Hydrochloric Research Articles

On the fate of protonated chloroformates in the gas phase: a competition between forming HCl and chloroformic acid.

Chloroformates are prevalent in the atmosphere due to their utilization as fuel additives and industrial solvents. These species may undergo interactions with atmospheric water resulting in protonated chloroformates. This study delves into the gas-phase dissociation of these protonated species. Tandem mass spectrometry was employed to scrutinize the unimolecular dissociation of protonated methyl (1), ethyl (2), neopentyl (3), and phenyl chloroformate (4). Notably, 1 and 4 exhibited HCl loss, yielding CH3OCO+ and C6H5OCO+, respectively, with 1 additionally generating neutral methanol and ClCO+. 4 additionally loses CO and CO2. In contrast, 2 and 3 each only exhibit a single fragmentation channel, with 2 losing C2H4 to generate protonated chloroformic acid and 3 generating protonated 2-methylbutene by losing neutral chloroformic acid. Density functional theory at the B3LYP/6-311+G(d,p) level of theory was employed to explore minimum energy reaction pathways for each ion, and CBS-QB3 single-point energy calculations were added to provide reliable energetics. The Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of the rate constants for selected competing processes were carried out to link theory and experiment. One common unimolecular process observed was the 1,3-H shift of the proton from the carbonyl oxygen to the ester oxygen before dissociation.

Corrosion Behavior of Ferritic Stainless Steel Joint Brazed with Ni-Based Brazing Foil in Hydrochloric Acid Solution

Corrosion Behavior of Ferritic Stainless Steel Joint Brazed with Ni-Based Brazing Foil in Hydrochloric Acid Solution

CHEMICAL CONSTITUENTS, TRADITIONAL USES AND PHARMACOLOGICAL PROPERTIES OF MADHUCA LONGIFOLIA: A REVIEW

Plant extracts and their derivatives are used by almost 80% of the world's population for the treatment of various infections and disorders. The current review was based on the chemical constituents, traditional uses and pharmacological properties of Madhuca longifolia. The Madhuca longifolia (Mahua) Symmachus indica is a huge deciduous tree native to Nepal, India, and Ceylon. It is also known as the Butter nut tree and is a member of the Sapotaceae family. The height of an M. longifolia tree can reach up to 70 feet. The fruiting period of the tree begins between the ages of 8 and 15, and can last up to 60 years. When ripe, the fruits have a greenish yellow colour and are oval in shape [4]. Sugars, vitamin A, ascorbic acid, thiamine, riboflavin, Ca, P, Fe, Mg, Cu, anthocyanins, betains, salts of malic and succinic acid, and many other vitamins and minerals can be found in flowers. It is the rich source of quercetin, 3-O-lrhamnosid, stigmasterol, n-hexacosanol, n-octacosanol, carotene, myricitin, erthrodiol, 3-caproxyolcan-12-en-28-ol, 3-galactoside and Xanthophylls. It was traditionally utilized in bronchitis, diabetes, rheumatism, haemorrhage, ulcer, tonsillitis, pharyngitis, and spongy gums etc. In conclusion, Madhuca longifolia is reported to be effective as antioxidant, analgesic, anti-pyretic, anti-inflammatory, immunosuppression, anti-ulcer, anti-hyperglycaemic, anti-neoplastic and anthelmintic.

The Assessment of Heat-treated Turkish Type Dry Fermented Sausage (Sucuk) with Some Mixed Probiotic Lactic Acid Bacteria

T his study aims to obtain a combination of probiotic strains resistant to stress conditions, which good effect the qualitative properties of heat-treated sausage. Lactic acid bacteria (LAB) strains were identified by matrix-assisted laser desorption-ionization-time of flight mass spectrometry (MALDI-TOF MS) after phenotypic evaluation and evaluated for probiotic potential including acid and bile salt tolerance, antibiotic resistance, and antibacterial activity. All tested Lactiplantibacillus plantarum strains showed high antibacterial activity. L. plantarum (PeE2) and additionally two Enterococcus strains with the best probiotic properties were selected among the strains. Except for the control group, 6 different sucuk doughs were prepared using them as mixed cultures. The ripened sucuk doughs (18 h, 4 ºC) were subjected to fast-drying (30 min, 60 ºC), heat-treated (64 ºC of inner temperature) and rapid-drying (10 min, 75 ºC) stages. The quality characteristics of samples were determined during storage (days 7, 14, and 21). Coliform bacteria growth ≤1 log cfu/g determined on the final day of storage. The lowest TBARS value was determined in L. plantarum +E. faecium (1:1 ratio) mixed culture. Regarding L* and a* color values, lower results were observed in the control group during storage. Using probiotic culture significantly affected textural values, taste and general acceptability (p<0.05) and contributed to the quality parameters. The result of the study may support the development of a new approach for using new probiotics in meat products.

Isolation, selection, and evaluation of characteristics of potential Bacillusstrains for probiotic products

In the human digestive tract, there resides a very large number of microorganisms, including more than 400 different species of bacteria. Probiotics are defined as live bacteria that when introduced into the body in sufficient quantities will produce beneficial health effects. Probiotics (commonly known as digestive enzymes) are not drugs but are classified as nutritional supplements. In this study, we aim to investigate the probiotic properties of 2 strains of Bacillus bacteria isolated from fecal samples of healthy people, without the use of antibiotics or probiotic products for at least 1 month. The basic properties investigated include the hemolytic ability of bacteria, tolerance to artificial gastric acid and bile salt, and sensitivity to antibiotics. Out of a total of 72 isolates, 2 potential Bacillus strains were selected that did not cause hemolysis, were able to survive and survive in the harsh environment of the digestive system, and were sensitive to antibiotics commonly used for humans. On that basis, we initially evaluated the safety and potential application of these 2 strains to probiotic products.

Experimental Study for the Influence of Methyl Substituent's Position on Quinoline for Inhibition of Aluminium Corrosion in Hydrochloric Acid

Experimental Study for the Influence of Methyl Substituent's Position on Quinoline for Inhibition of Aluminium Corrosion in Hydrochloric Acid

Demulsification of Pickering Emulsions by Chemical Dissolution of Stabilizers.

Demulsification of particle-stabilized oil-in-water emulsions is crucial in diverse fields such as treatment of produce water, recovery of valuable products of Pickering emulsion catalysis, and so on. In this work, we investigated a facile method for destabilizing emulsions by dissolving stabilizer particles by the introduction of acid or base. Nanoellipsoidal hematite-stabilized decane-in-water emulsions are destabilized by dissolving hematite with oxalic or hydrochloric acid in situ. Time required for complete demulsification decreased as the acid concentration is increased. The demulsification time is typically on the order of a few hours for the chosen protocol. Similarly, the silica-stabilized decane-water emulsion is demulsified by the addition of aqueous sodium hydroxide. Demulsification kinetics is presented as the temporal change of the emulsion volume with time. Emulsion volume decreases in two stages: an initial slow decrease followed by an exponential decrease. Scanning electron microscopy analysis shows that the stabilizing particles are completely dissolved and recrystallized as salts of respective kinds. An estimate of the desorption free energy suggests that particle size should be reduced to a few nanometers for inducing destabilization. This work describes a facile method to destabilize oil-in-water emulsion, and it can be generalized to any other particle-stabilized emulsions by choosing appropriate chemical reagent for dissolution.

Optimizing hematite filter cake treatment using reducing agents

In drilling operations, the formation of a filter cake is crucial for well stability, but its removal post-drilling is essential to restore rock formation productivity. This study focuses on hematite-based filter cakes and investigates factors influencing their solubility and removal, addressing a significant knowledge gap in the field. The research methodology involves examining the effects of various factors, including types and concentrations of reducing agents, temperature, particle size, and treatment duration, on the dissolution process. Notably, Nuclear Magnetic Resonance (NMR) tests are employed to assess the treatment's impact on core porosity. Among the diverse reducing agents examined, ferrous chloride emerges as the optimal choice for effectively enhancing hematite solubility. Particularly, a composite solution of ferrous chloride (10 wt.%) and hydrochloric acid (6 wt.%), was highly efficient demonstrated by exhibiting rapid solubilization of hematite filter cakes. A removal efficiency of approximately 99%, with a parallel enhancement in core permeability was achieved. NMR tests reveal the treatment's success in reinstating the porosity system, which had undergone reduction due to drilling fluid particles. Crucially, the solution exhibits a considerably lower corrosion rate than concentrated hydrochloric acid, highlighting its potential to mitigate environmental concerns while ensuring efficient filter cake removal. The findings of this research provide valuable insights into optimizing post-drilling operations, balancing environmental sustainability and operational efficiency. The identified composite solution offers a promising approach to efficient filter cake removal while mitigating environmental concerns associated with corrosion. Overall, this study contributes to advancing the understanding and practice of well productivity enhancement in the oil and gas industry.

Potential of Bioactive Protein and Protein Hydrolysate from Apis mellifera Larvae as Cosmeceutical Active Ingredients for Anti-Skin Aging

This study aimed to extract bioactive proteins and protein hydrolysates from Apis mellifera larvae and assess their potential application in cosmetics as well as their irritation properties. The larvae were defatted and extracted using various mediums, including DI water, along with 0.5 M aqueous solutions of sodium hydroxide, ascorbic acid, citric acid, and hydrochloric acid. Subsequently, the crude proteins were hydrolyzed using the Alcalase® enzyme. All extracts underwent testing for antioxidant activities via the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) and Griess assays. Anti-aging properties were evaluated in terms of anti-collagenase and anti-hyaluronidase effects. Irritation potential was assessed using the hen’s egg chorioallantoic membrane (HET-CAM) test. The results revealed that the sodium hydroxide extraction showed promising outcomes in terms of yield, protein content, and effectiveness in inhibiting hyaluronidase, with the highest inhibition at 78.1 ± 1.5%, comparable to that of oleanolic acid. Conversely, crude protein extracted with ascorbic acid and its hydrolysate showed notable antioxidant and collagenase-inhibitory activities. Remarkably, their anti-collagenase effects were comparable to those of ascorbic acid and lysine. Additionally, it demonstrated safety upon testing with the CAM. In conclusion, the findings provided valuable insights into the utilization of A. mellifera larval proteins as active ingredients with a wide range of cosmeceutical applications, particularly due to their antioxidant, anti-aging, and low irritation properties, which hold significant promise for anti-skin wrinkles.

Leaching behaviour of limonite ores from Lapaopao, Southeast Sulawesi, Indonesia: Effect of mineralogy and acid types

An atmospheric leaching study of limonite ores from Lapaopao, Southeast Sulawesi, using hydrochloric acid (HCl), nitric acid (HNO<sub>3</sub>), and sulfuric acid (H<sub>2</sub>SO<sub>4</sub>) has been performed. The objectives of this study were to analyze the effect of ore mineralogy and acid types on the dissolution behavior of minerals and the leaching rate of Ni and Co at atmospheric pressure conditions. Mineralogical analysis was carried out using optical microscopy, scanning electron microscopy (SEM), and X-ray diffractometry (XRD), while the ore's chemical composition was determined by using X-ray fluorescence spectrometry (XRF) and atomic absorption spectrophotometry (AAS). Mineralogically, the limonite ores are dominated by goethite, followed by gibbsite, talc, and lizardite, with less amounts of hematite and quartz. Analysis results of solid residues revealed that mineral dissolution order was determined as follows: goethite > lizardite > gibbsite> hematite > talc> quartz. The results of the leaching experiment exhibited that the order of leaching rates of Ni in the three ores samples using three different acids were found as follows: Ore-1 > Ore-2 > Ore-3. Comparison of HCl, HNO<sub>3</sub>, and H<sub>2</sub>SO<sub>4</sub> as the lixiviants for the leaching of limonite ores demonstrated that HCl was the most reactive acid, followed by HNO<sub>3</sub> and then H<sub>2</sub>SO<sub>4</sub>. This might be due to the differences in mineralogical nature and reactivities of acids during the leaching process.

Chronic autoimmune gastritis and its relation to megaloblastic anemia – Main histopathological and pathophysiological characteristics

Chronic autoimmune gastritis is a sustained inflammation of the stomach, characterized by being immunologically mediated against intrinsic factor-producing parietal cells, leading to nutritional deficiencies that may result in anemia. This study investigates the prevalence and underlying mechanism of anemia in patients with chronic autoimmune gastritis, focusing on iron deficiency anemia and megaloblastic anemia due to vitamin B12 deficiency. A bibliographic review was carried out on the subject, in databases of scientific relevance and verified by peers, whose inclusion criteria allowed only studies relevant to the subject, published in the last five years, which establish a relationship with chronic autoimmune gastritis and anemia. Thus, the exclusion criteria left out studies on chronic gastritis due to other etiologies, those cases not related to anemia, or other studies not relevant to the general objective. In the pathophysiological framework, there is an autoimmune destruction of gastric parietal cells, which leads to a reduction in the secretion of hydrochloric acid and intrinsic factor, essential for the absorption of vitamin B12 and iron, predisposing to iron deficiency and megaloblastic anemia. Histological examination reveals gastric atrophy with loss of glands, lymphocytic infiltration, and presence of plasma cells. Symptoms include dyspepsia, loss of appetite and loss of appetite.

The durability of slag and tannery sludge based geopolymer corroded by acid and base solutions

The current treatment (landfill, composting, and incineration) of chromium-containing sludge can contaminate soil, surface water and groundwater. In this study, tannery sludge and granulated blast furnace slag was chosen to make a geopolymer and its ability to resist acid and alkali was investigated by immersing them in different solutions for 28d. The experimental results showed that when pH value increased from 1.0 to 13.0, the compressive strength linearly increased from 36.7MPa to 68.4MPa while the porosity decreased from 4.37% to 3.4%. The results of NMR, SEM and FIR showed that the H+ in HCl acid solution depolymerized the three-dimensional network structure of the geopolymer and acicular product (CaCl2) was generated, which leaded to the increase in small pores and large pores. However, when immersed in alkaline solution the secondary polymerization occurred and more C-S-H appeared, making the geopolymer denser. In addition, the environmental benefits of the geopolymer were investigated and the results showed that the leaching concentration ranges of total chromium and Cr(VI) were 1.21mg/L~0.97mg/L and 0.04mg/L~0.06mg/L, both of which were far below the requirement of standards. The CO2 emission was 8.06kg/(m3Mpa), which was roughly half of the ordinary Portland cement (18kg/(m³MPa)). Therefore, the geopolymer could be a way to treat tannery sludge and the geopolymer made of tannery sludge and slag had the potential to be environmentally friendly building materials.

A technique for depositing iron, tungsten, molybdenum, and chrome in the determination of selenium and tellurium in alloy steel by ICP-AES method

Direct determination of the content of selenium and tellurium impurities in metallurgical materials by the method of inductively coupled plasma atomic emission spectroscopy (ICP-AES) is difficult due to spectral and non-spectral interference from macrocomponents present in the materials under study. The separation of micro-(Se, Te) and macro-components (Fe, W, Mo, Cr, Cu, Ni, Co) through preliminary precipitation is the goal of the study. The use of barium acetate and sodium fluoride as precipitants are shown to provide an effective separation of Se and Te from Fe, W, Mo, and Cr (the content in the analyzed solution is less than 0.1 wt.% of the original) and partial separation from Cu, Ni, and Co (the content in the analyzed solution from 25 to 55 wt.% of the original). Optimal conditions for the deposition of macrocomponents (Fe, W, Mo, Cr) and inhibition of the process of coprecipitation of selenium and tellurium on sediments of macrocomponents for their subsequent ICP-AES determination were determined. The optimal pH for the precipitation of macrocomponents equals 1. The optimal mass of precipitants (barium acetate and sodium fluoride) is 10 and 3 g, respectively. To inhibit the process of coprecipitation of selenium and tellurium on sediments of macrocomponents, it is proposed to use hydrofluoric acid. The optimal volume of hydrofluoric and hydrochloric acids for inhibiting the process of coprecipitation of analytes on sediments of macrocomponents was determined (3 and 6 cm3, respectively). The developed procedure for separating micro-Se, Te from macro-components was tested on standard samples of alloyed steels using the «spike» method. The technique is characterized by satisfactory accuracy and reproducibility, the limit of determination of analytes after separation of macrocomponents is 10–3 wt.%.

Leaching kinetics of ash impurities from aphanitic graphite by combining dual-ultrasound and hydrochloric acid–potassium hydrogen fluoride

The hydrochloric acid-fluoride salt is useful for purifying graphite. Ultrasonic-assisted technique can significantly reduce the leaching time and improve the leaching efficiency. Compared with single-frequency, dual-frequency ultrasound has the advantages of high energy efficiency and wide cavitation area. In this study, the combination of a dual-frequency ultrasound-assisted technique and hydrochloric acid–potassium hydrogen fluoride leaching agent was proposed for the leaching of aphanitic graphite to remove impurity minerals. First, the effects of probe-type ultrasonic power, tank-type ultrasonic power, temperature, HCl concentration, ultrasonication time, and KHF2 concentration on the purification efficiency of impurities from aphanitic graphite with the assistance of dual-frequency ultrasound were investigated. It was found that the combination of dual-frequency ultrasound and hydrochloric acid–potassium hydrogen fluoride can reduce the ash content of aphanitic graphite from 13.02 % to 1.02 % with an ash removal rate of 94.17 %. Second, volumetric reaction models and unreacted shrinkage nucleation models were used to fit the kinetics of impurities from aphanitic graphite with dual-frequency ultrasound-assisted HCl-KHF2 leaching. Kinetic analysis shows that the volumetric reaction model with chemical control was better to fit the leaching process. This is consistent with the calculation results of the activation energy of the reaction (Ea = 58.13 kJ/mol). Finally, laser particle size analyzer, X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) were used to analyze the fugacity of impurity minerals during the process of dual-frequency ultrasound-assisted HCl-KHF2 leaching. It was revealed that combining ultrasonic cavitation fragmentation with chloric acid–potassium fluoride generated SiF4 with high solubility, thereby removing silica-bearing impurities more efficiently. The challenges in further reducing ash content from 1.02 % in the leached concentrate of aphanitic graphite could be attributed to the existence of titanium-bearing mineral impurities on the surface of graphite particles and the presence of silica-bearing minerals between graphite carbon layers.

Effect of the surface coating of carbonyl iron particles on the dispersion stability of magnetorheological fluid

The dispersion stability of carbonyl iron particle (CIP)-based magnetorheological fluid (MRF) is improved by CIP, which particle is etched with hydrochloric acid (HCl) to form porous structure with many hydroxyl groups and subsequently coated with silane coupling agents that have varying chain lengths. The microstructures, coating effect and magnetism of the CIPs were examined using the Scanning Electron Microscopy, Automatic Surface and Porosity Analyzer (BET), Fourier-Transform Infrared Spectroscopy, Thermogravimetric Analysis and Vibrating Sample Magnetometer. Furthermore, the rheological properties and dispersion stability of the MRFs were assessed using a Rotating Rheometer and Turbiscan-lab. The results revealed that the nanoporous structure appeared on the CIPs and the specific surface area increased remarkably after being etched by hydrochloric acid. Additionally, as the chain length of the silane coupling agent increases, the coated mass on the particles increases, the the density and the saturation magnetization of particles decreased, and the coated particles with different shell thicknesses were obtained; without a magnetic field, the viscosity of MRF prepared by coated particles increase slightly, due to the enhancement of special three-dimensional network structure; under a magnetic field, the viscosity of the MRF decreased distinctly; the sedimentation rate of MRF decreased from 58 to 3.5% after 100 days of sedimentation, and the migration distances of the MRFs were 22.4, 3.7, 2.4, and 0 mm, with particle sedimentation rates of 0.149, 0.019, 0.017, and 0 mm/h, respectively. The MRF with high dispersion stability was obtained, and the etching of CIP by HCl and the proper chain length of the coating of silane coupling agent were proved effective manners to improve the dispersion stability of MRF.

Effect of Recycled Concrete Aggregate Addition on the Asphalt Mixtures Performance: ITZ Area, Microstructure, and Chemical Analysis Perspectives

The importance of environmental consciousness and sustainability is increasing among transportation governing bodies worldwide. Many government bodies are concerned with maximizing the usage of recycled substances in road construction. Therefore, assessing the effect of recycled materials consumption is essential, mainly when designing new ‘green’ pavement types. The primary objective of this study is to investigate the impact of different treatments on improving the interfacial transition zone (ITZ) of coarse recycled concrete aggregate (CRCA) and its application in asphalt mixes. Such an aim is accomplished by enhancing its physical and mechanical characteristics, as well as its microstructure. The surface morphology, chemical composition, and intermix phases of the ITZ area and calcium silicate hydrate (CSH) compounds for CRCA were evaluated using scanning electron microscopy (SEM), an energy-dispersive X-ray analyzer (EDAX), and X-ray diffraction analysis (XRD). The performance of asphalt mixtures that included treated and untreated CRCA was also examined using different tests. It was found that heat treatment is an effective technique for enhancing the ITZ. However, cracks were seen in the mortar of CRCA when exposed to high temperatures (500 °C), which adversely affects the characteristics of the mortar. Acid treatment appeared to be an effective approach for improving the ITZ area. Nevertheless, the treatment that used acetic acid, a weak acid, was more effective than HCl acid, a strong acid. The outcomes revealed that the ITZ microstructure is significantly enhanced under different treatment types; however, microstructure improvements mainly included increased surface homogeneity and CSH compounds and a reduced Ca/Si ratio. It was also found that the asphalt mixtures with different proportions of untreated CRCA exhibited enhanced resistance to rutting. Furthermore, their tensile strength ratio (TSR) values were above the minimal level requirements. Moreover, the asphalt mixture with 30% CRCA, which was treated with various treatment methods, demonstrated a significant improvement in the mixtures’ mechanical properties; therefore, its application is highly successful and an environmentally friendly solution.

Chemical, electrochemical, and quantum investigation into the use of an organophosphorus derivative to inhibit copper corrosion in acidic environments

In order to protect the copper against corrosion, a novel corrosion inhibitor known as diphenyl ((2-aminoethyl) amino) (4-methoxyphenyl) methyl) phosphonate (DAMP) was developed. Acid solutions of HCl and H2SO4 were the aggressive solutions employed in this study. Analysis using the FT-IR, 1H-NMR, 31P-NMR, 13C-NMR and BET confirmed that the DAMP was successfully synthesized. The anti-corrosion capabilities of DAMP are evaluated using a combination of chemical, electrochemical and quantum studies. The DAMP has been found to be crucial in preventing the corrosion of copper in both HCl and H2SO4 acid. This was obviously implied by the observation that the corrosion rate of copper in acid solutions decreased when DAMP was added. It is significant to note that 180 ppm produced the highest levels of inhibiting efficiency (96.6% for HCl and 95.2% for H2SO4). The tendency of DAMP to adsorb on the surface of copper through its hetero-atoms (O, N, and P) is the main factor for the anti-corrosion capabilities of DAMP. Results from SEM/EDX tests supported this. The actual adsorption takes place via various active centers, physical and chemical mechanisms that are coordinated with the estimated quantum parameters. Additionally, the adsorption of DAMP adheres to the Langmuir isotherm.

Novel routes for synthesis of rare earth oxychlorides

Rare earth oxychlorides (REOCl) have received significant interest for their potential applications in chloride ion conductors, catalysts, luminescent materials due to their unique and special properties. Many synthesis methods were reported for their production including solid-state, flux-assisted, and sol-gel techniques. The present study introduces two straightforward solid state synthesis routes for synthesizing desired oxychlorides. In the first route, REOCl is prepared by roasting of a mixture of hydrous rare earth chloride (RECl3.xH2O) and rare earth oxide (RE2O3) powder. The second route involves, initial curing followed by roasting a portion of RE2O3 with hydrochloric acid (HCl) for production of the oxychlorides. For both routes, the optimal process conditions were first defined for LaOCl synthesis. Subsequently, the refined conditions of second method were successfully applied to the synthesis of NdOCl and SmOCl. The thorough mineralogical and morphological analysis of the obtained products under these conditions provides valuable insights into their characteristics and potential applications.

Application of functionalized carbon nanofibers as a modifying additive to motor oil

Due to the widespread of lubricants, improving their tribological characteristics remains an important practical task. Among the promising modifying additives, carbon nanomaterials attract special attention. Such materials are found to improve the antifriction characteristics of lubricants and oils. In the present research, carbon nanofibers were synthesized via catalytic pyrolysis of a mixture of light hydrocarbons (C2-C4) over the NiCu catalyst. In order to form functional groups on the surface of carbon nanofibers, they were treated with diluted acids HCl, HNO3, and H2SO4 as well as with concentrated HNO3. The functionalized samples were comprehensively characterized by a set of physicochemical methods including atomic absorption spectroscopy, scanning and transmission electron microscopies, low-temperature nitrogen adsorption, X-ray photoelectron spectroscopy, temperature-programmed desorption/oxidation, and Raman spectroscopy. As defined, the surface oxygen concentration in the samples varies from 3.5 to 16.3 at.%. It was shown that the addition of modified carbon nanofibers to a motor oil leads to an improvement in its tribological characteristics. In particular, the most effective additive was the sample treated with diluted HNO3. The motor oil with this modifying additive exhibited the heating temperature decreased by 10 °C and the contact spot area on the stationary body decreased by 20 %.

Selective Recovery of Gold from E-Waste Recycling Plants’ Waste Fractions: Waste-to-Resource Transition

Electronic waste grows globally at a rate of 5% annually, which makes electronic waste recycling (WEEE recycling) an urgent task aimed at achieving (i) environmental protection and (ii) the preservation of mineral resources through the re-introduction of strategic metals into the market. As it turns out, WEEE recycling produces further waste, called WEEE secondary waste, which still contains valuable metals such as gold, silver, and copper. This study assessed the economic viability of recovering these metals and identified the most promising targets and approaches. WEEE secondary waste produced at a plant in southern Europe was sampled and examined for this purpose. The study methods included an ANOVA (analysis of variance) and an OCCP (orthogonal central composition plan). Over 90% gold, silver, and copper extraction was achieved with hydrochloric acid leaching in sodium hypochlorite with sodium chlorite as an oxidizing agent at 60 °C. The significance of the variation in the response for each factor, calculated using the Yates algorithm, demonstrates that by excluding sodium chloride and optimizing the doses of hydrochloric acid and sodium hypochlorite, gold can be selectively recovered through the leaching process. The scenario of HCl (2.5M)/NaClO (5%) leaching results in the maximum extraction effect of Au (91.6%) at the lowest concentrations of Ag and Cu (37–44%).