Search Results (466)

The magmatic Ni-Co-Cu mineralization in the Iken deposit in the central part of the Kun-Manie complex, Amur Oblast, Russia, hosted by an olivine-bearing websterite, is of a low-sulfide type. The fine-grained disseminations of base metal sulfides (BMS), dominantly pyrrhotite, pentlandite (a major source of Ni of industrial importance), and chalcopyrite, are followed by a scarce Pd-Pt-Ag mineralization. Elevated contents of Al in orthopyroxene (mean 2.78 wt.% Al₂O₃) along with Al–Na enrichment in clinopyroxene (diopside; mean 5.10 wt.% Al₂O₃) are associated with highly aluminous compositions of low-chromium members of the spinel–hercynite series. High levels of TiO₂ in kaersutite and titanian phlogopite also reflect a pronounced degree of fractionation of the ore-forming melt. Minor portions of sulfide melt are distributed evenly as a result of immiscibility at advanced stages of orthopyroxene crystallization, after the formation of olivine. Differentiated grains of droplet-like BMS largely settled in situ close to grain boundaries of orthopyroxene or occupied interstitial spaces of pyroxenes and olivine in association with spinel–hercynite and fluorapatite. A combination of late saturation in S with relatively quick cooling rates of the hypabyssal body prevented the effective settlement and accumulation of sulfide droplets in the ore zone. The well-developed lamellae of troilite (Fe₅₀S₅₀) exsolved from the host pyrrhotite Fe₄₈S₅₂ during subsolidus cooling, as a consequence of a low-temperature reaction triggered by a sudden drop in fO₂. An influx of mantle-derived fluid bearing CO₂, CO, and CH₄ with the rising magma could be the primary cause of the fO₂ reduction. Also, graphite-bearing metasedimentary rocks could have been assimilated. Tiny grains of minerals of noble metals (moncheite and merenskyite with essential amounts of melonite component, sperrylite, hessite, alloy Au_63.2Ag_36.8, and argentopentlandite) deposited late in a fluid-enriched medium under submagmatic conditions. Full article

Additive manufacturing has emerged as a transformative technology for fabricating complex drug-eluting medical devices, offering unprecedented design freedom and functional integration capabilities. This comprehensive review systematically analyzes 3D printing technologies applied to pharmaceutical device manufacturing, focusing on drug-eluting vascular stents as a representative application. This review covers six primary additive manufacturing techniques, ranging from high-resolution vat photopolymerization (25 μm resolution) to direct energy deposition, with a focus on their capabilities for produce pharmaceutical devices with controlled drug release properties. Novel 4D/5D/6D printing technologies introduce stimuli-responsive behaviors enabling programmable drug release profiles and adaptive device functionality. Manufacturing process optimization reveals superior design flexibility compared to conventional methods, with 85–95% reduction in design iteration time and elimination of tooling costs for complex geometries. The material landscape encompasses traditional metals (316L stainless steel, cobalt–chromium), biodegradable polymers (polylactic acid, PLA; polycaprolactone, PCL; poly(lactic-co-glycolic acid), PLGA), shape-memory materials (i.e., polymers and alloys capable of recovering a pre-programmed shape upon exposure to a specific stimulus such as body temperature, moisture, or light), and advanced nanocomposites, each offering distinct drug-loading capacities (100–500 μg/cm²) and release kinetics. Critical challenges include standardization requirements (International Organization for Standardization (ISO) 5840 and American Society for Testing and Materials (ASTM) F2606), pharmaceutical-grade manufacturing protocols, and regulatory pathways for novel drug-device combinations. This review identifies key research priorities including development of biocompatible printing materials, accelerated drug release testing protocols, and scalable manufacturing processes suitable for medical device production. This analysis demonstrates that 3D printing enables integration of multiple pharmaceutical functions within single devices, controlled spatiotemporal drug delivery, and elimination of secondary manufacturing steps for drug coating processes, advancing the development of next-generation therapeutic medical devices. Full article

The problem of chromium contamination, especially Cr(VI), in acidic wastewater has drawn significant attention, requiring effective and sustainable remediation measures. In this study, tannic-acid/Fe₃O₄-modified corn straw biochar (Fe-TA-CSB) is prepared by a grinding-calcination method to remove Cr(VI). The factors influencing the removal effect of Fe-TA-CSB are investigated through static adsorption experiments. The removal mechanism is explored by combining adsorption kinetics, isothermal adsorption, and thermodynamics, as well as characterization methods. The results show that the removal efficiency of Cr(VI) increases with the increase in pH, contact time (t), and solid–liquid ratio (m/v), but decreases with the increase in initial concentration (C₀). Under optimal conditions of TA/Fe₃O₄ mass ratio = 12.5%, pH = 3.0, m/v = 1.0 g/L, and C₀ = 10 mg/L, the removal efficiency value is 94.02%, which is approximately 81.44% after four adsorption–desorption cycles. The adsorption behavior is fitted well by the Sips isotherm model and Elovich kinetics model, suggesting the adsorption process of heterogeneous monolayer chemisorption. The removal mechanism of Cr(VI) by Fe-TA-CSB involves electrostatic interaction with Cr(VI), reduction in Cr(VI) to Cr(III) through C–O and Fe(II), and complexation of reduced Cr(III) with the introduced Fe–O and phenolic hydroxyl groups. Fe-TA-CSB is an environmentally friendly and renewable adsorbent with good potential for the treatment of acidic wastewater. Full article

Groundwater contamination by redox-sensitive elements (RSEs) such as arsenic (As), chromium (Cr), vanadium (V), and selenium (Se) pose a critical challenge in alluvial aquifers, where seasonal hydrological forcing drives dynamic hydrogeochemical and redox conditions. This study investigates the seasonal evolution of groundwater hydrogeochemistry and multi-metal behavior in shallow aquifers of the Mid-Gangetic Plain, India, with particular emphasis on the role of seasonal redox decoupling. Monsoon conditions were dominated by strongly reducing environments (ORP: −150 to −70 mV), predominantly Ca–Mg–SO₄ and Na–Cl type facies. Under these conditions, significant correlations among RSEs in particular (As–V, As–Se) indicated coupled mobilization governed by the reductive dissolution of Fe–Mn (oxyhydr)oxides. Monsoon groundwater also exhibited strong associations between RSEs and agronomic indicators (NO₃⁻, SO₄²⁻), suggesting the influence of recharge-mediated agricultural inputs on redox-sensitive geochemical processes. In contrast, post-monsoon conditions showed a clear transition to sub-oxic states (ORP up to +121 mV) and were dominated by Ca–Mg–HCO₃ facies, accompanied by substantial increases in bicarbonate (~372%), electrical conductivity (~62%), and total dissolved solids (~21%). Despite the partial oxidation of the aquifer system, redox-sensitive metals did not respond uniformly. Instead, inter-element correlations weakened or disappeared, indicating a transition from coupled to decoupled contaminant behavior. Arsenic concentrations increased up to 20.8 µgL⁻¹, whereas Cr and V displayed variable enrichment controlled by alkali-induced desorption and carbonate-mediated surface interactions. This transition reflects seasonal redox decoupling, whereby seasonal redox shifts lead to metal-specific rather than coordinated multi-metal behavior. We propose a Seasonal Redox Decoupling Framework (SRDF) to explain the shift from coupled reductive release during monsoon conditions to selective mobilization pathways in the post-monsoon period. These findings demonstrate that seasonal redox shifts control not only metal concentrations but also inter-element relationships, leading to metal-specific risk profiles. This underscores the need for seasonally adaptive monitoring and management strategies in hydrologically dynamic alluvial aquifers. Full article

Heavy metals such as copper and zinc serve as essential trace elements for photosynthetic organisms at appropriate concentrations. However, at elevated levels, these metals (along with non-essential metals like chromium, lead, mercury, and cadmium) exert severe toxic effects on aquatic life. Heavy metal toxicity primarily relates to oxidative damage in living systems through a direct increase in reactive oxygen species (ROS) and reduction in cellular antioxidant capacity. Previous research on algae of different types with different coverings led us to complete the comparative framework. For this purpose and to assess biotechnological potential, we investigated chromium effects on Euglena gracilis, which possesses a unique pellicle covering, to determine whether it could serve as a chromium biosensor or bioremediation agent. Using Raman spectroscopy and absorption microspectrophotometry (MSP), we found that chromium concentrations of up to 500 μM had no effect on Euglena chlorophyll or carotenoid profiles, consistent with the pellicle preventing chromium entry and protecting the photosynthetic apparatus. However, concentrations > 10 μM severely inhibited growth through extracellular interference with essential nutrient utilization (ammonium phosphate and vitamin B₁₂). Growth inhibition was reversible upon transfer to fresh medium, confirming that cellular machinery remained intact. These results suggest that E. gracilis cannot serve as a chromium biosensor (photosynthetic apparatus unaffected) or bioremediation agent (no chromium internalization), but its ability to maintain photosynthetic functionality in chromium-contaminated environments suggests the potential for alternative applications in polluted water biomass production. Full article

This study investigates the oxidation behavior and microstructural evolution of Sanicro 25 steel (X7NiCrWCuCoNb25-23-3-3-2) after long-term exposure to water vapor at 700 °C for 30,000 h. Particular attention was paid to the relationship between protective oxide-scale formation, chromium depletion in the near-surface region, and the possible changes in secondary-phase stability in the steel substrate. FIB-SEM tomography was applied to characterize the oxide scale and the underlying affected zone, enabling three-dimensional visualization of oxide morphology, interfacial voids, and microstructural reconstruction beneath the scale. Long-term exposure resulted in the formation of a continuous Cr-rich oxide scale with a thickness of approximately 2.6 µm and local Mn enrichment. The scale exhibited a complex multilayered morphology, consisting of outer Cr-rich oxide crystallites, fine-grained chromium oxides, and an inner heterogeneous Mn-enriched region, suggesting the possible formation of mixed spinel-type oxides. Si-enriched regions were observed near the oxide/metal interface; however, no continuous Si oxide layer was detected. Despite the presence of interfacial voids, no scale spallation was observed in the investigated regions. SEM-EDX analysis revealed a chromium-depleted subsurface zone extending to approximately 6.5 µm below the oxide scale. CALPHAD calculations suggest that local chromium depletion may reduce the thermodynamic stability of Cr-rich M₂₃C₆ carbides and the Nb–Cr–N-type Z phase. This possible reduction in phase stability may contribute to the formation of a precipitate-depleted region and local microstructural reconstruction beneath the oxide scale. In the bulk region, where oxidation effects were negligible, the microstructure consisted of an austenitic matrix containing M₂₃C₆ carbides, σ phase, Cr–Ni–Fe nitride with an A13-type structure, ε-Cu precipitates, Z phase, and W-rich Cu-containing TCP precipitates. The simulations further suggest that most secondary phases form during the early stage of annealing, whereas prolonged exposure is dominated by diffusion-controlled coarsening. Overall, Sanicro 25 shows good resistance to long-term steam oxidation at 700 °C due to the formation of a continuous Cr-rich protective scale. However, this protection is accompanied by chromium depletion and local near-surface microstructural changes, which should be considered when assessing the long-term stability and service performance of this steel under high-temperature steam conditions. Full article

Peri-implantitis treatment is challenging because of the complex micro- and nanostructured topography of implant surfaces. No standard debridement protocol exists. In this study, we compared five debridement methods used on heavily contaminated titanium implants that were explanted due to peri-implantitis. Twenty-five explanted implants (five per group) were treated with a carbon fiber ultrasonic insert, a polyetheretherketone (PEEK) ultrasonic insert, a rotating titanium brush, an erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser, or an erbium-doped yttrium, aluminum, and garnet (Er:YAG) laser. Five pristine implants were used as controls. Surface morphology was assessed by scanning electron microscopy (SEM). The Modified-Implant Debridement Visual Index (M-IDVI) was used to assess the debridement effectiveness according to SEM images. Surface elemental composition was assessed for atomic percentage (at. %) of carbon, titanium, oxygen and nitrogen using energy-dispersive X-ray spectroscopy (EDS). Mechanical methods were more effective at removing debris than laser methods. The titanium brush showed the lowest residual debris (2.33 ± 0.33) and the greatest reduction in surface carbon (Δ = −7.77 at. %). Surface titanium increased after debridement for all methods except for Er,Cr:YSGG (Δ = −5.9 at. %). Er:YAG best preserved SLA microtopography but exhibited a lower debridement efficacy (3.27 ± 0.83) than mechanical methods. No method resulted in a pristine surface. Full article

Cable wires provide a viable technical pathway for the laser additive manufacturing of high-entropy alloys (HEAs). However, the complex interplay of structural and material parameters of cable wires leads to significant variations in molten pool dynamics, which poses challenges to the fabrication of high-quality HEA coatings. To clarify the effects of these key factors on molten pool behavior, a multi-physics numerical model for the laser cladding of Al₅₀Si₆Ti₈Cr₁₂Cu₁₂Ni₁₂ cable wires was established in this study. A dedicated physical model for cable wires was developed, and the Level Set Method was employed to track fluid interfaces throughout the cladding process. Based on the proposed model, the temperature distribution, stress fields, and elemental homogeneity within the molten pool were systematically investigated. The results reveal that chromium (Cr) addition induces a viscosity reduction, and a torsional pitch of ≤4 mm is critical for achieving defect-free, compositionally uniform HEA coatings, which provides novel insights for process optimization and alloy design of cable-wire laser cladding. Full article

This study investigates the production of high-carbon ferrochrome (HCFeCr) using pre-reduced chromite pellets. Chromite ore from the Kempirsai deposit, semicoke as a reducing agent, and activated bentonite as a binder were used for pellet preparation. Pellets with a size of 12–14 mm were produced and subjected to reduction roasting at 1400 °C for 1–3 h. The results showed that increasing the roasting time promoted chromite reduction and increased the chromium metallization degree. After 3 h of roasting, the chromium metallization degree reached 43.93%. SEM analysis confirmed the formation of metallized chromium-containing phases and a porous structure favorable for subsequent smelting. Smelting experiments were carried out in a 0.1 MVA ore-thermal furnace using pre-reduced pellets. Stable furnace operation, satisfactory slag fluidity, and effective separation of metal and slag were observed. The obtained high-carbon ferrochrome contained 68.92 wt.% Cr, 1.54 wt.% Si, and 7.11 wt.% C. Chromium recovery into the alloy reached 92.17%, while the slag contained 2.14 wt.% Cr₂O₃. The specific electric energy consumption during experimental smelting was 4648.1 kWh/t of ferrochrome. Recalculation to industrial conditions showed an expected energy consumption of 3132.76 kWh/t, confirming the potential of pre-reduced chromite pellets for energy-efficient ferrochrome production. Full article

Traditional adsorbents, such as clay minerals, mainly target metal cations, which limits their effectiveness in mining soils where multiple metals and oxyanionic species coexist. To address this limitation, we evaluated amino-functionalized UiO-66-NH₂ as a stabilizing amendment capable of immobilizing both anionic and cationic metal species. This study evaluated its stabilization performance for vanadium (V), chromium (Cr), nickel (Ni), and zinc (Zn) in typical mining soils. Soil samples were amended with 1%, 2%, and 3% dosages and incubated for 50 days to systematically analyze leaching behavior, speciation transformation, and microbial community responses. At 50 days, the 1% UiO-66-NH₂ treatment reduced the leaching concentrations of V, Cr, Ni, and Zn by 90.42%, 59.72%, 90.12%, and 90.71%, respectively. Although Cr showed its highest reduction efficiency under the 3% treatment, the 1% dosage provided a practical compromise for multi-metal stabilization rather than a universal optimum. The stabilization process was primarily driven by surface complexation and ion exchange, which facilitated the transformation of metals into stable oxidizable forms. The amendment increased soil organic matter (SOM) and cation exchange capacity (CEC), triggering competitive adsorption and increasing the mobility of Zn and Ni. Microbial profiling revealed a successional shift toward resilient taxa, specifically the proliferation of Actinomycetota and Arthrobacter. These findings established that a 1% UiO-66-NH₂ amendment provides a robust and ecologically compatible strategy for the sustainable remediation of complex mining-impacted environments. Full article

Thermal spray technologies are widely used in aerospace, gas turbine, and automotive industries, where nickel-based superalloys are valued for their mechanical strength and resistance to oxidation and corrosion at elevated temperatures. This study investigates the microstructure and tribological performance of Ni–5Al/Inconel 625 composite coatings deposited on AISI 1025 steel using wire arc spraying, aiming to provide a cost-effective alternative to bulk superalloys and more advanced thermal spray techniques. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, while surface roughness, microhardness, and dry sliding wear behavior were evaluated using ball-on-disk tests against Al₂O₃ counter-bodies. Confocal microscopy and three-dimensional triboscopic imaging were employed to analyze wear-track morphology and friction behavior. X-ray diffraction (XRD) analysis confirmed the presence of a predominantly intermetallic Ni₃Al (γ′) phase with secondary NiAl in the bond coat, indicating significant interdiffusion between the NiAl bond coat and the Inconel 625 top coat. The top coat exhibited a face-centered cubic (FCC) γ Ni-based solid solution. The coatings exhibited a typical lamellar structure with low porosity (2%–3%) and oxide content of 12%–15%, primarily chromium and niobium oxides located at splat boundaries. Abrasion, combined with interlamellar decohesion, was identified as the dominant wear mechanism. Post-deposition polishing reduced surface roughness from 11.9 µm to 2.12 µm, leading to a 2.5-fold reduction in wear volume and a significant decrease in debris pile-up. The corresponding specific wear rates were approximately 9.3 × 10⁻⁵ mm³/Nm and 3 × 10⁻⁵ mm³/Nm for the as-prepared and polished conditions, respectively, which are within the range reported in the literature for similar coatings. These findings demonstrate that wire arc-sprayed Ni–5Al/Inconel 625 coatings, particularly after polishing, offer improved wear resistance while maintaining cost-effectiveness, making them a promising alternative for tribological applications. Full article

Heavy metal pollution remains a major global environmental challenge due to persistent ecological risks and potential threats to food safety. Microbial remediation and phytoremediation represent sustainable alternatives to conventional treatments; however, their effectiveness is strongly influenced by number of factors including nutrient availability. This review critically examines how nutritional regulation governs microbial metabolism, plant physiological responses, and rhizosphere interactions to enhance heavy metal transformation and removal. Metal bioavailability depends on type, concentration, soil pH, redox potential, and microbial processes. Interventions including fertilizers, chelating agents, inoculation with arbuscular mycorrhizal fungi and plant-growth-promoting rhizobacteria enhance phytoremediation processes through regulating plant nutrient and heavy metal uptake, while selection between ammonium/nitrate changes rhizosphere pH consequently affects plant metal uptake. Similarly, nutrients, i.e., phosphate, iron, zinc and manganese competitively affect metal uptake. Organic amendments enhance phytostabilization, especially for selenium and mercury, while enhancing chromium reduction. Sulfur-reducing bacteria precipitate metals as insoluble sulfides with 90% efficiency. In addition, soil amendments including plant-growth-promoting rhizobacteria, arbuscular mycorrhizal fungi, and metal-chelating agents can be strategically used to enhance the phytoextraction from metal from contaminated soils. We suggest that the future integration of modern approaches such as multi-omics and cisgenesis supported by artificial intelligence tools can help to accurately predict the efficiency of nutrient regulation strategies and their remediation outcomes, thereby supporting evidence-based soil management. Full article

Chromium-containing ferroalloy wastes represent an important secondary resource; however, chromium is mainly bound in thermodynamically stable spinel phases, which complicates its reduction. Unlike previous studies focusing on pure oxide systems, this work demonstrates the enhanced destabilization and subsequent reduction of MgCr₂O₄ spinel in real ferroalloy wastes under SHS conditions, revealing a non-monotonic relationship between activation time and reduction efficiency. A critical activation threshold (~30 min) was identified, beyond which particle agglomeration suppresses reaction kinetics. Powder mixtures based on HShP and KEK wastes with Al–C–Si reducing agents were mechanically activated for 10–120 min and subsequently subjected to SHS at 950 °C. The combustion parameters, phase composition (XRD), microstructure (SEM), and elemental composition (EDS) were analyzed. The results show a pronounced non-monotonic dependence of combustion temperature and front velocity on activation time, with maximum values at ~30 min (1920 °C and 1.10 mm/s for HShP; 1765 °C and 0.98 mm/s for KEK). XRD analysis indicates that MgCr₂O₄ was not detected within the XRD detection limits and that the highest relative amount of metallic chromium phase (~8% for HShP and ~6.8% for KEK) was observed at the same activation time. SEM observations reveal the formation of a more dispersed and porous structure, while EDS indicates an increase in chromium content up to ~15 wt.% in local regions. At longer activation times, overgrinding and agglomeration reduce process efficiency. Mechanical activation enhances chromium reduction through improved mass transfer, with an optimal activation time of ~30 min. The chromium reduction efficiency was evaluated using a semi-quantitative approach based on XRD phase analysis and supported by EDS data, allowing comparative assessment of reduction efficiency rather than absolute extraction values. These results highlight the existence of a critical mechanochemical activation threshold governing the balance between enhanced reactivity and agglomeration effects. Full article

Coagulation-based technologies are increasingly recognized as key for controlling fluoride and hexavalent chromium in urban water and wastewater. Combined geogenic and industrial sources often drive chronic exposure and create an underrecognized public health burden. This review synthesizes current knowledge on the occurrence, speciation, and toxicology of F⁻ and Cr(VI) in urban systems, links regulatory targets to health outcomes, and critically examines conventional, advanced, and electrochemical coagulation processes for their removal under realistic water-quality conditions. Mechanistic sections describe how aluminum-, iron-, magnesium- and zirconium-based coagulants, including pre-polymerized and composite formulations (e.g., IPC-type coagulants, PSiFAC-Mg, ZrCl₄), remove fluoride via Al–F complexation, Al–F–OH co-precipitation, ion exchange, and sweep flocculation, while Cr(VI) control relies on Fe(II)-mediated reduction to Cr(III), followed by adsorption and co-precipitation with metal hydroxides. The review assesses how water chemistry and operating conditions affect single- and multi-contaminant removal, highlighting competition among fluoride, Cr(VI), nutrients, and other oxyanions. Performance data from bench-, pilot-, and selected full-scale studies show that optimized coagulation and electrocoagulation can substantially reduce fluoride and Cr(VI) (to drinking-water-relevant levels) in diverse urban waters, but also reveal persistent issues of sludge generation and stability, residual metals, process robustness, and cost. The review identifies priorities, including long-term urban-scale assessments, low-toxicity green coagulants, life-cycle and health impact assessments, and real-time coagulation control for fluoride and Cr(VI). Full article

This study investigates the thermodynamic and kinetic features of chromium reduction from chromium ore using complex Fe–Si–Cr and Al–Si–Cr alloys as reducing agents for the refined ferrochrome production. The thermodynamic probability of Cr₂O₃ reduction by silicon and aluminum was evaluated using thermodynamic equilibrium calculations based on reference thermodynamic data, including determination of the standard Gibbs free energy change over the studied temperature range. The results showed that both reduction routes are thermodynamically feasible, while aluminum exhibits a higher affinity for oxygen and a greater reducing capacity. The thermal behavior of chromium ore and its mixtures with Fe–Si–Cr and Al–Si–Cr alloys was studied by differential thermal and thermogravimetric analysis. The use of Al–Si–Cr, especially in briquetted form, was found to shift several thermal transformation stages to lower temperatures and to reduce the apparent activation energy of the high-temperature interaction stages compared with Fe–Si–Cr-containing mixtures. The obtained results indicate that Al–Si–Cr alloy is a promising complex reductant for intensifying chromium recovery and improving process conditions in refined ferrochrome production. Full article