Search Results (75)

The development of stable, non-toxic electrolytes is essential for electrodepositing large-area coatings. This study presents a novel low-cyanide electrolyte, offering a viable alternative to traditional cyanide-based solutions for the electroplating of gold–copper alloys. Compared to conventional baths, the new formulation offers safer handling and environmental compatibility without compromising performance. Electrolyte compositions were optimized via cyclic voltammetry, and coatings were deposited using direct current, pulse current, and reverse pulse current methods. The novel low-cyanide electrolyte system achieved a 99.1% reduction in cyanide use compared with the commercial formulation. Coatings produced with pulse current and reverse pulse current deposition exhibited structural, morphological, and mechanical properties comparable to those obtained from cyanide-based electrolytes. Overall, the low-cyanide electrolyte represents a safer, high-performance alternative to traditional cyanide-based systems. Full article

In rocketry today, conventional hypergolic propellant combinations typically use hydrazine-derived fuels and oxidizers based on nitrogen tetroxide. Due to their high toxicity and consequently expensive handling, safer alternatives, so-called “green hypergolics”, are currently being developed. The ionic liquid-based fuels [EMIM][SCN], HIP_11 and HIM_30, paired with highly concentrated hydrogen peroxide as an oxidizer, are three candidates for such green hypergolics, which are currently under research at the German Aerospace Center (DLR). These combinations have been shown to exhibit reliable hypergolic ignition. For a better understanding of the reaction process and to assess the risks in working with these propellants, it is desirable to determine their combustion products. A test setup was designed to extract the gaseous combustion products from hypergolic drop tests. The gas samples were analyzed using Fourier-transform infrared spectroscopy and the gaseous combustion products were determined from the infrared spectra. Additional tests with varied oxidizer concentration or alternative fuels were conducted to further investigate detailed aspects of the findings. It was concluded that [EMIM][SCN], HIP_11 and HIM_30 produce very similar sets of combustion products with hydrogen peroxide, including water vapor, carbon dioxide, carbon monoxide, hydrogen cyanide and sulfur dioxide. Finally, the combustion products were compared to the substances produced when thermally decomposing the fuels. This confirmed that the previously detected substances were caused by a reaction between hydrogen peroxide and the fuels, rather than by their thermal decomposition due to heating. Full article

The rapid consumption and disposal of electronic waste due to technological innovations and changes in living commodities are causing the development of a significant environmental challenge. Among the components of these wastes, spent printed circuit boards are particularly considered to be among the most valuable owing to their content of precious metals, such as gold first and potentially platinum, which may be available in a lower proportion. Effective methods as part of gold recovery strategies by industries and policymakers are developed and envisioned from economic and environmental perspectives. Currently, cyanidation dominates global gold production from e-waste due to its selectivity for gold. The high toxicity of cyanide, however, poses serious environmental issues, leading thiosulphate leaching to emerge as a non-toxic and promising alternative for gold extraction. Its industrial viability has been demonstrated by Barrick Gold Corporation at the Goldstrike site with the pretreatment of acidic or alkaline pressure oxidation. This review introduces bioleaching as a promising economic and environmentally friendly process for gold extraction. This review explores thiosulphate leaching of gold as an alternative to conventional cyanidation, with a particular focus on biothiosulphate production by adapted microorganisms. The factors that affect the pretreatment, chemical reaction mechanism, and design engineering are discussed. The consumption of thiosulphate was identified as one of the main challenges, restricting the reliability of the process. Various solutions for the reduction of its consumption and relevant process costs were discussed, with a particular examination from the engineering aspect of the process design and scalability to industrially relevant operating conditions by using bioreactors adapted to large pulp density loads of electrical waste. Full article

The cyanidation of precious metals from ores and secondary resources has been classified as a hazardous process due to the release of toxic gases. The use of environmentally friendly and cost-effective processes is a suitable alternative to cyanidation. Thiourea leaching has been shown to be one of the best alternative reagents to cyanide. The present work aims to evaluate the efficiency of the thiourea leaching of gold and silver from pretreated pyrite cinders. The use of pre-chemical activation prior to leaching helped to increase the amount of free gold and silver particles. A preliminary leaching test led to the selection of Fe₂(SO₄)₃ as a suitable oxidizing agent for Au and Ag leaching. To select suitable leaching parameters, the response surface methodology (RSM) was used to optimize some parameters that can considerably affect sulfuric acid–thiourea leaching and identify the greatest interaction between them. The optimized parameters of 30 g/L thiourea, 10% pulp density, pH = 1, and 50 °C over 4 h of leaching time allowed for Au and Ag recoveries of 98.31 and 88.57%, respectively. Full article

This study investigates the impact of KNO₃-based salt bath nitriding on the microstructure, hardness, and corrosion resistance of 20MnCr5 steel. The nitriding process was conducted at 600 °C for 3 h and resulted in a nitrogen diffusion zone with a thickness that varied across the specimen, reaching a maximum of 70 μm. X-ray diffraction (XRD) analysis revealed no detectable nitrides, indicating nitrogen primarily occupied interstitial sites in the ferrite lattice and caused a lattice expansion of ~0.16%. Nanoindentation measurements showed an 80% increase in surface hardness (10.2 GPa) compared to the substrate (5.67 GPa), attributed to the solid solution strengthening mechanism. In contrast, however, an 18% decrease in Young’s modulus was observed near the surface, likely due to nitrogen-induced lattice distortions and crystal defects. Electrochemical tests in a 3.5 wt.% NaCl solution showed improved corrosion resistance, with the nitrided specimen exhibiting a 58% lower corrosion rate (1.275 mm/year) compared to untreated steel (3.04 mm/year). Despite a cathodic shift in corrosion potential, indicating localized susceptibility, the surface layer acted as a partial barrier to chloride ingress. The study demonstrates that KNO₃-based salt nitriding is an environmentally friendly alternative to cyanide-based processes that offers good surface hardness and corrosion resistance, but needs to be further optimized. Full article

This study compares gold leaching using sodium cyanide (NaCN) with alternative YX500 and Jinchan reagents. The research object was a gold–sulfide polymetallic ore (Republic of Kazakhstan) with a gold content of 0.38 g/t. The closed flotation beneficiation experiment resulted in a concentrate with an 81.40% recovery and a 5.3 g/t gold grade. The resulting concentrate was subjected to oxidizing roasting to completely oxidize the sulfides and mineral grains of arsenopyrite, pyrite, and carbon. A comparative evaluation of leaching showed that the gold recovery from the roasted concentrate using alternative YX500 and Jinchan reagent solutions was comparable to that using NaCN, with the recoveries at approximately the same level of 86.5%. The differential analysis of the obtained multiplicative multifactor Protodyakonov–Malyshev model made it possible to determine the apparent activation energy of the process using the Arrhenius equation, which eliminates the widely used graphical model. In the proposed method of kinetic experiment planning, the time differentiation of the Kolmogorov–Erofeev equation is mandatory, determining it as a partial dependence on the duration and multiplicative equation for all transformations to determine the activation energy of the process at any given conversion value and other operative factors. The variation range of the apparent value of the activation energy of the gold leaching process, from 0.718 to 78.0 kJ/mol, indicates that the limiting stage of this process is the solid-phase diffusion of CN ions from the outside to the center of the grain material. Full article

The thiosulfate–glycine–copper system has emerged as a promising alternative for gold recovery, offering significant advantages over cyanidation and ammoniacal thiosulfate leaching. Recognizing the limitations of thiosulfate degradation in ammoniacal systems, this study focused on optimizing the thiosulfate–glycine–copper system for gold recovery using an auriferous ore with (10 g t⁻¹) of Au. The ore was associated with aluminosilicates such as grossular (64%) and clinochlore (12%). Leaching conditions were systematically varied, including thiosulfate (0.5–1 M), glycine (0.3–1.75 M), copper sulfate (2–10 mM), pH (9.3–10.5), temperature (20–60 °C), 6 h, and potassium permanganate concentrations (0.004–0.04 M), and dosing intervals were also optimized. Thus, the best conditions were thiosulfate (0.7 M), glycine (1.75 M), copper sulfate (5 mM), pH 9.3, 60 °C, and permanganate addition every 2 h. This system achieved 89.3% gold recovery in just 6 h, comparable to cyanidation (89.8% in 24 h) and ammoniacal thiosulfate (58% in 6 h), but without generating toxic effluents, such as in the cyanidation process. Additionally, a gold dissolution mechanism was proposed, highlighting glycine’s role in stabilizing cupric ions and enhancing thiosulfate efficiency. This study underscores the thiosulfate–glycine–copper system as a sustainable and effective method for gold recovery. Full article

In order to meet the ever-growing needs of society, modern agriculture must develop sustainable farming and livestock production. Crops need phosphorus, a macronutrient found in soils, but they are only able to utilize small quantities of it. Chemical phosphate fertilizers are ineffective and environmentally harmful. The use of microorganisms (bacteria, yeast, filamentous fungi, and microalgae) that synthesize phytases is a promising and environmentally friendly alternative to chemical fertilizers. Phytases are also needed as feed additives in animal husbandry to overcome phosphorus deficiency for animal growth and development. Phytases are phosphatases that catalyze the release of phosphorus from phytate by stepwise hydrolysis. The broad substrate specificity, optimal pH range, higher thermal stability, and specific efficiency of fungal phytases make them interesting enzymes for agricultural applications. They improve and stimulate the growth and development of plants and animals by releasing inorganic phosphorus and producing siderophores, organic acids, hydrogen cyanide, ammonia, and phytohormones. Phytases are crucial for enhancing phosphorus use in farming and decreasing phosphorus waste’s environmental effects. This paper addresses key challenges in modern farming, such as the inefficient utilization of phosphorus from soil and the environmental harm caused by chemical fertilizers, and provides a comprehensive overview of recent advances in the research of fungal phytases. Available scientific data have been synthesized to highlight the potential of phytase use in agriculture. This review outlines key areas for future research, including the development of phytase variants with improved functionality. The potential integration of fungal phytases into sustainable agricultural practices is underlined, in contrast to previously published work focused primarily on their biochemical properties. The review offers new insight into the possible applications of micromycete phytases as a critical factor for sustainable agriculture in the future. Full article

For over a century, cyanidation has been a highly effective method for extracting gold from gold-bearing sources. However, due to environmental, health, and safety concerns associated with this process, considerable efforts have been devoted to exploring the use of alternative, less toxic, and environmentally friendly reagents. In this study, a comparative cyanide and ethaline deep eutectic solvent (DES) leaching study of gold from the Witwatersrand gold tailings was undertaken. A Statistical Design of Experiments (DOE) was used for the screening and optimization of significant process factors to achieve optimal gold extraction. The factors investigated include the reagent concentration, leaching time, pulp density, and solution temperature. The subsequent gold recovery from leach solutions was undertaken using activated carbon (AC). Mineralogical analysis by X–ray diffraction (XRD) showed that the tailings consisted of quartz (72.13%), muscovite (7.49%), chlorite (2.65%), pyrophyllite (1.50%), clinochlore (1.30%), and other trace minerals. Mineral liberation analysis (MLA) employing the Sparse Liberation–Dual Zoom (SPL-DZ) method showed that gold was associated with iron oxides (Fe₂O₃, Fe₃O₄). Fire assay analysis (FAA) showed that the bulk tailings had a grade of 0.32 g/t Au. Ethaline was found to be the most efficient reagent, achieving up to 71.9% gold extraction, thereby exceeding the 46.9% gold extraction obtained via the cyanidation process. Moreover, gold recovery using AC from ethaline leach solution was 75%. The high gold extraction from tailings using ethaline suggests a potentially feasible alternative to the traditional cyanidation process, particularly for the processing of gold locked in iron oxide phases, offering the advantages of low toxicity, cost-effectiveness, and ease of preparation. Full article

The respiratory activities of mitochondrial complexes I, II, and IV were analyzed in permeabilized Rhodotorula mucilaginosa cells and isolated mitochondria, and the kinetic parameters K_0.5 and V_max were obtained. No difference in substrate affinities were found between mitochondria and permeabilized cells. The activities of the components of the mitochondrial respiratory chain of the Antarctic yeast R. mucilaginosa M94C9 were identified by in-gel activity and SDS-PAGE. The mitochondria exhibited activity for the classical components of the electron transport chain (Complexes I, II, III, and IV), and supercomplexes were formed by a combination of the respiratory complexes I, III, and IV. Unfortunately, the activities of the monomeric and dimeric forms of the F1F0-ATP synthase were not revealed by the in-gel assay, but the two forms of the ATP synthase were visualized in the SDS-PAGE. Furthermore, two alternative pathways for the oxidation of cytosolic NADH were identified: the alternative NADH dehydrogenase and the glycerol-3-phosphate dehydrogenase. In addition, an NADPH dehydrogenase and a lactate cytochrome b2 dehydrogenase were found. The residual respiratory activity following cyanide addition suggests the presence of an alternative oxidase in cells. Full article

The transmembrane nitrate reductase (Nar) is the first enzyme in the dissimilatory alternate anaerobic nitrate respiratory chain in denitrifying bacteria. To date, there has been no real-time method to determine its specific activity embedded in its native membrane; here, we describe such a new method, which is useful with the inside-out membranes of Paracoccus denitrificans and other denitrifying bacteria. This new method takes advantage of the native coupling of the endogenous NADH dehydrogenase or Complex I with the reduction of nitrate by Nar through the quinone pool of the inner membranes of P. denitrificans. This is achieved under previously reached anaerobic conditions. Inner controls confirming the specific Nar activity determined by this new method were made by the total inhibition of the Nar enzyme by sodium azide and cyanide, well-known Nar inhibitors. The estimation of the Michaelis–Menten affinity of Nar for NO₃⁻ using this so-called Nar-JJ assay gave a K_m of 70.4 μM, similar to previously determined values. This new Nar-JJ assay is a suitable, low-cost, and reproducible method to determine in real-time the endogenous Nar activity not only in P. denitrificans, but in other denitrifying bacteria such as Brucella canis, and potentially in other entero-pathogenic bacteria. Full article

In recent years, noticeable progress has been made in the development of alternative extraction systems characterized by greater sustainability. In this context, deep eutectic solvents (DESs) have emerged as a promising alternative to the conventional solvents commonly used in metal extraction. This work focuses on investigating the extraction of lanthanum in an aqueous solution of sulfuric acid using a deep eutectic solvent, employing molecular dynamics simulations (MD). The structural characteristics of the solvent and its interactions with the components of the aqueous solution are explored. In this study, tetraethylammonium bromide (TEABr) is combined with ethylene glycol (EG) to form a DES, in which sodium cyanide (NaCN) is subsequently solubilized. According to the results obtained from the MD simulation, the primary interactions in the DESs are established through hydrogen bonds between the bromine and the hydrogens of the methyl group of tetraethylammonium at 3.5 Å, as well as between the bromine and the hydrogens of the methylene group of ethylene glycol at 3.5 Å. Similarly, the main interactions between the binary DES and sodium cyanide occur through the hydrogens of the hydroxyl group of EG and the carbon of cyanide at 1.7 Å, and between the oxygen of the hydroxyl group of EG and the sodium at 2.5 Å. In the acidic solution, the primary interaction is highlighted between the lanthanum ion and the oxygen of the bisulfate at 2.8 Å. Additionally, it is observed that the interaction between the DES and the aqueous solution occurs between the lanthanum and the oxygen of the hydroxyl group of EG, as well as between the lanthanum and the carbon of cyanide at 4.4 Å. It is important to note that, when increasing the temperature from 25 to 80 °C, the interaction distance between the lanthanum and the carbon of cyanide decreases to 2.4 Å, suggesting a possible correlation with the increase in lanthanum extraction, as experimentally observed. Overall, this study underscores the importance of considering the fundamental structural interactions of the DES with the lanthanum acid solution, providing an essential theoretical basis for future experimental investigations. Full article

Phosphorus constitutes a crucial macronutrient for crop growth, yet its availability often limits food production. Efficient phosphorus management is crucial for enhancing crop yields and ensuring food security. This study aimed to enhance the efficiency of a short-chain polyphosphate (PolyP) fertilizer by integrating it with plant growth-promoting bacteria (PGPB) to improve nutrient solubilization and wheat growth. Specifically, the study investigated the effects of various bacterial strains on wheat germination and growth when used in conjunction with PolyP. To achieve this, a greenhouse experiment was conducted in which the wheat rhizosphere was amended with a short-chain PolyP fertilizer. Based on the morphological aspect, eight bacteria, designated P1 to P8, were isolated and further characterized. Plant growth-promoting traits were observed in all bacterial strains, as they presented the ability to produce Indole Acetic Acid (IAA) in significant amounts ranging from 7.5 ± 0.3 µg/mL to 44.1 ± 2 µg/mL, expressed by B. tropicus P4 and P. soyae P1, respectively. They also produced ammonia, hydrogen cyanide (HCN), and siderophores. Their effect against the plant pathogen Fusarium culmorum was also assessed, with P. reinekei P2 demonstrating the highest biocontrol activity as it presented a total inhibitory effect. Additionally, some strains exhibited the ability to solubilize/hydrolyze phosphorus, potassium, and zinc. In vivo, the initial growth potential of wheat seeds indicated that those inoculated with the isolated strains exhibited elevated germination rates and enhanced root growth. Based on their plant growth-promoting traits and performance in the germination assay, three strains were selected for producing the best results, specifically phosphorus hydrolyzation/solubilization, zinc solubilization, IAA production, HCN, and siderophores production. Wheat seeds were inoculated by drenching in a bacterial suspension containing 10¹⁰ CFU/mL of log phase culture, and an in planta bioassay was conducted in a growth chamber using three selected strains (Pseudomonas soyae P1, Pseudomonas reinekei P2, and Bacillus tropicus P4), applied either individually or with PolyP on a P-deficient soil (28 mg/kg of P Olsen). Our findings demonstrated that the combination of Pseudomonas soyae P1 and PolyP achieved the highest shoot biomass, averaging 41.99 ± 0.87 g. Notably, applying P. soyae P1 or Bacillus tropicus P4 alone yielded similar results to the use of PolyP alone. At the heading growth stage, the combination of Bacillus tropicus P4 and PolyP significantly increased the Chlorophyll Content Index (CCI) to 37.02 µmol/m², outperforming both PolyP alone (24.07 µmol/m²) and the control (23.06 µmol/m²). This study presents an innovative approach combining short-chain PolyP with bacterial biostimulants to enhance nutrient availability and plant growth. By identifying and characterizing effective bacterial strains, it offers a sustainable alternative to conventional fertilizers. Full article

In thiosulfate leaching of gold, the copper-ammonia complex serves as an oxidant and catalyst. This study examined the impact of magnetizing the copper-ammonia thiosulphate lixiviant solution on gold leaching from refractory oxidized ores. Magnetization reduced surface tension, improved wettability and infiltration, and enhanced the diffusion of leaching agents. It also increased dissolved oxygen content and boosted the catalytic efficiency of copper-ammonia complexes. These changes led to more efficient gold extraction, with column leaching showing a 4.74% improvement in extraction rates compared to non-magnetized methods and a 3.67% improvement over cyanide processes. These findings suggest that magnetized copper-ammonia thiosulphate lixiviant is a promising, environmentally friendly alternative to cyanide for refractory oxidized gold ores. Full article

Waste-conductive silver pastes are considered an important secondary resource. The recovery of metals from waste-conductive silver pastes have high economic value. The traditional cyanidation method has serious environmental pollution, while the thiosulfate method is green, environmentally friendly, and has become a viable alternative for metal extraction. The exposure of thiosulfate complexes to ultraviolet (UV) light has been found to generate metal sulfides, and this can be used to realize the recovery of valuable metals. In this study, the extraction of silver and copper from conductive silver pastes was systematically performed using sodium thiosulfate, and the effects of sodium thiosulfate concentration, solid-to-liquid ratio, and extraction and photolytic process temperatures were investigated. The photolytic products were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. After 4 h of UV irradiation with a wavelength of 254 nm, 87% of silver and 49% of copper were recovered and transformed into silver and copper sulfide, respectively. This study demonstrates that thiosulfate can be applied in combination with UV photolysis technology to recover valuable metals in an environmentally friendly manner. Full article