Search Results (4,123)

Mining and metallurgical residues represent one of the largest untapped secondary raw-material resources in Europe; however, their critical raw material (CRM) potential remains insufficiently quantified. This study applies a comprehensive mineralogical, geochemical, and geostatistical framework to evaluate nine distinct waste types from the Cartagena–La Unión Mining District (SE Spain), a historically exploited polymetallic system. A total of 79 samples were analysed using X-ray diffraction, wavelength-dispersive X-ray fluorescence, and advanced multivariate statistical techniques (correlation analysis, principal component analysis and hierarchical clustering) to identify geochemical associations controlling CRM distribution. The results reveal strong geochemical heterogeneity, with systematic enrichment in Co, Ni, Cu, Ga, Nb, and rare-earth proxies. Three dominant geochemical controls were identified: (i) a lithogenic silicate association governing Al–Si–Ti–Nb patterns, (ii) a sulphide-derived metalliferous association characterized by Cu–As–Sb, and (iii) an oxidation–adsorption association responsible for Ga–Y affinity. Several CRM concentrations approach or exceed typical global ore grades for secondary resources, particularly in flotation-derived and oxidation-rich residues. Geostatistical modelling confirms spatially coherent CRM hotspots, with base-metal enrichment linked to sulphide relics and Ga–Nb–Y controlled by Fe–Mn oxyhydroxides. Environmental assessment indicates potential metal mobility under acidic conditions, while also highlighting significant remediation benefits associated with residue reprocessing. Taken together, this study provides a robust and reproducible methodology for CRM assessment in legacy mining wastes and identifies priority residue types within the district with the highest strategic recovery potential. Full article

Electrocatalytic nitrate reduction to ammonia (NH₃) offers a sustainable alternative to the Haber–Bosch process while enabling remediation of nitrate-contaminated water. However, the mechanistic origin of performance differences among bimetallic catalysts remains poorly understood, particularly regarding the metal-dependent evolution of reaction intermediates. Here, we construct a series of phase-pure tandem Cu–M catalysts (M = Co, Ni, Fe, Sn) by physically integrating commercial nanoparticles to examine the role of the secondary metal. In this architecture, Cu governs nitrate adsorption and its initial reduction to nitrite, whereas M dictates downstream hydrogenation toward NH₃. Operando ATR–FTIR spectroscopy reveals that NH₃ FE is determined by the hydrogenation kinetics of nitrite-derived intermediates rather than nitrate activation itself. Among the examined systems, Cu–Co achieves optimal kinetic matching, enabling rapid nitrite consumption and continuous hydrogenation, delivering an ammonia Faradaic efficiency of 91.2% with minimal nitrite accumulation (~1.0%) and a yield rate of 0.86 mmol h⁻¹ cm⁻² at −0.5 V vs. RHE. In contrast, Ni and Fe exhibit sluggish hydrogenation, while Sn induces pronounced intermediate buildup. These findings identify nitrite hydrogenation as the selectivity-determining step in tandem nitrate reduction and establish the chemical nature of the secondary metal as a decisive descriptor for rational catalyst design. Full article

To address the critical challenges of sluggish C-C coupling kinetics and the propensity for over hydrogenation to ethane (C₂H₆) in the photocatalytic CO₂ reduction to ethylene (C₂H₄), this study designed a synergistic bimetallic Pt/Co cluster catalyst supported on a covalent organic framework (COF), designated as PtCo-TpBD COF. This catalyst is designed to modulate the adsorption of key intermediates via Co clusters to suppress over-hydrogenation, while leveraging Pt clusters to promote C-C coupling, thereby achieving highly selective C₂H₄ production. Through a series of structural characterization analyses, it was confirmed that Pt/Co clusters were successfully confined within the pores of the COF, and significant electronic interactions were observed. In situ infrared spectroscopy revealed that the introduction of Co clusters effectively weakens the adsorption strength of the CO* intermediate, while the incorporation of Pt clusters promotes C-C coupling. In visible-light-driven gas-phase CO₂ reduction, this catalyst delivered exceptional activity, reaching an C₂H₄ formation rate of 7.54 μmol g⁻¹ h⁻¹ and an C₂H₄ selectivity of 90.1%, along with remarkable inhibition of deep hydrogenation byproducts including C₂H₆. This study not only provides a successful example for constructing efficient bifunctional photocatalysts to achieve highly selective conversion of CO₂ to C₂H₄, but also highlights the great potential of COFs as advanced platforms for integrating multifunctional metal clusters and precisely tuning catalytic selectivity. Full article

A sustainable strategy was developed to valorize rabbit manure waste by synthesizing a porous quaternary Ni-Co-Zn-Fe layered double hydroxide/biochar nanocomposite (QL-RMB) for the efficient removal of Mn(VII) in the form of permanganate (MnO₄⁻) from aqueous solutions. The QL-RMB adsorbent exhibited a well-developed mesoporous structure with uniformly dispersed nanoparticles, achieving 73% MnO₄⁻ removal within 60 min under optimized conditions (pH 3.0; dosage 0.5 g L⁻¹). Adsorption followed pseudo-second-order kinetics and was best described by the Freundlich isotherm model (R² > 0.98), yielding a maximum Langmuir adsorption capacity (q_max) of 45.13 mg g⁻¹. Statistical physics modeling confirmed a multi-ionic, vertically oriented adsorption configuration, while thermodynamic analysis demonstrated that the process was spontaneous and exothermic, governed by electrostatic attraction, anion exchange, and surface complexation. The QL-RMB composite exhibited excellent MnO₄⁻ selectivity in the presence of competing ions (selectivity coefficients: 24.96 for Fe³⁺, 31.59 for Ni²⁺, 23.56 for Zn²⁺) and retained significant removal efficiency (73.96%) after five regeneration cycles. In a circular economy approach, the Mn (VII)-spent adsorbent (QL-RMB/Mn) was valorized as an electrocatalyst for urea electro-oxidation, achieving a current density of ~127.19 mA cm⁻² for pristine QL-RMB, which increased to ~217.07 mA cm⁻² after Mn(VII) adsorption (QL-RMB/Mn) in 1 M KOH/1 M urea. Batch scale-up studies revealed an efficiency of 42.55 g or 95% MnO₄⁻ removal from 50 L water, with a low estimated production cost of 0.0602 USD g⁻¹. Environmental sustainability was confirmed by the National Environmental Methods Index (NEMI), modified Green Analytical Procedure Index (Mo-GAPI), Eco-scale (score: 77), and Analytical GREEness (AGREE) assessment frameworks. Full article

The photocatalytic activity of TiO₂ can be increased by incorporating it into a composite with an electron-trapping co-catalyst. MXene can perform this task as an electron-conducting material. In addition to trapping electrons, it also affects the defects in TiO₂ near the interface. To screen for the best photocatalytic performance, three types of composites were prepared: by physical mixing, chemical deposition, and ALD. During characterization, the structural, optical, and photoelectrochemical properties were determined. Photocatalytic activity was examined in suspension (phenol conversion) and on a layer (gas phase ethanol conversion). It was found that the composite containing the lowest proportion of cocatalyst (1 wt.%) had the highest photocatalytic activity. According to the results of photocatalytic activity measured in suspension, the physical mixtures were proven to be more effective than neat TiO₂, with the composites converting approximately the total amount of phenol in ~40 min, while TiO₂ required ~80–90 min to do so under the same conditions. Thus, the electron-trapping role of MXene is clearly demonstrated in suspension applications, which is also confirmed by other characterization methods (photoluminescence, photocurrent density). TiO₂ performed best during ethanol conversion, as it has the highest ethanol adsorption capacity (33.41%). During ethanol conversion tests, the MXene electron-trapping property was most effectively demonstrated in composites formed using the ALD method. Full article

Copper slag was used as a raw material to prepare lithium ferrite by the solid-state reaction method at different Li:Fe molar ratios. The obtained materials were characterized by XRD, SEM, and N₂ adsorption–desorption, and their CO₂ capture behavior was evaluated using thermogravimetric and temperature-programmed techniques. A 7:1 Li:Fe molar ratio allowed to obtain Li₅FeO₄, as well as Li₄SiO₄, due to the high silicon content in the slag. CO₂ sorption tests showed that, as temperature increases, CO₂ capture increases up to 675 °C. Slag-ferrite achieved a maximum CO₂ capture of 20 wt% at 675 °C (P_CO2 = 0.2), equivalent to 62.5% of the CO₂ sorption of reagent-grade ferrite (32 wt%). Kinetic analysis of CO₂ capture using the Avrami–Erofeev model indicated that bulk diffusion is the rate-controlling step. These results provide quantitative evidence on the use of copper slag in the preparation of lithium ferrites, with potential application in a high-temperature CO₂ capture process. Full article

Recycling spent lithium-ion batteries (LIBs) is critical for resource sustainability and carbon neutrality. This work presents a green strategy in which NaA zeolite is used to preferentially recover lithium from leachate of spent NCM111 batteries, combined with temperature-regulated stepwise separation of transition metals. Benefiting from the distinct hydrated ionic radii and charge density between Li⁺ and divalent metal ions, NaA zeolite selectively adsorbs Ni²⁺, Co²⁺ and Mn²⁺, leaving Li⁺ in the raffinate. Under optimized conditions, two-stage adsorption achieves 95.6%, 96.7% and 99.7% removal of Ni²⁺, Co²⁺ and Mn²⁺, respectively, with 11% Li⁺ co-adsorption. Thermodynamic analysis reveals that the adsorption process is endothermic and thermodynamically spontaneous. The interaction strength between metal ions and NaA zeolite follows the order Ni²⁺ > Co²⁺ > Mn²⁺, and ion exchange is identified as the dominant mechanism. It is determined that 96.8% of Mn²⁺ can be recovered at 0 °C, followed by the desorption of 93.5% of Co²⁺ at 90 °C, and the sequential separation of Mn, Co and Ni is realized. Three consecutive adsorption–desorption cycles demonstrate the acceptable reusability of the Ni-loaded NaA adsorbent. High-purity Li₂CO₃ (purity 96.7%, yield 93.5%), MnO₂ (purity 99.3%, yield 98.4%) and Co₃O₄ (purity 98.8%, yield 97.6%) are obtained from the corresponding solutions. This approach provides a scalable closed-loop pathway for full-component recovery of valuable metals from spent LIBs. Full article

Formic acid (FA) has emerged as a promising liquid hydrogen storage material, yet efficient photothermal dehydrogenation catalysts with high activity and H₂ selectivity remain challenging. Herein, a polymetallic synergistic PdCu/M-ZNC (where M represents the co-doped In, Sn and Mo species) is fabricated by molten-salt-assisted pyrolysis of ZIF-8 precursors followed by metal incorporation. The unique molten salt environment effectively preserves the porous architecture of ZIF-8, enabling the secure anchoring of PdCu alloy nanoparticles onto the carbonaceous matrix enriched with M-Nₓ coordination sites. Under light irradiation, the PdCu alloy sites kinetically accelerated the overall adsorption and activation of FA molecules. Based on empirical observations and corroborated by the established literature, this alloying effect was inferred to facilitate the C-H bond cleavage and HCOO* desorption processes. Concurrently, the M-Nₓ sites act as efficient electron transfer channels, facilitating the rapid coupling of photogenerated electrons with protons (H⁺) to evolve H₂. Consequently, the optimal catalyst exhibits an enhancement in gaseous product yield (404.46 mmol/g/h) and H₂ selectivity (67.49%) at 75 °C. This work offers a catalyst design that aligns with several principles of green chemistry: it maximizes the atom utilization of precious Pd, incorporates synergistic non-precious metals within MOF-derived frameworks to enhance stability, and leverages solar energy to drive hydrogen production under mild conditions, presenting a more sustainable pathway for hydrogen release from liquid carriers. Full article

The co-pyrolysis of Chlorella vulgaris (CV) and Eucalyptus branches (EP) offers a promising strategy to enhance bio-oil yield, improve resource utilization efficiency, and alleviate environmental pressures. In this study, the microwave-assisted co-pyrolysis of CV and EP at a mass ratio of 2:1 was investigated, focusing on the catalytic performance of Ni-X (X = Mg, Cu, Fe) bimetallic modified HZSM-5 zeolites. The effects of these catalysts on pyrolysis characteristics, product distribution, and bio-oil composition were systematically evaluated. Experimental results showed that the 15% Ni-Cu/HZSM-5 catalyst exhibited the best catalytic performance, achieving the highest bio-oil yield of 16.83%; it also elevated the R_m to 0.0687 wt.%/s and reduced T_s to 2084 s. Composition analysis revealed that Ni-Cu/HZSM-5 significantly promoted the formation of hydrocarbons, increasing their relative content from 11.59% (C2E1 Group) to 28.92%, while effectively suppressing the formation of nitrogen-containing compounds, reducing their content by 5.05%. Based on these results, a possible reaction pathway is proposed in which the Ni-Cu/HZSM-5 catalyst may enhance heteroatom removal through hydrodeoxygenation (HDO) at the Ni-Cu sites, followed by cracking and aromatization at the HZSM-5 acid sites. This effect may be complemented by preferential adsorption of oxygenated intermediates over nitrogen-containing species, which could help suppress the formation of nitrogenous heterocycles. This work provides theoretical guidance for the application of bimetallic zeolite catalysts in microalgae/lignocellulose co-pyrolysis, alongside a viable pathway for valorizing Eucalyptus by-products to produce high-quality bio-oil. Full article

Metal oxide nanoparticles dispersed in water are difficult to recover because of their small size and colloidal stability. In this study, the interfacial adsorption behavior of Fe₂O₃, CoO, and CuO nanoparticles at hydrophobic ionic liquid (IL)–water interfaces was investigated and compared with that at molecular solvent–water interfaces. When CuO nanoparticle dispersions were shaken with hydrophobic ILs, bis(trifluoromethanesulfonyl)imide ([NTf₂]⁻) salts of 1-butyl-3-methylimidazolium ([BMIm]⁺) and 1-octyl-3-methylimidazolium ([OMIm]⁺), the nanoparticles were removed from the aqueous phase and accumulated at the IL–water interface, while negligible Cu was detected in the bulk IL phase. The removal efficiency decreased with increasing ionic strength below 0.05 mol/dm³ and increased with pH, indicating that electrostatic interactions between charged nanoparticles and the IL–water interface contribute to adsorption. Adsorption isotherms were empirically fitted with the Langmuir equation to estimate the maximum adsorption capacity. For negatively charged Fe₂O₃ and CuO nanoparticles, the maximum adsorption capacities at IL–water interfaces exceeded those at molecular solvent–water interfaces and the theoretical monolayer capacity estimated from nanoparticle size, suggesting multilayer adsorption or aggregation at the interfaces. These results demonstrate the potential of hydrophobic IL–water interfaces for the separation and recovery of metal oxide nanoparticles from aqueous media. Full article

This work investigates the behavior of carbon dioxide (CO₂) near the surface of different single-atom alloys to evaluate their potential as catalysts for decarbonization processes. Specifically, 26 transition metals from the first three transition series, alloyed with three low Miller index copper supports, were considered. Adsorption energies and distances of linear CO₂, trigonal CO₂, and CO* + O* on the surfaces were calculated using the semiempirical computational method MOPAC-PM7. Additionally, activation energies were determined from previously published research. The proposed methodology is less computationally demanding than DFT studies, and results show good agreement with both experimental and simulated data. This approach provides a computationally efficient methodology for screening promising materials that convert CO₂ into valuable products, such as methane and methanol. Full article

The safety of drinking water has a significant impact on human life and health, with the common presence of Pb (II) causing harm to human beings. The physical adsorption method is an effective means of removing Pb (II) from water. In this study, three types of biochar were produced through a one-step process using agricultural and forestry wastes (rape straw, bagasse, and walnut shell) as raw materials and KHCO₃ as a co-carbonization agent. The resulting biochar exhibited remarkable adsorption capacities for Pb (II). The biochar prepared via a single carbonization process demonstrates excellent adsorption performance towards Pb (II). The adsorption capacity of bagasse-derived biochar reaches 76.94 mg/g, which is 4.5-fold higher than that of the control. For walnut shell-derived biochar, the adsorption value attains 124.90 mg/g, representing a 7.5-fold enhancement. Notably, rape straw-derived biochar demonstrates the maximum adsorption capacity, up to 265.69 mg/g. Mechanistic analysis reveals that the adsorption of rape straw biochar is dominated by ion exchange, while also being influenced by physical adsorption, coprecipitation, and electrostatic attraction. Intriguingly, in this study, the sole use of KHCO₃ as a co-carbonization agent remarkably increases the specific surface area of the biochar and facilitates the formation of micropores. Without the need for pre-carbonization, this approach substantially boosts the Pb (II) adsorption capacity of the biochar. This one-step carbonization strategy exhibits distinct operational convenience and cost-effectiveness, providing promising materials for the low-cost removal of Pb (II) in natural water bodies and open environments, while also offering a viable technical route for the fabrication of high-performance biochar for heavy metal remediation. Full article

Coalbed methane (CBM) development is strongly controlled by pore structure evolution in deformed coals and its influence on hydraulic fracturing behavior. To clarify the multifractal characteristics of cross-scale pores and their control on fracturing effectiveness, this study investigated eight different deformation coals from the Ordos Basin using low-temperature CO₂/N₂ adsorption (LT-CO₂A/LT-N₂A) and high-pressure mercury intrusion porosimetry (HMIP). Micropores (<2 nm), mesopores (2–50 nm), and macropores (>50 nm) were systematically characterized, and their pore size distributions (PSDs) were quantitatively analyzed using the Coal Structure Index (CSI) and multifractal theory. The results indicate that the multifractal parameters of macropores are significantly distinct from those of mesopores and micropores, exhibiting lower H (0.824–0.893) and D₁ (0.766–0.853), and higher α₀ (1.422–1.541), ΔD (1.230–1.408), and Δα (1.459–1.642). Macropores controlled by tectonic deformation exhibit stronger heterogeneity compared to mesopores and micropores in local parts of the coal mass; PSD varies significantly with deformation rising, derived from the differential pore structure evolution during brittle–ductile transition and the multi-scale synergistic effects including maturity and composition. Combined with field fracturing curves, the results further indicate that the α₀, ΔD, and Δα of macropores are negatively correlated with breakdown pressure, with correlation coefficients of 0.51, 0.61, and 0.59, respectively, and that strong local heterogeneity of macropores favors fracture initiation and propagation and reduces breakdown pressure. Cataclastic coal is the most favorable for hydraulic fracturing, followed by undeformed coal, whereas granulated coal shows the poorest fracturing performance. Full article

While CO₂ huff-n-puff (CO₂ HnP) is a promising technique for shale oil recovery, the characteristics and controlling factors of microscopically movable oil in lacustrine argillaceous-rich shales remain poorly understood. Shale samples from the Qingshankou Formation in the Songliao Basin were collected, and a series of experiments, including low-pressure N₂ adsorption, mercury injection porosimetry, and nuclear magnetic resonance, were conducted. High-pressure and high-temperature CO₂ HnP experiments were then conducted to investigate the effects of cycle number, soaking time and changes in pore structure on movable oil distribution. The shales exhibit multi-scale pores and lamellar fractures containing substantial residual oil (41.33–52.16% saturation). CO₂ HnP effectively mobilizes oil from macropores (50–1000 nm) and fractures (>1000 nm), with a limited effect in micro–mesopores (<50 nm). Three CO₂ HnP cycles were optimal for movable oil extraction. Extending the soaking time increased movable oil by ~4%, primarily from macropores and fractures (5.59–6.05%), with minimal improvement in smaller pores. A combination of CO₂ flooding followed by CO₂ HnP increased total movable oil by 4.83–7.26%, significantly enhancing recovery from micropores (7.26%) and macropores (9.21%). This study clarifies the pore size distribution and mobilization constraints of movable oil in argillaceous-rich shales. The integrated CO₂ flooding and HnP strategy proves to be highly effective, especially for movable oil in micro–mesopores. This study is the first to investigate pore-scale movable oil in lacustrine argillaceous-rich shales during CO₂ huff-n-puff under in situ reservoir conditions, and could provide critical insights for optimizing shale oil recovery in the Songliao Basin and similar lacustrine reservoirs. Full article

Excessive phosphorus discharge from aquaculture effluent significantly contributes to coastal eutrophication, while conventional adsorbents exhibit limited phosphorus removal efficiency in high-salinity, weakly alkaline seawater effluent. This study developed iron/calcium co-modified chlorella biochar (FCBC) through co-impregnation and high-temperature pyrolysis, optimizing the preparation process via the Box–Behnken response surface method. The optimal conditions were identified as an iron concentration of 2.5 mol/L, a calcium concentration of 2.0 mol/L, a pyrolysis temperature of 717 °C, and a duration of 113 min. Under these conditions, FCBC achieved a phosphorus removal rate of 93.23% within 3 h, which was significantly higher than that of the unmodified Chlorella biochar (BC, <8% within the same reaction time). The Fe/Ca co-modification endowed FCBC with a positively charged surface, an increased average pore size of 22.773 nm, and good magnetic responsiveness (saturation magnetization of 6.68 emu·g⁻¹). FCBC demonstrated remarkable adaptability, achieving over 97% phosphorus removal across a pH range of 3 to 11, salinity levels of 5 to 40‰, and phosphorus concentrations of 1 to 15 mg/L. Its adsorption kinetics conformed to pseudo-second-order kinetics (R² = 0.987) and the Freundlich model (R² = 0.971), with efficient phosphorus removal primarily attributed to iron–calcium synergistic effects. FCBC presents significant potential for phosphorus treatment in marine aquaculture effluents. Full article