Precious Metals Research Articles

Is VAT Incurred during the Recycling Process Involving Precious Metal Weight Accounts? – A German Perspective

In this article the authors examine precious metal weight accounts in the context of German VAT Law. Such a topic is highly relevant to the framework of transactions involving precious metals, yet it is often overlooked in existing literature due to the lack of specific provisions. In Germany, the only source of guidance is a letter from the Federal Ministry of Finance. In the article, two scenarios are analysed, one within Germany and one involving an intra-Community transaction.

Health effects of indium compounds in animal experiments.

Before 2000, very little attention had been paid to the health effects of indium, a rare metal, because there was very little information in the literature on its toxicity. A fatal case of indium-tin oxide (ITO) inhalation occurred in 2001, followed by concerns regarding occupational exposure to indium compounds and their health effects. Epidemiological studies and case reports have established a causal relationship between the inhalation of insoluble indium compounds, mainly ITO and the development of lung damage. This review has focused on the results of animal studies of ITO and other insoluble indium compounds. Available data indicate that insoluble indium compounds such as ITO, indium arsenide (InAs), indium phosphide (InP), copper indium gallium, and diselenium (CIGS) solar cell materials are toxic to the lungs of animals. In addition to lung damage, ITO nanoparticles have been found to cause kidney damage, while InAs, InP, and ITO cause testicular damage. Furthermore, InP has demonstrated compelling evidence of its carcinogenic potential in long-term inhalation studies using rats and mice, which was evident in rats exposed to ITO. Based on the results of these animal experiments, the International Agency for Research on Cancer evaluated InP as probably carcinogenic to humans (Group 2A) and ITO as possibly carcinogenic to humans (Group 2 B). Hence, occupational exposure of humans to insoluble indium compounds not only causes lung damage, but also lung carcinogenesis and kidney or testicular damage. Greater attention should be directed towards human occupational exposure to insoluble indium compounds.

Amides Enable Room-Temperature CO2 Conversion: Simple Organic Molecules Challenging Metal Catalysts.

The conversion of carbon dioxide (CO2) into valuable chemicals has been intensively pursued for sustainable chemistry. It is highly desirable to achieve the conversion under ambient conditions using organocatalysts instead of precious or pollutive metal catalysts. Herein, we disclose a new class of organocatalysts for direct C(sp)-H carboxylation with CO2. Amide molecules such as N-methylacetamide and valerolactam behave as efficient bifunctional catalysts to promote the conversion of aromatic alkynes to propiolic acids. In particular, the simple organic catalysts enable the reaction to occur at room temperature, which has been achieved only with complex transition metal catalysts prior to this report. In the presence of the optimal base of Cs2CO3, the adjacent nitrogen and oxygen sites of the amide group concurrently activate CO2 and C(sp)-H and position them in favor of C-C coupling, affording a high catalytic activity on par with those of transition metal catalysts. The work sheds new light on the catalytic chemistry of CO2 and also illustrates the great potential of discovering new organocatalysts from simple molecules.

Nanoadsorbents; advanced tailored strategies for precious metals recovery from waste sources

Nanoadsorbents; advanced tailored strategies for precious metals recovery from waste sources

Catalytic Hydrogenolysis of Lignin into Serviceable Products.

ConspectusLignin, a major component of lignocellulosic biomass, accounts for nearly 30% of organic carbon on Earth, making it the most abundant renewable source of aromatic carbon. The valorization of lignin beyond low-value heat and power has been one of the foremost challenges for a long time. On the other hand, aromatic compounds, constituting a substantial segment of the chemical industry and projected to reach a market value of $382 billion by 2030, are predominantly derived from fossil resources, contributing to increased CO2 emissions. Integrating lignin into the aromatic chemical supply chain will offer a promising strategy to reduce the carbon footprint and boost the economic viability of biorefineries. Thus, depolymerizing lignin biopolymers into aromatic chemicals suitable for downstream processing is an important starting point for its valorization. However, owing to lignin's complexity and heterogeneity, achieving efficient and selective depolymerization that yields desirable, isolable aromatic monomers remains a significant scientific challenge.The structure of lignins varies significantly in terms of subunits and linkages across plant species, leading to considerable differences in their reactivity, in the distribution of resulting monomers, and in their subsequent utilization. In this context, this Account highlights our recent studies on the catalytic hydrogenolysis of lignin into serviceable products for preparing valuable materials, fuels, and chemicals. First, we designed a series of catalytic systems for lignin hydrogenolysis specifically tailored to the structural features of lignin from wood, grass, and certain seed coats. To reduce reliance on expensive commercial catalysts like Pd/C, Ru/C, and Pt/C, we advanced heterogeneous metal catalysts by shifting from high-loaded nanostructured metals to low-loaded, atomically dispersed metals and replacing precious metals with nonprecious alternatives. This approach significantly reduces the cost of catalysts, enhances their atomic economy, and improves their catalytic activity and/or selectivity. Then, using the developed catalysts, phenolic monomers tethering a distinct side chain were selectively generated from the hydrogenolysis of lignin (from various plants), achieving yields close to the theoretical maximum. The high selectivity allowed the separation and purification of monomeric phenols from lignin reaction mixtures readily. To gain deeper insights into the cleavage of lignin C-O bonds, we designed deuterium-incorporated β-O-4 mimics (dimers and one polymer) for a mechanistic study, which excluded the pathways involving the loss of linkage protons and led to the proposal of a concerted hydrogenolysis process for β-O-4 cleavage. Finally, to enable the utilization of depolymerized lignin phenolic monomers, unconventional feedstocks in the current chemical industry, we developed a series of methods to transform them into valuable bioactive molecules, functional materials, and high-energy fuels. Overall, these contributions opened new avenues for converting lignin into serviceable products, encompassing upstream processing and downstream applications.

Advances in the Energy‐Saving Electro‐Oxidation of 5‐Hydroxymethylfurfural to 2,5‐Furandicarboxylic Acid

AbstractAs a pivotal bio‐based building block, 2,5‐furandicarboxylic acid (FDCA) holds immense and broad application potential in the chemistry industry. Its polymeric derivative, polyethylene furandicarboxylate (PEF), emerges as an appealing alternative to conventional petroleum‐based polyethylene terephthalate (PET). The electrochemical route for oxidizing 5‐hydroxymethylfurfural (HMF) into FDCA presents significant advantages over the thermochemical processes, without the requirements of high temperature, high pressure, chemical oxidants, and precious metal catalysts, featuring higher energy efficiency. Furthermore, the electrosynthesis of FDCA at the anode can be synergistically integrated with selective reduction reactions at the cathode, enabling the simultaneous production of two desirable value‐added products and further enhancing overall energy utilization efficiency. This work reviews the advancements in electrocatalytic HMF to FDCA (EHTF), encompassing catalyst design, reaction mechanisms, coupling strategies, and reactor configurations. It also indicates the challenges and opportunities of EHTF and provides insights into the future development directions.

Phase Equilibria and Trace Element Deportments in Fe–O–Al2O3–SiO2 Slags and Molten Copper Matte at 1473 K (1200 °C), Fixed p(O2) and p(SO2), and Silica/Magnetite Saturation

Abstract Understanding the role of major components of electric waste during smelting of these materials to recover valuable trace metals is poorly constrained by experimental data. In this study, phase equilibria and trace element deportments were studied at 1473 K (1200 °C) in conditions of combined sulfide concentrate and electric and electronic equipment waste processing in batchwise submerged lance smelting. In this system, liquid slag domain is limited by silica and magnetite saturation boundaries or primary phase fields at all alumina concentrations from alumina-free slags to silica-spinel double saturation. The impact of alumina concentration in slag at fixed oxygen and sulfur dioxide partial pressures on the distributions of Ag, Cu, In, Pb, and Sn was studied. Elemental concentrations in slag, matte, and solid magnetite (a Fe–Al spinel solid solution) were measured using electron probe microanalysis and laser ablation-ICP-mass spectrometry techniques. The observed impact of alumina on the distribution coefficient of silver, copper, and indium favored the matte phase at silica and magnetite saturation but lead and tin behaved differently within different primary phase fields as a function of alumina concentration.

Voltage-Gated 90° Switching of Bulk Perpendicular Magnetic Anisotropy in Ferrimagnets.

Unraveling the mechanism behind bulk perpendicular magnetic anisotropy (PMA) in amorphous rare earth-transition metal films has proven challenging. This is largely due to the inherent complexity of the amorphous structure and the entangled potential origins arising from microstructure and atomic structure factors. Here, we present an approach wherein the magneto-electric effect is harnessed to induce 90° switching of bulk PMA in Tb-Co films to in-plane directions by applying voltages of only -1.2 V. This manipulation is achieved by voltage-driven insertion of hydrogen atoms into interstitial sites between Tb and Co atoms, which serves as a perturbation to the local atomic structure. Using angle-dependent X-ray magnetic circular dichroism, we find that the anisotropy switching originates from the distortion of the crystal field around Tb, which reorients the alignment of Tb orbital moments. Initially aligned along Tb-Co bonding directions, the easy magnetization axis undergoes reorientation and switches by 90°, as substantiated by ab initio calculations. Our study not only concludes the atomic origin of Tb-Co atom bonding configuration in shaping bulk PMA but also establishes the groundwork for electrically programmable ferrimagnetic spintronics, such as controlling domain wall motion and programming artificial spin textures.

Electroreduction-driven distorted nanotwins activate pure Cu for efficient hydrogen evolution.

Precious metals such as Pt are favoured as catalysts for the hydrogen evolution reaction (HER) due to their excellent catalytic activity. However, the scarcity and high cost of precious metals have prompted researchers to explore cheaper alternatives such as Cu. Nevertheless, Cu shows poor catalytic performance due to weak binding with intermediates. Here the catalytic activity of pure Cu is activated via electroreduction-driven modification of the local structure, achieving a HER catalytic performance superior to commercial Pt/C catalysts for working current densities greater than 100 mA cm-2 in acid electrolyte. Activation involved two steps. First, polycrystalline Cu2O nanoparticles were prepared via pulsed laser ablation, resulting in grain boundaries within the Cu2O particles as observed using electron microscopy. Next, the Cu2O particles were electroreduced to pure Cu, inducing the formation of distorted nanotwins and edge dislocations. These local structures induce high lattice strain and decrease the Cu coordination number, enhancing the interaction between Cu and intermediates-as calculated using density functional theory-leading to the excellent catalytic activity and durability of the catalyst. Our observations show that low-cost pure Cu can be a promising HER catalyst for large-scale industrial applications.

Multiepoch Observations of the Nearby Spiral Galaxy NGC 3938 with the Chandra X-Ray Observatory

Abstract We present an analysis of two epochs of ACIS observations of the SA(s)c spiral galaxy NGC 3938 with the Chandra X-ray Observatory. The total exposure time of the observations was 95 ks, with a limiting unabsorbed luminosity of ≈1038 erg s−1 assuming a distance of 22 Mpc. A total of 47 discrete merged sources from both epochs were detected at the ≈3σ level or greater with the D25 radius. We demonstrate that at the time of the Chandra observations the nucleus was not detected. We connect the detected sources to counterparts in other wavebands to the degree possible. Based on the two epochs, we identify three variable sources and an additional two that may have varied between the two observations. We do not formally detect any of the five historical supernovae that have occurred in NGC 3938. The luminosity function of NGC 3938 is compared to a recent compilation of 38 galaxies, and we identify a potentially significant problem with the “known” distance to NGC 3938. Star formation rate and metallicity values are also computed; the star formation rate is highly dependent on the adopted distance. The metallicity appears to lie in the range of 8.2–9.2, consistent with values from other work. We include in an appendix a short discussion of the sources that lie in Chandra’s field of view but lie outside of NGC 3938.

PAST NAVLI TEXNOGEN CHIQINDILAR TARKIBIDAN NODIR METALLARNI AJRATIB OLISH TEXNOLOGIYASINI TADQIQ QILISH

This article investigates the technology for extracting rare metals from low-grade technogenic waste. The authors examine the need for effective methods of processing technogenic waste to minimize their impact on natural resources and extract rare metals. The article analyzes the physical-chemical processes, chemical reactions, and new technologies used for extracting rare metals. Specifically, the efficiency of extraction, economic aspects, and ecological significance of these processes are discussed.

Controllable Detachment of Organic Ligands on Ultrathin Amorphous Nanosheets Tailors the Electron-Aggregation for Accelerated pH-Universal Hydrogen Reaction.

Tailoring the local environment of catalyst surface has emerged as an effective strategy to enhance the reaction kinetics involving multiple intermediates. For hydrogen evolution reactions (HER), the driving factors for hydrogen aggregation and migration which are poorly understood in depth affects the reaction kinetics especially over a wide pH range. Inspired by the selectivity of the catalyst surface microenvironment for intermediates, an interfacial electrocatalyst composed of Ru ultrafine nanocatalysts anchored onto monolayer amorphous (a-WCoNiO) nanosheets with electron-rich microenvironment induced by an organic oleylamine ligand is designed to realize high-performance pH-universal HER. This Ru/a-WCoNiO possesses impressively low overpotentials of -13, -14, and -14mV at 10mA cm-2 in 0.5m H2SO4, 1m KOH and 1m PBS, respectively, ranking among the best HER catalysts reported to date. Benefiting from the electron-rich microenvironment, the Ru/a-WCoNiO exhibits record-high turnover frequency (TOF) and mass activity (MA), which is more than 47.9 times higher than that of commercial 20% Pt/C. Importantly, other precious metals are loaded on a-WCoNiO and enhancing their mass current density for pH-universal HER. It is believed that this developed approach of organic modifiers tailored local microenvironment has practical significance and advantages for designing other high-performance catalysts.

The Potential Role of Africa in Green Hydrogen Production: A Short-Term Roadmap to Protect the World’s Future from Climate Crisis

The global need for energy has risen sharply recently. A global shift to clean energy is urgently needed to avoid catastrophic climate impacts. Hydrogen (H2) has emerged as a potential alternative energy source with near-net-zero emissions. In the African continent, for sustainable access to clean energy and the transition away from fossil fuels, this paper presents a new approach through which waste energy can produce green hydrogen from biomass. Bio-based hydrogen employing organic waste and biomass is recommended using biological (anaerobic digestion and fermentation) processes for scalable, cheaper, and low-carbon hydrogen. By reviewing all methods for producing green hydrogen, dark fermentation can be applied in developed and developing countries without putting pressure on natural resources such as freshwater and rare metals, the primary feedstocks used in producing green hydrogen by electrolysis. It can be expanded to produce medium- and long-term green hydrogen without relying heavily on energy sources or building expensive infrastructure. Implementing the dark fermentation process can support poor communities in producing green hydrogen as an energy source regardless of political and tribal conflicts, unlike other methods that require political stability. In addition, this approach does not require the approval of new legislation. Such processes can ensure the minimization of waste and greenhouse gases. To achieve cost reduction in hydrogen production by 2030, governments should develop a strategy to expand the use of dark fermentation reactors and utilize hot water from various industrial processes (waste energy recovery from hot wastewater).

Investigating the Structure of Detachment Faulting and Its Role in Ore Formation: The Kallintiri Detachment System and the Associated Polymetallic Ore Deposit (Rhodope, NE Greece)

The Kallintiri area (SW Byala Reka–Kechros Dome, Rhodope) hosts a polymetallic (critical, base, and precious metals) ore deposit, tectonically controlled by the late Eocene–Oligocene, top-to-SW Kallintiri Detachment System. The earliest structure associated with the Kallintiri Detachment is a ductile shear zone at the interface between the high-grade footwall gneisses of the Lower and Intermediate Rhodope Terranes. The detachment zone encompasses the uppermost part of the gneisses and the ultramylonitic Makri Unit marble. The marble is bound by a brittle–ductile shear zone at the base and a knife-sharp, low-angle normal fault at the roof, exhibiting considerable brecciation and ultracataclasite development. The hanging wall includes the Makri Unit phyllites and the overlying mid–late-Eocene–Oligocene supra-detachment sediments, which show syn-depositional slump structures and brittle deformation with low- and high-angle faulting and non-cohesive cataclasites. Extensive hydrothermal fluid circulation along the detachment zone and through NW tension gashes and high-angle faults led to pronounced silicification and ore deposition. Field observations and mineralogical and geochemical analyses revealed two primary types of ore mineralization spatially and temporally associated with different structures. Base and precious metals-rich ores are associated with the detachment, while Sb ore deposition is localized mostly within the NW-trending tension gashes and high-angle faults.

Effect on NOx and CO Reduction Performance According to the Support and the Precious Metals Used When NH3 is Supplied to H2-SCR

Effect on NOx and CO Reduction Performance According to the Support and the Precious Metals Used When NH3 is Supplied to H2-SCR

Platinum modification of metallic cobalt defect sites for efficient electrocatalytic oxidation of 5-hydroxymethylfurfural

Co3O4 possesses both direct and indirect oxidation effects and is considered as a promising catalyst for the oxidation of 5-hydroxymethylfurfural (HMF). However, the enrichment and activation effects of Co3O4 on OH− and HMF are weak, which limits its further application. Metal defect engineering can regulate the electronic structure, optimize the adsorption of intermediates, and improve the catalytic activity by breaking the symmetry of the material, which is rarely involved in the upgrading of biomass. In this work, we prepare Co3O4 with metal defects and load the precious metal platinum at the defect sites (Pt-Vco). The results of in-situ characterizations, electrochemical measurements, and theoretical calculations indicate that the reduction of Co–Co coordination number and the formation of Pt–Co bond induce the decrease of electron filling in the antibonding orbitals of Co element. The resulting upward shift of the d-band center of Co combined with the characteristic adsorption of Pt species synergically enhances the enrichment and activation of organic molecules and OH− species, thus exhibiting excellent HMF oxidation activity (including a lower onset potential (1.14 V) and 19 times higher current density than pure Co3O4 at 1.35 V). In summary, this work explores the adsorption enhancement mechanism of metal defect sites modified by precious metal in detail, provides a new option for improving the HMF oxidation activity of cobalt-based materials, broadens the application field of metal defect based materials, and gives an innovative guidance for the functional utilization of metal defect sites in biomass conversion.

Enhanced oxidative bioleaching for nickel and metal recovery from arsenic ores moves toward efficient and sustainable extraction.

The research focuses on extracting nickel and other valuable elements through oxidative bioleaching from two distinct arsenic-rich ores of varying grades. This process involved utilizing a mix of mesophilic and moderately thermophilic bacteria in shake flasks with different pulp density levels to bio-leach nickeline. Mesophilic bacteria achieved over 99% nickel dissolution from both low- and high-grade ores within 10 and 28 days, respectively, at pulp densities of 0.5% and 1%. In contrast, abiotic control and chemical tests showed significantly lower nickel dissolution rates (approximately 6.9% and 26.1% for low-grade; 10.3% and 45% for high-grade samples). Moderately thermophilic bacteria achieved complete nickel dissolution from the low-grade ore at a 0.5% pulp density, while dissolution from the high-grade ore reached approximately 63%. In comparison, abiotic controls and chemical achieved only 19% and 39% dissolution for the high-grade ore, and 21.9% and 45% for the low-grade ore, respectively. X-ray diffraction (XRD) analysis confirmed the formation of scorodite as a secondary phase due to arsenic solubilization from primary minerals in the presence of iron. Kinetic modelling revealed that the bioleaching of the low-grade ore was predominantly controlled by a mixed reaction mechanism, whereas chemical factors limited the bioleaching rate of the high-grade ore. This research underscores the efficacy of oxidative bioleaching using mixed bacterial cultures and highlights its potential for efficiently extracting nickel and other valuable metals (cobalt and copper) from arsenic-bearing ores under controlled pulp density conditions.

Enhanced copper extraction from waste printed circuit boards using glycine after supercritical methanol pre-treatment: Process optimization, leaching kinetics, and thermodynamic analysis.

The disposal of waste-printed circuit boards (WPCBs) poses significant environmental and health risks, as they are a major component of e-waste containing hazardous materials. However, WPCBs also contain valuable metallic elements, making them important resources for recycling. To address the dual challenge of hazardous waste management and resource recovery, sustainable approaches for metal extraction from WPCBs are imperative. The present study, thus aimed to explore the use of glycine as an environment-friendly alternative to conventional inorganic acid-leaching agents for copper extraction from WPCBs. The integration of glycine leaching with pre-treatment under supercritical conditions with methanol enhanced the copper liberation efficiency along with improved mass transfer processes. Under optimized conditions of 0.5M glycine concentration, 5% (v/v) H2O2 concentration, 1.5:100g/mL solid-to-liquid ratio, and 40°C temperature, a remarkably high copper extraction efficiency of 97.46% was achieved within a 15h leaching duration. Besides, the kinetic studies indicated a mixed-controlled reaction mechanism for the metal extraction process, with a calculated activation energy of 40.01kJ/mol. Additionally, a thorough characterization of the recovered metal-leached salt provided insights into the compound's nature and leaching mechanism. This integrated approach developed thus offers a sustainable and environment-friendly method for reducing the hazardousness of WPCBs while simultaneously extracting valuable metals, contributing to the advancement of e-waste management practices and environmental sustainability.

Resource utilization of electric arc furnace dust: Efficient wet desulfurization and valuable metal leaching kinetics investigation.

Electric arc furnace dust (EAFD) is hazardous solid waste containing valuable metals such as iron (Fe) and zinc (Zn) in large quantities. This presents a considerable recycling issue. This study proposes an integrated and efficient approach to solid waste management. The experimental results demonstrate that the EAFD slurry effectively purifies SO2 while simultaneously recovering Zn resources. The major active components for desulfurization in EAFD were found to be inc oxide and ZnFe2O4, with depletion being the main cause of reduced desulfurization performance. The maximum Zn leaching rate reached 49.35%, and SO2 100% removal was achievable under ideal leaching conditions. A shrinkage kernel model analysis of the leaching kinetics showed that the initial apparent activation energy of the Zn leaching reaction was 15.51kJmol-1, suggesting that interfacial chemical reactions were in charge of the process. Based on the experimental and characterization results, a possible mechanism for metal ions leaching during EAFD slurry desulfurization was proposed. This study presents a novel approach for the resource utilization of hazardous solid waste EAFD, offering a sustainable solution for metal recovery and pollution control.

Human Health Risk Assessment of Heavy Metals and Polycyclic Aromatic Hydrocarbons in Seafood from Southern Nigeria’s Coastal Regions

Aim: The levels of heavy metals and polycyclic aromatic hydrocarbons (PAHs) in tilapia fish, prawn, oyster and periwinkle samples from southern Nigeria’s coastal regions were evaluated to determine possible human health risk associated with consumption. Study Design: Ten (10) samples each of the selected seafood were collected from mangrove swamps along Bakana River in the study area. The samples were analyzed for nutrient levels and concentrations of toxic metals and PAHs. Methodology: The concentrations of heavy metals and PAHs in the selected seafood samples were determined using Gas Chromatography Flame Ionization Detector and Atomic Absorption Spectrophotometry. Probable human health risk associated with the seafood consumption for adult and children populations was evaluated using Estimated Daily Intake (EDI), Target Hazard Quotient (THQ) and Carcinogenic Risk (CR) assessment for heavy metals and PAHs. Results: The seafood samples showed the presence of heavy metals (Cr, Cd, Cu, Pb and Zn) but values were all below regulatory permissible limits of 0.6, 0.05, 3.0, 0.2 and 5.0 mg/kg respectively. PAH compounds (fluorene and anthracene) were below detectable limits in the seafood samples; phenanthrene was detected in all the seafood samples but highest in Tilapia fish, recording 28.32±0.05 mg/kg. Benzo (a) pyrene was below detectable limit in the investigated seafood samples. Carcinogenic Risk (CR) assessment values for heavy metals in the seafood samples were significantly (p<0.05) high for Cd, Pb, Cr and Ni in both adult and children populations. CR values for PAHs were within regulatory threshold of 10E-6 – 10E-4. Conclusion: This study revealed that individual carcinogenic potencies for heavy metals (Cd, Pb, Ni, Cr) in the seafood samples exceed the guideline screening value for human consumption, indicating high potential for carcinogenic risk. Our findings suggest that Bakana river is exposed to substantial amount of carcinogenic environmental pollutants associated with deleterious environmental and epidemiological effects.