Search Results (154)

Metal-bearing tailings, slimes, metallurgical residues, spent catalysts, ashes, sludges, batteries, and electronic wastes are increasingly important secondary resources, but recovery is constrained by low and variable grades, fine particles, complex phase associations, passivation, and impurity-sensitive downstream processing. Hydrodynamic cavitation (HC) can modify selected flowsheet functions through interfacial renewal, localized mechanical action, gas–liquid transfer, fine-bubble generation, particle conditioning, and phase dispersion. The evidence was critically appraised across three independent dimensions: system relevance, causal attribution, and endpoint completeness. Application-level evidence is most developed for transport intensification in selected scheelite, uranium-bearing, and refractory-gold systems; particle conditioning and washing; spent-catalyst coating liberation; metal-bearing sludge treatment; copper cementation; and preparation of liquid emulsion membranes. Representative secondary-feed studies report conditioning, preconcentration, mobilization, and downstream separation responses, but complete feed-to-product recovery with controlled liquid and solid loops remains uncommon. Evidence is especially limited for battery black mass, electronic wastes, rare-earth-bearing residues, complex slags, metallurgical dusts, and multi-metal streams. HC is therefore most credible as a targeted module applied to a verified process limitation. A flowsheet advantage is established only when local gains persist through product recovery without offsetting increases in chemical use, water demand, energy consumption, equipment wear, or residual-stream burden. Full article

Ion-imprinted polymers (IIPs) are advanced adsorbents featuring selective recognition cavities for targeted metal ion capture, offering a promising route to high-efficiency separation in extractive metallurgy. In the present work, the evolution, design principles, synthesis strategies, separation mechanisms, and practical applicability of IIPs for metal recovery from complex aqueous matrices are overviewed. Key material components, including functional monomers, crosslinkers, template ions, initiators, solvents, and support materials, are discussed in relation to adsorption capacity, selectivity, kinetics, stability, and recyclability. Major preparation routes, such as surface imprinting, bulk polymerization, in situ polymerization, and sol–gel methods, are critically compared to clarify their advantages and limitations. Recent applications for base metals, precious metals, and rare-earth elements demonstrate that IIPs can achieve high specificity and rapid equilibrium under optimized conditions. However, their translation from simulated solutions to real leachates remains constrained by interfering ions, organic contaminants, mass transfer resistance, incomplete template removal, and matrix complexity. Mitigation strategies, including sample pretreatment, improved polymer architecture, and hybrid supports, are therefore emphasized. Additionally, chemometric modelling, machine learning, or artificial intelligence-assisted design may be implemented to advance the prospects of IIPs in industry. Conclusively, IIPs represent a strong separation platform, yet industrial deployment requires robust validation with real feed streams and scalable regeneration protocols during column operation, as well as under chemically aggressive conditions at scale. Full article

Hospital wastewater has begun to act as an important source of emerging contaminants, including rare earth elements (REEs), mostly lanthanides, and radiopharmaceutical residues originating from diagnostic and therapeutic nuclear medicine procedures. The increasing use of gadolinium-based contrast agents, lutetium-containing therapeutics, technetium-99m tracers, iodine-131, yttrium-90, and gallium-68 radiopharmaceuticals has raised growing concerns regarding the release of radioactive and metal-containing compounds into aquatic environments. Conventional wastewater treatment plants are often inefficient in removing these contaminants because of their high chemical stability, low environmental concentrations, and complex aqueous speciation. In this context, hybrid nanomaterials containing silver nanoparticles (AgNPs) have attracted increasing interest for both monitoring and remediation applications. AgNP-based systems exhibit unique plasmonic, catalytic, antimicrobial, and sensing properties that can be exploited in adsorption, photocatalysis, membrane filtration, electrochemical detection, and surface-enhanced Raman spectroscopy (SERS). This review critically analyzes recent advances in hospital wastewater treatment and how hybrid nanomaterials containing silver nanoparticles (AgNPs) are emerging. The review places a particular focus on contamination by REEs and radiopharmaceuticals residues, which to date, as far as we know, remains a challenging and understudied aspect, as reflected by limited publications. Full article

The growing demand for rare earth elements (REEs), heavy metals (HMs) and precious metals (PMs) has intensified interest in sustainable recovery strategies from secondary resources, including mining residues, industrial effluents and waste electrical and electronic equipment (WEEE). These streams represent exposure interfaces, because soluble and bioavailable metal species may persist, bioaccumulate and contribute to oxidative stress, genotoxicity, carcinogenic outcomes and chronic systemic effects. This systematic review, conducted following PRISMA guidelines, evaluates the thermoacidophilic red microalga Galdieria spp. as an extremophilic platform for metal bioremediation, recovery and upstream risk reduction. Galdieria spp. combines tolerance to low pH, elevated temperature and high metal loads with rapid surface biosorption and, in living biomass, slower intracellular sequestration and detoxification. Its interaction with REEs, PMs and toxic HMs is mediated by cell-wall functional groups, extracellular polymeric substances, redox-active processes and metabolic flexibility shaped partly by horizontal gene transfer (HGT). The review discusses matrix complexity and adsorption–desorption cycles, highlighting their implications for real industrial streams. Overall, Galdieria spp. emerges as a robust extremophilic bio-interface for selective metal recovery, hazardous waste mitigation, circular-economy biorefinery models and prevention of metal-associated risks to environmental and human health, while current scale-up limitations and process-oriented research priorities are identified. Full article

This study characterizes the physicochemical properties of coal gangue in Huainan, a typical coal resource-based city in China, and evaluates variations in its chemical composition and associated ecological risks. The results show that the coal gangue in the Huainan mining area is composed mainly of quartz and clay minerals, with SiO₂ and Al₂O₃ together accounting for over 86% of the total composition. Rare earth element concentrations are generally higher than background levels, whereas heavy metal concentrations are generally below the risk screening values for soil contamination of agricultural land. Complex associations are observed among the elements in coal gangue. The correlation coefficients between SiO₂ and the other oxides or heavy metals range from −0.750 to −0.993, indicating significant negative correlations and suggesting that the silicate mineral phase occurs independently of other element-enriched phases. The potential ecological risk index (RI) for heavy metals ranges from 33.75 to 300.71 and is driven primarily by Hg and Cd. The RI for rare earth elements ranges from 98.9 to 220.3, with Lu as the key influencing element. The predicted probability of adverse biological effects is 14–15%. Overall, classified management of coal gangue in the Huainan mining area is recommended, together with strengthened continuous monitoring of Hg and Cd and optimization of ecological disposal strategies by integrating potential ecological risk assessment with analysis of adverse biological effects, thereby further supporting the green transition of resource-depleted cities. Full article

Fresh flotation tailings represent an underutilized archive of mineralogical and geochemical information in which multiple strands of evidence for ore-forming processes and post-depositional modification can be preserved. Detailed characterization of tailings is also vital for assessment of their future potential as a secondary source of recoverable by-products. This study investigates residual mineral speciation and mineral distributions in size fractions of tailings from the Prominent Hill iron oxide–copper–gold (IOCG) deposit, South Australia, with emphasis on rare earth element (REE) minerals and associated phases containing uranium (U). Assemblages of REE minerals can be highly complex at the micron scale and include sequences of mineral replacement, notably monazite → florencite, and monazite → synchysite. Bastnäsite-(Ce) commonly appears paragenetically early and is frequently altered or replaced by synchysite and parisite, supporting episodes of REE remobilization and reconcentration over geological time. Uranium is closely associated with REEs, and U-mineral assemblages are similarly characterized by intricate replacement relationships between uraninite and secondary phases. Uraninite is variably replaced by coffinite and the U-carbonate wyartite, reflecting changes in redox state, silica activity, and fluid composition. Additional replacement pathways from uraninite to Cu–Fe sulphides, including bornite and chalcopyrite, are documented and indicate coupled dissolution–reprecipitation of sulphides and U-minerals during superimposed hydrothermal activity. Preservation of mineralogical relationships within tailings drawn from multiple parts of a large deposit highlights their value as an essentially untapped library of information to reconstruct deposit evolution, complementing traditional study of selected drill core samples. Systematic investigation of tailings from large deposits can improve genetic models for large copper deposits, including but not restricted to IOCGs, and provide essential insights into REE behaviour, uranium remobilization, and critical metal potential. These findings emphasize the scientific and economic value of tailings-based studies for improved resource characterization, refining metallogenic interpretations, guiding future exploration strategies, and assessing opportunities for reprocessing and metal recovery in large ore systems worldwide across diverse geological settings. Full article

The increasing demand for lithium (Li), cobalt (Co), and rare earth elements (REEs) driven by battery technologies, electrification and renewable energy systems has intensified the interest in recovery pathways as an alternative to conventional mining. High-salinity mine waters—including lithium brines, geothermal fluids, and metallurgical effluents—represent both an environmental liability and a significant secondary resource for metal recovery. However, extreme ionic strength, complex metal speciation, and strong competition from major ions severely limit the efficiency and selectivity of traditional extraction technologies. Microalgae and cyanobacteria are promising biological agents for metal recovery via biosorption, bioaccumulation, and extracellular polymeric substance (EPS)-mediated binding, especially in saline and hypersaline systems. This review synthesises current knowledge on microalgal-based recovery of Li, Co, and REEs from high-salinity waters, emphasising co-design principles that integrate strain physiology, their adaptation to the extreme operating conditions, water chemistry, and process engineering. Halotolerant and extremophilic taxa—Nannochloropsis oceanica, Galdieria sulphuraria, and Synechococcus elongatus—are examined as representative models for complementary metal-binding mechanisms and operational niches. Limitations such as weak affinity for lithium, competitive ion suppression, desorption inefficiencies, and scale-up challenges are discussed. Emerging strategies such as modular multi-strain systems, hybrid bio-physicochemical platforms, and biomass valorisation are also addressed. The review concludes that microalgal systems, when co-designed for selectivity and resilience, can contribute to the strategic recovery of critical materials that align with EU, UK and US policies. Full article

The sustainable recovery of rare earth elements (REE-Y) from electronic waste is critical for clean-energy technologies. Yet, the commercial viability of recovering REE-Y from shredder residue char (SR-char) remains underexplored. Because recovery processes are heavily influenced by operational costs, evaluating economic feasibility alongside metallurgical performance is essential. This study assesses a hybrid physical–chemical process using SR-char, integrating particle size classification and dry magnetic separation with optimized hydrochloric acid leaching. A first-order gross-profit screening model was also developed to evaluate the direct reagent economics of the proposed process. This framework calculates Revenue minus Acid and Neutralization Costs only, excluding capital expenditures (CapEx), labor, utilities, downstream separation losses, and the cost of the magnetic separation step. Results show that magnetic separation at 8000 G pre-concentrated REE-Y to >1800 g/t, and subsequent 10 M HCl leaching (60 °C, 3 h) yielded extractions of ~2000 g/t in the 500–1000 µm fraction. However, the profit model showed that maximizing extraction in the presence of high concentrations of other metals, such as Fe, Ca, and Al, results in net financial losses due to excessive reagent and neutralization costs. We conclude that physical pre-concentration to reduce non-target metal content is a critical commercial prerequisite. This targeted approach reframes the optimization criterion from metallurgical yield maximization to economic feasibility, providing a transferable screening framework for evaluating other complex secondary REE-Y resources where impurity-driven reagent consumption dominates process economics. Full article

Lignin is one of the most abundant biopolymers in nature. The major challenge in lignin depolymerization lies in the formation of complex mixtures that require extensive downstream separation. Selective depolymerization strategies aim to overcome this limitation by promoting controlled bond cleavage while suppressing undesired secondary reactions. In this work, a series of rare-earth-free, perovskite-type mixed metal oxides with general compositions Zn_xNi_1–xTiO₃ and Cu_yNi_1–yTiO₃ were synthesized and evaluated as heterogeneous catalysts for the base-catalyzed depolymerization of lignin. Among the investigated materials, CuTiO₃ exhibited superior catalytic performance, enabling the formation of vanillin as the dominant monomer with high selectivity. The selected catalyst was further characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer–Emmett–Teller (BET) surface area analysis. The combined effects of key reaction parameters, including temperature, pressure, lignin-to-catalyst ratio, NaOH concentration, and reaction time, were systematically investigated using response surface methodology (RSM). Under the optimized conditions (154 °C, 0.3 MPa, lignin-to-catalyst ratio of 24.5:1, 10 mL of 0.5 M NaOH, and 12 h reaction time), a monomer yield of 11.5 ± 0.46% with ~81% GC-selectivity toward vanillin was achieved. These findings demonstrate that perovskite-type titanates can serve as robust and reusable catalysts. Full article

The subject of this study is the electrochemical synthesis of samarium–cobalt (Sm-Co) alloy coatings on a copper substrate from aqueous solutions using chronoamperometric methods. The study focused on assessing the effect of ecological complexing agents—L-arginine and glycine—on the deposition kinetics and quality of the deposits obtained within a potential range of −1.1 V to −1.8 V vs. Ag/AgCl. Morphological analyses indicated that the type of amino acid used determines the layer growth mechanism. It was found that exceeding the potential of −1.4 V results in a rapid increase in samarium content in the alloy, reaching maximum values of 29 at.% for the system with L-arginine and 35 at.% for the system with glycine at a potential of −1.8 V. X-ray Diffraction (XRD) structural studies confirmed the successful synthesis of the Co_8.5Sm intermetallic phase directly by electrodeposition, while X-ray Photoelectron Spectroscopy (XPS) analyses indicated the presence of oxides and hydroxides on the deposit surface. Despite obtaining a high samarium content, it was observed that intense hydrogen co-evolution at low potential leads to a decrease in current efficiency and the formation of internal stresses and cracks in the structure of the coatings. Full article

The Judd–Ofelt (J–O) intensity parameters and oscillator strengths are key to understanding the optical transition properties of rare-earth-doped glasses. However, the scarcity of experimental samples and the complex nonlinear relationship between composition and spectral properties pose significant challenges to accurate predictions. To address this, we propose a generalizable framework that integrates conditional generative adversarial network (cGAN)-based data augmentation with an attention-embedded artificial neural network (ANN)–support vector regression (SVR) hybrid model. The cGAN generates physically plausible virtual samples to enrich data distribution and enhance generalization in sparse compositional regions. The attention mechanism in the ANN identifies critical compositional features, which are then leveraged by SVR for robust regression of parameter trends. The framework demonstrates high predictive accuracy for Er³⁺-doped glasses, achieving R² values above 0.93 for Ω₂, Ω₄, and Ω₆, and exhibits strong generalization performance on independent Dy³⁺- and Nd³⁺-doped datasets without task-specific retraining, confirming its practical applicability across multiple rare-earth ions. The model maintains consistency across diverse glass host systems (tellurite, borate, phosphate, silicate/germanate, heavy-metal oxide), and the attention analysis reveals feature importance aligned with established glass chemistry principles. Demonstrated on Er³⁺, Dy³⁺, and Nd³⁺, with potential for a broader range of rare-earth ions through transfer learning and future dataset extensions, this approach offers a data-driven, physics-informed tool for the targeted design of rare-earth optical materials in next-generation optical sensors. Full article

The printed circuit board (PCB), a central component of most electronic devices, represents a significant fraction of the electronic product waste stream. The complex composition of PCBs, consisting of metals, polymers, and fiberglass, requires specialized recovery steps to reclaim valuable and critical materials and the safe disposal of brominated compounds. In this review paper, we describe the current state of critical material recovery and traditional recycling technologies and identify key obstacles to large-scale implementation. Metals present at high concentrations, such as copper, lead, and iron, are conventionally recovered from PCBs using hydrometallurgical, pyrometallurgical, or electrometallurgical processes. Hydrometallurgical methods achieve high selectivity through chemical leaching but pose significant challenges for effluent and reagent recovery. Pyrometallurgical methods facilitate rapid metal separation through smelting but require substantial energy and may release harmful gases. Electrometallurgical techniques produce high-purity metals but are constrained by pretreatment requirements and the consumption of energy. The non-metallic fraction of PCB waste is recycled using thermochemical conversion, microwave-aided heating, and direct recycling of epoxy–fiberglass composites, enabling material or energy recovery. The recovered polymer from direct recycling may have reduced mechanical strength and poor compatibility with new polymer matrices, and the resulting products from the thermal conversion suffer from incomplete conversion, degradation of quality, and residual contamination, as compared to synthetic polymers. Recent process developments have focused on extracting rare earth and supply-critical materials present at lower concentrations in the waste stream. The literature on existing and emerging approaches for recycling PCB wastes is reviewed to identify sustainable, economically viable, and environmentally responsible strategies for the recovery and reuse of critical materials from waste streams. Full article

Vegetation strongly influences soil formation, yet its effect on Rare Earth Element (REE) distribution and fractionation across treeline ecotones remains insufficiently constrained. The present study investigated how contrasting plant communities, Vaccinium myrtillus heathlands and Picea abies forests, affect pedogenetic pathways and REE behavior in sandstone-derived soils of the Northern Apennines (Italy). Six soil profiles were characterized for bulk geochemistry, selective Fe–Al extractions, particle-size distribution, and REE concentrations. Principal component analysis and hierarchical clustering identified pedogenetic drivers and horizon groupings. Under Vaccinium myrtillus, thick acidic organic horizons promoted organo-metal complexation and incipient podzolization, whereas Picea abies soils showed thinner organic layers and enhanced mineral weathering, leading to Bw development with higher silt–clay contents and elevated Al/N ratios. These pathways were captured by Fe–Al indicators and the Spodic Index. REE distributions showed vegetation-related differences in surface horizons and Eu–Ce anomalies, but they did not reproduce Fe–Al pedogenetic clusters, reflecting strong parent-material control. The coexistence of podzolic and cambic pathways at the treeline highlights pronounced spatial heterogeneity and vegetation effects. Plant composition may redirect pedogenesis, influencing nutrient cycling and metal mobility. Additionally, these findings emphasize the need to integrate multivariate statistics with established pedogenetic indicators when evaluating geochemical properties in mountain soils. Full article

Rare-earth elements (REEs), which include the entire lanthanide series together with scandium and yttrium, have unique electronic configurations and coordination chemical properties that provide them with special magnetic, optical, and redox abilities. Generally used for diagnostic imaging and theranostic applications, increasing evidence emphasizes their potential as direct anticancer agents. This review aims to present a thorough investigation of the studies published in the last ten years that focus on the intrinsic anticancer properties of REE-based molecular complexes and nanostructures, without discussing their recognized imaging functions. Rare-earth compounds exhibit selective cytotoxicity against malignant cells via mechanisms that mainly include modulations in the generation of reactive oxygen species, mitochondrial dysfunctions, interaction with DNA molecules, apoptosis, and ferroptosis induction, as well as radiosensitization. Molecular complexes that are based on the trivalent coordination chemistry of REEs enable them to target biomolecules like DNA and serum albumin. Nanostructured systems, on the other hand, render tumors more responsive to treatment by improving the cellular uptake, enabling surface functionalization, and controlling ROS generation. Terbium, thulium, yttrium, scandium, ytterbium, cerium, erbium, dysprosium, and europium show different levels of anticancer activity in both in vitro and in vivo cancer models. They often exert more toxicity in tumor cells than in normal tissues, thus exhibiting selective anticancer effects. The findings collectively underscore the therapeutic potential of REE-based compounds as novel metal-based anticancer agents and advocate for additional mechanistic and translational research to enhance their clinical applicability. Full article

The southeastern Iberian Peninsula, particularly the Águilas Arc within the Neogene Volcanic Province (NVP), represents a promising geothermal domain with complex tectonics and geology. The Palomares Fault Zone (PFZ), a key shear structure initiated during the Late Miocene, acts as a conduit for fluid migration, promoting mineralization and potential anomalies of rare and critical metals through fluid–rock interaction. This study investigates such interactions in the southernmost Águilas Arc, focusing on the El Arteal fault segment within the eastern PFZ strand. Mineralogical, geochemical, and hydrogeological analyses were performed using XRD, SEM, and ICP-MS techniques. Results reveal six mineral assemblages (MA) within the fault segment where the fault gouge samples were characterized by cataclastic textures and the occurrence of authigenic minerals, including halite, kaolinite, illite, paragonite, goethite, hematite, gypsum, barite, celestine, and quartz. Geochemical data indicate enrichment signatures in large-ion lithophile elements (LILE) and minor chalcophile and light rare-earth elements (LREE). Two thermal hydrofacies with alkaline metals enrichment were identified in wells and mine shafts: (1) Na⁺SO₄²⁻ and (2) Na⁺Cl⁻, where the latter exhibits high Na⁺ and Cl⁻ concentrations toward deeper sectors. These findings suggest multiple stages of fluid–rock interaction controlled by temperature: an early phase dominated by epithermal mineralization, followed by late-stage circulation of hypersaline fluids. This evolution provides an abnormal geochemical signature that is unique in the Aguilas Arc Geothermal System. Full article