainability potential, industrial implementation remains constrained by low pulp density, cyanide stability, reactor productivity, and scale-up limitations. Routes to commercialisation require feasibility studies of process designs that integrate viable process flow diagrams combining pretreatment, biological lixiviant generation, intensified bioleaching, and downstream metal purification. Full article

Proton exchange membrane (PEM) electrolyzers and fuel cells could substantially increase demand for iridium (Ir) and platinum (Pt), two platinum-group metals (PGMs) with concentrated primary supply chains. This study evaluates secondary Ir and Pt supply from end-of-life PEM technologies using a scenario-based material-flow analysis for global and U.S. markets from 2020 to 2050. Annual metal demand is estimated from U.S. Department of Energy annual PEM manufactured-capacity inputs, which include new and replacement systems, and from catalyst loading rates. Secondary supply is estimated using distributed lifetimes, collection efficiency, technical recovery efficiency, recycling delay, loss accounting, remaining primary requirement, and surplus. Under the central practical case, recovered Ir supplies 16.9% of global and 3.8% of U.S. PEM electrolyzer Ir demand in 2050. Recovered PEM electrolyzer Pt supplies 32.2% of global and 7.3% of U.S. demand, while recovered PEM fuel-cell Pt supplies 75.1% of global and 51.2% of U.S. demand. Sensitivity and uncertainty results show that recovery outcomes depend strongly on collection performance, recycling delay, technical recovery, catalyst loading, and capacity-input assumptions. PEM recycling can reduce future primary PGM requirements, especially for Pt, but cannot eliminate primary Ir demand during rapid PEM electrolyzer scale-up. Full article

Precious metal nanoparticles (PMNPs), particularly silver, gold, palladium, and platinum nanoparticles, have attracted considerable attention owing to their unique physicochemical properties and broad applications in catalysis, environmental remediation, and biomedicine. Conventional physical and chemical synthesis methods often require substantial energy input, harsh reaction conditions, and generate large volumes of metal-containing wastewater, raising concerns regarding sustainability and environmental impact. Microbial synthesis provides a sustainable alternative by using microorganisms as natural biofactories to convert toxic precious metal ions into valuable nanoparticles under mild conditions. This review summarizes recent advances in the microbial synthesis of PMNPs (Bio-PMNPs), focusing on biosynthetic mechanisms in bacteria, algae, and fungi. Bio-PMNPs formation involves both extracellular and intracellular reduction processes, coupled with electron transfer mediated by reductases and other redox-active biomolecules. Functional groups present on microbial cell walls, as well as proteins, polysaccharides, enzymes, and other metabolites, play important roles in the adsorption, reduction, stabilization, and growth of nanoparticles. We further highlight the applications of Bio-PMNPs in antimicrobial activity, cancer therapy, pollutant degradation, heavy-metal removal, and catalytic enhancement of organic synthesis. Despite substantial progress, challenges remain in controlling nanoparticle size and morphology, elucidating biosynthetic mechanisms, and achieving large-scale production. Future integration of synthetic biology, metabolic engineering, and process optimization is expected to improve the controllability, stability, scalability, and biosafety of Bio-PMNPs production. Full article

The rapid expansion of hydrogen technologies has intensified the demand for platinum group metals (PGMs), particularly platinum (Pt) and iridium (Ir). Proton exchange membrane fuel cells (PEMFCs) and proton exchange membrane water electrolyzers (PEMWEs) rely on PGMs and fluoropolymer membranes such as Nafion, generating increasing volumes of end-of-life (EoL) membrane electrode assemblies (MEAs). Conventional recycling routes are often energy-intensive, hazardous and limited in polymer recovery. In this study, a closed-loop hydrometallurgical recycling route is assessed through a life cycle assessment (LCA), supported by primary experimental data from optimized recycling trials. Mechanical delamination enabled separation of catalyst layers while preserving membranes, followed by a chlorine-based hydrometallurgical process operating under mild conditions. Leaching efficiencies exceeded 99% for Pt and 80% for Ir, demonstrating the feasibility of metal recovery. Two LCA models were developed: (i) a gate-to-gate recycling model for EoL MEAs and (ii) a cradle-to-gate manufacturing model comparing virgin and recycled Pt. Results showed that substituting virgin Pt with recycled Pt reduced the global warming potential of MEA manufacturing by up to 70%. The analysis also identified electricity demand and Nafion membrane waste as key environmental hotspots. Overall, the study highlights the potential of closed-loop recycling to enhance circularity in hydrogen technologies. Full article

Platinum group metals (PGMs) play a key role in many industries. However, the growing demand for PGMs, the systematic decline in their natural resources, and the generation of large amounts of waste, constituting a secondary source, are closely related to the search for effective and environmentally safe methods for their separation. Although solvent extraction (SX) processes, long used to extract PGMs from various ores/waste leachates, typically allow for effective separation of these valuable metals, they rely primarily on the use of organic solvents, many of which are environmentally hazardous. Therefore, recent research efforts have focused, among others, on the utilization of potentially “greener” chemicals, such as ionic liquids (ILs) and deep eutectic solvents (DESs). Due to their tunable properties to specific applications, these chemicals usually enable not only efficient (often >90%) but also selective and more eco-safe separation of PGMs from various matrices. This review concerns the latest developments in the SX of PGM ions from aqueous solutions and suspensions using ILs and DESs (e.g., as extractants, solvents, and leaching agents), taking into account their most important advantages, limitations, and potential impact on the environment. IL- and DES-based SX methods fit into the green chemistry trend and are consistent with sustainable development goals. Full article

Platinum group metals (PGM) are essential for clean-energy technologies, including proton exchange membrane (PEM) electrolyzers for hydrogen production and PEM fuel cells for hydrogen use, as well as catalytic, electronic, and advanced industrial applications. However, their supply is exposed to geological concentration, co-product dependence, and market volatility. This study evaluates the medium-term cost-based accessibility of known primary PGM resources using a cumulative availability curve. The analysis combines resource estimates and allocated production-cost data for 61 known PGM-bearing deposits and projects, with costs expressed in 2022 USD per metric ton of combined PGM output. Because PGM deposits differ in ore type, processing route, and co-product setting, the results are interpreted by deposit cluster rather than only by country or aggregate cost threshold. The low-cost portion of the curve is dominated by Ni–Cu sulphide by-product systems, but this cluster represents only 1.87% of the compiled resource base. In contrast, UG2/Merensky/Great Dyke reef-type systems account for 72.95%, and Platreef/Northern Limb and Platreef-type systems account for 19.82%. Thus, most known primary PGM resources occur outside the low-cost by-product segment. Cluster-weighted PGM basket-price benchmarks are used instead of individual metal-price comparisons. Several cluster-level cost ranges fall below or near indicative April 2025 basket-price benchmarks, but these comparisons are not project-level profitability tests. Overall, the cumulative availability curve provides a deposit-cluster-based framework for evaluating known primary PGM availability and informing critical-material policy, recycling strategy, supply-chain planning, hydrogen-technology deployment, and responsible resource development. Full article

The clinical success of cisplatin has significantly spurred the exploration of new organometallic complexes in oncology. In this quest, repurposing of auranofin as an anticancer agent has diverted the research interest from platinum to gold complexes, as gold offers unique chemical features; among them, thioredoxin reductase (TrxR) inhibition is one of the most extensively studied anticancer pathways. In this study, we have compiled the major ligand modifications reported for gold(I) complexes and categorized them into various groups, which include sulfur-based ligands, nitrogen-containing heterocyclic ligands, carbon-derived ligands, and N-heterocyclic carbene-based ligands. Also, a few structurally distinct ligands, including propargyl-, allene-, tricarbene-, and urea-functionalized NHC frameworks, have further extended structural diversity and functional potential. The in vitro evaluation of these newly synthesized gold complexes against various cancer cell lines exhibited enhanced biological potential compared to conventional metal complexes. Comparative evaluation of the reported cytotoxicity data revealed distinct structure–activity relationships among different ligand classes, with phosphine-carbon donor and bis-NHC frameworks emerging as the most promising ligand for achieving potent anticancer activity, highlighting the critical role of ligand design in modulating anticancer activity. In addition, the use of bioactive pharmacophores derived from natural products and active pharmaceuticals has emerged as a promising design strategy for developing multitarget gold(I) complexes with enhanced therapeutic efficacy. Among the reviewed compounds, complex 68 containing a bis-NHC ligand exhibited the highest potency against HL-60 leukemia cells (GI₅₀ = 0.017 μM), while complex 49 bearing a carbon-donor ligand demonstrated remarkable activity against A549 lung cancer cells (IC₅₀ = 0.02 μM). Several other gold(I) complexes also exhibited submicromolar activity against diverse cancer cell lines, further emphasizing the importance of rational ligand engineering in enhancing anticancer efficacy. Collectively, gold(I) complexes have emerged as a promising class of anticancer agents, and the comparative evaluation presented herein provides a valuable framework for identifying potent ligand scaffolds and guiding the rational development of next-generation gold-based therapeutics. Future advances in ligand engineering may facilitate targeted drug delivery, controlled release, and multi-mechanistic therapeutic strategies to overcome toxicity and drug resistance while enhancing therapeutic efficacy. Full article

Platinum and palladium nanoparticles (Pt- and Pd-NPs) were synthesized using a green reduction approach with ascorbic acid (AA) or saponin from Quillaja bark (Qb) as reducing agents and stabilized with conventional polymers (PVP, polyvinylpyrrolidone, PEG, polyethylene glycol) or natural surfactants (CG (coco glucoside), Qb). The influence of stabilizer type on reduction efficiency, particle size, and colloidal homogeneity was investigated. Pt-NPs exhibited consistently high reduction efficiencies (>87%) in all systems, whereas Pd-NPs showed lower efficiencies and greater sensitivity to synthesis conditions. AFM and DLS analyses confirmed the formation of particles within the nanometric range. In AA-based systems, Pt-NPs were generally smaller than Pd-NPs, while the opposite trend was observed in Qb-based systems. Natural surfactants provided effective NP stabilization, low values of polydispersity index (PdI), good size control, and stable nanostructures. The results demonstrated that biosurfactant-based stabilizers, particularly CG and Qb, can successfully replace synthetic polymeric stabilizers in the green synthesis of noble metal NPs, supporting the development of more sustainable and environmentally friendly synthesis approaches. Full article

Quinoline derivatives constitute a privileged class of nitrogen-containing heterocycles with extensive applications in medicinal chemistry, agrochemicals, materials science, and functional organic materials. Owing to their broad biological and industrial relevance, the development of efficient, selective, and sustainable synthetic methodologies for quinoline construction remains an active area of research. This review provides a comprehensive overview of recent advances in quinoline synthesis, with particular emphasis on catalytic strategies aligned with the principles of green and sustainable chemistry. Classical transformations, including the Friedländer, Skraup, and Povarov reactions, are revisited in the context of modern catalytic developments that improve reaction efficiency, substrate scope, selectivity, and environmental compatibility. Special attention is devoted to homogeneous and heterogeneous catalytic systems based on both platinum-group and earth-abundant transition metals, highlighting the growing importance of borrowing-hydrogen and acceptorless dehydrogenative coupling methodologies. Recent progress in nanocatalysis, photocatalysis, multicomponent reactions, ionic-liquid-mediated transformations, and metal-free protocols is also critically discussed. Furthermore, solvent-free processes, microwave-assisted synthesis, and recyclable catalytic systems are examined as practical approaches toward minimizing waste generation and energy consumption. Mechanistic aspects, catalytic design principles, substrate limitations, and sustainability metrics are evaluated throughout the review to provide a critical perspective on current methodologies. Collectively, the advances summarized herein demonstrate the rapid evolution of quinoline synthesis toward more atom-economical, environmentally benign, and operationally efficient processes, while also identifying future opportunities for the development of next-generation catalytic platforms for quinoline-based heterocycle construction. Full article

Platinum group metals (PGMs: Pt, Pd, Rh, Ru, Os, Ir) are critical strategic metals. Spent automotive catalysts (SACs) represent one of the most significant secondary sources of PGMs, and their recovery is essential for alleviating the supply–demand imbalance. In the recycling chain, pyrometallurgical processing of SACs generates Fe-Si-based alloy concentrates (termed Fe−Si−PGMs), serving as an important yet challenging intermediate resource for PGM recovery. This review first summarizes the pyrometallurgical and hydrometallurgical processes used for recovering PGMs from SACs, before shifting its focus to the treatment technologies for PGMs in Fe–Si–PGMs alloy. These techniques, including direct extraction, extraction following desilication (via alkaline roasting, slagging, or hydrometallurgical routes), and in situ mechanochemical extraction, are critically evaluated in terms of their advantages and limitations. Furthermore, given that the accurate quantification of trace-level yet high-value PGMs represents another key challenge in the recovery chain due to complex sample matrices, this work systematically outlines and compares the analytical methods commonly employed, such as fire assay, spectroscopic and mass spectrometric techniques, electrochemical methods, and alkali fusion. Finally, several recommendations are provided regarding PGM recovery from SACs, with emphasis on Fe−Si−PGMs alloy processing and analytical methods for PGMs. Full article

Due to its extensive industrial applications and high market prices, as well as low mining yield, the recovery of rhodium from various secondary resources is becoming increasingly urgent for addressing its supply issues. Generally, rhodium is extracted last from the leaching solutions containing other platinum group metals and base metals. The lengthy processing flow led to the inevitable yield loss of rhodium. Compared to the conventional extraction process, selective preferential separation and extraction of rhodium are of great significance for achieving its high economic value and efficient recovery. However, selective preferential separation and extraction of rhodium have to face many difficulties, such as its kinetically inert properties, being prone to hydration and hydrolysis reactions, etc. This paper reviews various promising improvements and new technologies for selective preferential separation and extraction of rhodium from mixed metal solutions, including precipitation, liquid–liquid extraction, adsorption and other emerging technologies. The advantages and disadvantages of those reported technologies were evaluated. It is pointed out that the selective preferential adsorption of rhodium based on molecular recognition and ion imprinting is a promising rhodium recovery technology, which is economical and consistent with the concept of green chemistry. Full article

Valuation methodologies vary across industries because firms differ in capital intensity, asset life, earnings stability, and exposure to risk. This study examines the valuation approaches used by South African equity analysts across the diversified mining, platinum group metals mining, gold mining, retail, and banking sectors over the 2018–2026 period, with non-financial firm coverage extending to 2024 and banking sector coverage extending to 2026. Using qualitative document analysis of 201 equity research reports covering 24 Johannesburg Stock Exchange-listed companies, including 19 non-financial firms and the five largest South African banks, the study identifies clear clustering of valuation methods by industry. The findings show that resource-based sectors are predominantly valued using intrinsic approaches such as life-of-mine discounted cash flow (DCF) and risk-adjusted net present value (NPV), while retail firms are primarily valued using earnings-based multiples. Gold mining exhibits a hybrid valuation pattern, and banking institutions are valued using balance-sheet- and profitability-based approaches anchored on book value, return on equity, and dividend flows. Overall, the results suggest that valuation practices in the sampled equity research reports are strongly industry-specific and broadly aligned with the underlying economic characteristics of the sectors analysed. The study contributes to the limited empirical literature on professional valuation practice in African capital markets and provides insights relevant to analysts, investors, and regulators. Full article

Rhodium is a high-value strategic platinum-group metal extensively applied in automotive exhaust purification, fine chemicals, glass production and high-temperature materials. Restricted by uneven primary resource distribution and volatile market prices, recovering rhodium from secondary resources has become increasingly critical. Solvent extraction is regarded as a promising technology for continuous and selective separation of rhodium, yet direct extraction of Rh(III) from chloride media faces severe industrial limitations. These bottlenecks are mainly attributed to diversified chloro-aqua complexes, kinetic inertness of low-spin Rh(III), strong hydration capacity and polynuclear species generation, while solution aging and inconsistent thermodynamic-experimental results further complicate extraction behaviors. This review systematically summarizes recent advances in rhodium solvent extraction from chloride media, correlating aqueous speciation regulation, activation chemistry, extractant molecular structure and extraction-stripping mechanisms. Special emphasis is placed on SnCl₂-, ascorbic acid-, trichloroacetic acid- and malonate-assisted activation systems, as well as amine-, phosphorus-, sulfur-based, synergistic, ionic-liquid and deep-eutectic-solvent extractants. Key factors affecting extraction efficiency, distribution ratio, selectivity and stripping performance are clarified, and current challenges are outlined. Future research should focus on quantitative speciation analysis, in situ mechanistic characterization, targeted extractant design, and integrated evaluation of extraction, stripping, recyclability, cost and real-feed adaptability, so as to provide theoretical support for efficient and clean rhodium recovery. Full article

This study investigates the optimized recovery of platinum group metals (PGMs), particularly platinum (Pt) and palladium (Pd), together with associated base metals from UG2 ore through an integrated mineralogical–statistical approach. Comprehensive characterization using X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and inductively coupled plasma optical emission spectroscopy (ICP-OES) established ore composition, textural features, and PGM distribution, revealing Ni (0.28%), Cu (0.04%), Zn (0.04%), Pb (0.06%), and major gangue components Si (17.65%), Fe (13.33%), and Cr (7.37%). ICP-OES further quantified 1.18 g/t Pt, 1.41 g/t Pd, and 0.05 g/t Au in the run-of-mine sample. These mineralogical insights informed the design of flotation experiments using Response Surface Methodology (RSM) with a Central Composite Design (CCD), enabling systematic evaluation of dosages, pulp chemistry, and operating conditions. Optimal flotation parameters—collector dosages of 200–900 g/t, depressant dosages of 400–900 g/t, pulp pH of 8.5–9.5, and a flotation time of ~10 min—yielded recoveries ranging from 6.8% to 23.9% (Ni), 3.5% to 100% (Cu), 9.5% to 100% (Zn) and averaging 80.1% (Pb). Post-flotation ICP-OES confirmed significant enrichment of PGMs, with Pt reaching 12.00–16.50 g/t, Pd reaching 11.60–15.10 g/t, and Au reaching up to 0.47 g/t under optimal conditions. By explicitly coupling mineralogical characterization with CCD-based optimization, this work demonstrates a robust framework for enhancing UG2 flotation performance, offering practical pathways for improved economic viability, reagent efficiency, and sustainable resource utilization. Full article

Due to the constant need to develop biocompatible materials with osteoconductive and osteoinductive properties, the main objective of this study was to evaluate and characterize the carbon fiber obtained from fiber polyacrylonitrile textile carbon fiber (PAN), in the different forms: non-activated carbon fiber felt (NACFF) and activated carbon fiber felt (ACF) with silver (Ag-ACF), gold (Au-ACF), copper (Cu-ACF), palladium (Pd-ACF) and platinum (Pt-ACF), on the cell behavior and osteogenesis of mesenchymal cells. For characterization: scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and Raman analysis. In vitro analysis was performed on rat mesenchymal stem cells. For each experimental group, 5 wells (n = 5) were made where cell proliferation (CP): cell viability (CV), mineralization nodule formation (MNF), total protein content (PT) and alkaline phosphatase activity (APC) were quantified, and cell morphology was analyzed by direct fluorescence, genotoxicity and cell interaction by SEM. The data passed the normality test and was followed by the one-way ANOVA test, followed by the Tukey test, using the conventional significance level of 5%. All the samples were statistically similar in terms of cell proliferation, except for the Ag-ACF group in relation to the control group (C). For cell viability, C obtained greater viability than the other groups, while ACF obtained a statistical difference and was superior to the Ag-ACF, Cu-ACF, Pt-ACF groups, being statistically similar to the Au-ACF and Pd-ACF groups. In the evaluation of ACP, the Ag-ACF and Cu-ACF groups were lower than the C, and other groups; for the characterization tests Au-ACF and Pd-ACF showed a more homogeneous metal distribution compared to the other groups. Cu-ACF and Ag-ACF showed some toxicity and low induction of osteoblastic differentiation. Although platinum showed relative cellular viability, a high micronucleus count was reported for this ion. In conclusion, ACF has the potential to be developed as a future biomaterial with good cell viability. Carbon fibers incorporated with gold and palladium ions showed potential for future application as supports for bone repair. Full article