Concentrated Sulfuric Acid Research Articles

The annual cycle and sources of relevant aerosol precursor vapors in the central Arctic during the MOSAiC expedition

Abstract. In this study, we present and analyze the first continuous time series of relevant aerosol precursor vapors from the central Arctic (north of 80° N) during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. These precursor vapors include sulfuric acid (SA), methanesulfonic acid (MSA), and iodic acid (IA). We use FLEXPART simulations, inverse modeling, sulfur dioxide (SO2) mixing ratios, and chlorophyll a (chl a) observations to interpret the seasonal variability in the vapor concentrations and identify dominant sources. Our results show that both natural and anthropogenic sources are relevant for the concentrations of SA in the Arctic, but anthropogenic sources associated with Arctic haze are the most prevalent. MSA concentrations are an order of magnitude higher during polar day than during polar night due to seasonal changes in biological activity. Peak MSA concentrations were observed in May, which corresponds with the timing of the annual peak in chl a concentrations north of 75° N. IA concentrations exhibit two distinct peaks during the year, namely a dominant peak in spring and a secondary peak in autumn, suggesting that seasonal IA concentrations depend on both solar radiation and sea ice conditions. In general, the seasonal cycles of SA, MSA, and IA in the central Arctic Ocean are related to sea ice conditions, and we expect that changes in the Arctic environment will affect the concentrations of these vapors in the future. The magnitude of these changes and the subsequent influence on aerosol processes remains uncertain, highlighting the need for continued observations of these precursor vapors in the Arctic.

Surface Modification of Cellulose Nanofiber (CNF) from Banana (<i>Musa paradisiaca</i>) Pseudo-Stem with Cetyltrimethylammonium Bromide (CTAB)

Modifying cellulose nanofiber (CNF) is necessary to improve its hydrophobic properties for broader applications. The surface of CNF from the banana pseudo-stem (Musa paradisiaca) was modified using a cationic surfactant, Cetyltrimethylammonium Bromide (CTAB). Principally, CNF surface sulfate ester group counterions are substituted for cetyltrimethylammonium (CTA+), which acts as a bulky, amphiphilic cation. Three steps produce CNF from banana pseudo-stem: delignification, bleaching, and acid hydrolysis. The acid hydrolysis process was optimized by adjusting the concentration of sulfuric acid. A 50% sulfuric acid concentration produced CNF with a size of 118 nm and the highest stability of its zeta potential value of -28.4 mV. The hydrophobicity of CNF increased after CTAB modification, as demonstrated by a change in surface charge from -28.4 mV to +3.63 mV. The modified CNF50-CTAB had a contact angle of 45.5º. In addition, CNF50-CTAB was unstable in water and formed stable colloidal suspensions in chloroform.

Electrochemical dissolution of titanium under alternating current polarization to obtain its dioxide

Abstract The titanium electrode was polarized under the influence of alternating current (AC) at 50 Hz. The current density was varied between 100 and 5,000 A m−2. Initially, the titanium electrode oxidized, and then, titanium oxides were reduced during the cathodic half-cycle of the AC. When the cathodic half-cycle changes to the anodic half-cycle, titanium is oxidized to the trivalent state: Ti − 3 e ̄ → Ti 3 + {{\rm{Ti}}-3{\rm{e}}{\rm{̄}}\to {\rm{Ti}}}^{3+} . The direction of the AC changes depending on its frequency, causing the processes occurring on the electrodes to be periodically repeated. The current efficiency of the titanium electrode dissolution depends on the sulfuric acid concentration and electrolyte concentration, reaching up to 63.4% under optimal conditions. Bipolar electrodes were used during AC electrolysis. It was found that the decrease in the mass of titanium electrodes increases almost linearly at first, from 400 to 1,600 A m−2, and then more intensively within the current densities from 1,800 to 2,500 A m−2. It was shown that when using a bipolar electrode, the total mass loss of the electrodes is 1.38 times greater than the total mass loss during polarization without a bipolar electrode. The composition of the titanium dioxide obtained as a result of electrolysis was identified using physico-chemical analysis methods.

Towards Photothermal Acid Catalysts Using Eco-Sustainable Sulfonated Carbon Nanoparticles—Part II: Thermal and Photothermal Catalysis of Biodiesel Synthesis

The main goal of this work is to evaluate the ability of sulfonated carbon nanoparticles (SCNs) to induce photothermal catalysis of the biodiesel synthesis reaction (transesterification of natural triglycerides (TGs) with alcohols). Carbon nanoparticles (CNs) are produced by the carbonization of cross-linked resin nanoparticles (RNs). The RNs are produced by condensation of a phenol (resorcinol or natural tannin) with formaldehyde under ammonia catalysis (Stober method). The method produces nanoparticles, which are carbonized into carbon nanoparticles (CNs). The illumination of CNs increases the temperature proportionally (linear) to the nanoparticle concentration and exposure time (with saturation). Solid acid catalysts are made by heating in concentrated sulfuric acid (SEAr sulfonation). The application of either light or a catalyst (SCNs) (at 25 °C) induced low conversions (<10%) for the esterification reaction of acetic acid with bioethanol. In contrast, the illumination of the reaction medium containing SCNs induced high conversions (>75%). In the case of biodiesel synthesis (transesterification of sunflower oil with bioethanol), conversions greater than 40% were observed only when light and the catalyst (SCNs) were applied simultaneously. Therefore, it is possible to use sulfonated carbon nanoparticles as photothermally activated catalysts for Fischer esterification and triglyceride transesterification (biodiesel synthesis).

Research on the Hierarchical Separation of Rare Earths and Lithium from Rare Earth Molten Salt Slag

Lithium is an important non-renewable resource, and the study of the tiered separation of rare earths and lithium from rare earth molten salt slag is an important approach to solving the current global resource shortage. This article adopts a sulfuric acid leaching process and a lithium-containing solution iron lithium extraction separation process to recover lithium from rare earth molten salt slag. The method systematically investigates the impact of sulfuric acid concentration, liquid-to-solid ratio, leaching temperature, leaching time, pH, P507 concentration, phase ratio, extraction temperature, and extraction time on the lithium extraction effect and iron lithium separation effect in rare earth molten salt slag. The results show that under the conditions of a sulfuric acid concentration of 0.9 mol/L, a liquid-to-solid ratio of 8:1 mL/g, a leaching temperature of 70 °C, a leaching time of 90 min, a pH of 0.9, a P507 concentration of 50%, a phase ratio of 5:3, an extraction temperature of 30 °C, and an extraction time of 20 min, the lithium leaching rate reaches 97.8%, and the separation of iron and lithium is fully achieved. This method can efficiently recover the valuable element lithium from rare earth molten salt slag, which is of great significance for the subsequent preparation of lithium products and the realization of a closed-loop production of rare earth alloys by molten salt electrolysis.

Sulfuric acid treatment to control the microcrystalline structure of starch-based hard carbon for sodium storage

By treating starch with different concentrations of sulfuric acid, we investigated the effect of cross-linked starch-based hard carbon on the performance of sodium-ion batteries (SIBs) at various concentrations. After treatment, the optimal sample exhibits a spherical microstructure, which can provide effective active sites and enhance structural stability, thereby achieving high capacity and long cycle life for SIB electrodes. In subsequent electrochemical tests, after 100 cycles at low current density of 0.1 A g−1, the capacity of H40 remains of 306 mA h g−1. And under the high current density of 1 A g−1, the capacity of H40 can still maintain of 228 mA h g−1, exhibiting a high capacity retention rate of 89 %, which is higher than other samples. This study provides a promising approach for the large-scale production of biomass-derived carbonaceous SIBs anodes.

Synthesis of anatase powder by ilmenite digestion followed by selective thermal decomposition and leaching

This study investigates an innovative method for producing TiO2 from ilmenite ore through selective thermal decomposition and leaching. The focus lies on understanding the impact of co-existing sulfates on the decomposition temperature of TiOSO4. Insights into the decomposition mechanisms and parameters governing selective leaching efficiency are also presented. Ilmenite concentrate was digested with concentrated sulfuric acid, yielding titanium and iron sulfates. The digested cake was then calcined at different temperatures to induce thermal decomposition. Thermodynamic calculations were employed to model the decomposition reactions and investigate the influence of iron sulfates on TiOSO4 decomposition. Both thermodynamic evaluation and experimental results demonstrate that co-existing iron sulfates play a catalytic role in lowering the decomposition temperature of TiOSO4 from approximately 700°C to below 500°C, facilitating its conversion to TiO2. The calcined powder underwent selective leaching, first with water to remove soluble sulfates, followed by dilute acid to obtain a TiO2 precipitate. The precipitate was analyzed by different techniques.The XRD analysis confirmed the successful conversion of TiOSO4 to Anatase TiO2 during calcination and leaching. The SEM images show that the Anatase TiO2 powder displays a near-spherical morphology, with a particle size ranging from 50 to 200 nm. FTIR, DTA, and DTG analyses supported the thermodynamic calculations and XRD results, offering insights into the phase transformations during thermal decomposition and leaching. The thermodynamic evaluation and experimental results demonstrate that co-existing iron sulfates play a catalytic role in lowering the decomposition temperature of TiOSO4. By using the proposed method, anatase powder was successfully produced with minor impurities of iron, SiO2, and other metal oxides.

Anthropogenic Extremely Low Volatility Organics (ELVOCs) Govern the Growth of Molecular Clusters Over the Southern Great Plains During the Springtime

AbstractNew particle formation (NPF) often drives cloud condensation nuclei concentrations and the processes governing nucleation of molecular clusters vary substantially in different regions. The growth of these clusters from ∼2 to >10 nm diameters is often driven by the availability of extremely low volatility organic vapors (ELVOCs). Although the pathways to ELVOC formation from the oxidation of biogenic terpenes are better understood, the mechanistic pathways for ELVOC formation from oxidation of anthropogenic organics are less well understood. We integrate measurements and detailed regional model simulations to understand the processes governing NPF and secondary organic aerosol formation at the Southern Great Plain (SGP) observatory in Oklahoma and compare these with a site within the Bankhead National Forest (BNF) in Alabama, southeast USA. During our two simulated NPF event days, nucleation rates are predicted to be at least an order of magnitude higher at SGP compared to BNF largely due to lower sulfuric acid (H2SO4) concentrations at BNF. Among the different nucleation mechanisms in WRF‐Chem, we find that the dimethylamine (DMA) + H2SO4 nucleation mechanism dominates at SGP. We find that anthropogenic ELVOCs are critical for explaining the growth of particles observed at SGP. Treating organic particles as semisolid, with strong diffusion limitations for organic vapor uptake in the particle phase, brings model predictions into closer agreement with observations. We also simulate two non‐NPF event days observed at the SGP site and show that low‐level clouds reduce photochemical activity with corresponding reductions in H2SO4 and anthropogenic ELVOC concentrations, thereby explaining the lack of NPF.

Enhanced bioethanol production from Compositae plant stalks: Integrating dry acid pretreatment and fungal mediated biodetoxification

Compositae is an important economic plant with relatively high contents of water-soluble sugars in stalk section. The pretreatment of Compositae plant stalks quickly converts the water-soluble sugars into high titers of furan aldehydes, which inhibits the viability of consequent fermentation strains. This study used the typical Compositae plant stalks of sunflower, Jerusalem artichoke, and stevia as feedstocks for dry acid pretreatment under high solids loading, then a unique solid-state biodetoxification method was applied to degrade these high-titer inhibitors. The results showed that temperature and sulfuric acid concentration were two key parameters for enhancing pretreatment efficiency. Enzymatic hydrolysis yield of the above pretreated stalks reached up to 79.68%, 66.75% and 74.05%, respectively. For pretreated Jerusalem artichoke stalk, it contained 37.36% of cellulose, 2.72% of xylan, 3.04% of glucose, 11.64% of xylose, 20.54% of lignin, and some inhibitors (3.80% of acetate, 0.24% of HMF and 0.23% of furfural). After biodetoxification, 100% of furfural, 40% of HMF, and 36% of acetate were quickly removed by Amorphotheca resinae ZN1, which resulted in 55.57 g/L ethanol production (equivalent to 7.1% by volumetric percentage) with the yield of 55.54% from 73.59 g/L of glucose and 40.69 g/L of xylose by simultaneous saccharification and co-fermentation (SSCF). This study provides a combinational approach of dry acid pretreatment and biodetoxification for Compositae plant stalks biorefinery.

The Dissolution Behavior of Pyrite and Chalcopyrite During Low-Temperature Pressure Oxidation: Chalcopyrite Influence on Pyrite Oxidation

The research of this paper was carried out on the low-temperature (100 ± 2 °C) pressure (0.2–0.8 MPa) leaching of pyrite, chalcopyrite and their mixture. According to experiments on chalcopyrite dissolution, increasing the oxygen pressure from 0.2 up to 0.8 MPa had a slight effect on chalcopyrite dissolution. Oxygen pressure and initial sulfuric acid concentration in the range of 10–50 g/L had the greatest positive effect on the pyrite oxidation. The SEM and EDX mappings indicate the chalcopyrite and pyrite surfaces to be passivated by elemental sulfur. The oxidation degree of pyrite in its mixture with chalcopyrite increased significantly from 54.5 up to 80.3% in 0–240 min. The reaction time is relative to the dissolution of the individual mineral, while the dissolution of chalcopyrite remained virtually unchanged. The addition of Cu (II) and Fe (III) ions does not influence pyrite dissolution when chalcopyrite is added in a leaching process, which can be explained by the formation of an electrochemical link between the minerals. The positive effect of chalcopyrite addition is associated with a decreased formation of elemental sulfur on the surface of pyrite. The described method can be used for the hydrometallurgical processing of copper raw materials with increased pyrite content, as well as for the pretreatment of copper concentrates with gold-rich pyrite concentrates to increase the recovery of gold and silver.

Additive manufacturing and in vitro study of biological characteristics of sulfonated polyetheretherketone-bioactive glass porous bone scaffolds

Polyetheretherketone (PEEK), a high-performance special engineering plastic, has gradually been used in bone substitutes due to its wear resistance, acid and alkali resistance, non-toxicity, radiolucency, and modulus close to that of human bone. However, its stable biphenyl structure determines strong biological inertness, thus artificial interventions are required to improve the biological activity of fabricated PEEK parts for better clinical applications. This study developed a novel strategy for grafting bioactive glass (BAG) onto the surface of PEEK through sulfonation reaction with concentrated sulfuric acid (H2SO4), aiming to improve the bioactivity of printed porous bone scaffolds manufactured by fused deposition modeling (FDM) to meet clinical individual needs. In vitro biological study was conducted on sulfonated polyetheretherketone-bioactive glass (SPEEK-BAG) scaffolds obtained by this strategy. The results demonstrated that the optimal modification condition was a 4-hour sulfonation reaction with 1 mol/L concentrated H2SO4 at high temperature and high pressure. The scaffold obtained under this condition showed minimal cytotoxicity, and the Ca/P molar ratio, yield compressive strength, and compressive modulus of this scaffold were 2.94 ± 0.02, 62.78 MPa, and 0.186 GPa respectively. The hydrophilicity and the biomineralization ability of PEEK modified by the proposed strategy were substantially improved. The SPEEK-BAG bone scaffolds exhibited excellent biocompatible properties, suggesting that the sulfonation reaction and BAG effectively enhanced the proliferation and differentiation of osteoblasts. The presented method provides an innovative, highly effective, and customized strategy to improve the biocompatibility and bone repair ability of printed PEEK bone scaffolds for virous biomedical applications.

Cadmium recovery from acid leachates of Tunisian phosphoric acid purification residues.

The management of cadmium-rich sludges, which are pollutant residues from the phosphorus industry, including the valorization of these sludges through the selective recovery of heavy metals, is a promising prospect. However, there is still a need to develop recovery methods that are both optimized for efficiency, cost-effectiveness, and environmentally friendly. This study aims to enhance cadmium extraction from the polymetallic sludge by optimizing the processes of sulfuric acid (SA) leaching and sodiumsulfide precipitation. Key parameters including SA concentration, temperature, solid/liquid ratio, and stirring velocity were optimized to maximize the heavy metals extraction. Over 90% of the Cd and Zn present in the sludge were successfully extracted. Subsequently, investigates the selective precipitation of metal sulfide from acidic leachates (pH < 2), focusing particularly on cadmium. Through the optimization of chemical precipitation parameters (Na2S concentration, temperature, and reaction time), more than 99% of the cadmium was selectively recovered as CdS. The precipitates underwent analysis for mineralogy, chemistry, purity, and particle size. XRD analyses indicated CdS formation in "Greenockite" and "Hawleyite" forms, confirmed by SEM-EDS data, revealing fine powder consisting of micro and nanoparticles (< 0.5 µm) with varied spherical shapes.

Synthesis of New Heterocyclic Derivatives from 4-(3, 5-Dimethyl-1-phenyl-1H-pyrazol-4-ylazo)- benzoic acid

In this work pyrazolin derivatives were prepared from the diazonium chloride salt of 4-aminobenzoic acid. Azo compounds were prepared from the reaction of an ethanolic solution of sodium acetate and calculated amount of active methylene compound namely, acetyl acetone to obtain the corresponding hydrazono derivative (1). Cyclocondensation reaction of compounds (1) with hydrazine hydrate and phenyl hydrazine in boiling ethanol affording the corresponding pyrazoline-5-one derivatives of 4-aminobenzoic acid (2,3). Then compound (3) was reacted with thionyl chloride to give the corresponding acid chloride derivative(4), followed by conversion into the corresponding acid hydrazide derivative (5) carboxylic acid thiosemicarbazide (11), esters (14,15), thioesters (16,17) and amides (18,19), when treated hydrazine hydrate, thiosemicarbazide, alcohols, alkylthiol and secondary amines in dry refluxing benzene; respectively. Schiff's bases (6-8) were prepared by refluxing of compound (5) with different aldehydes and ketons, then two compounds from the Schiff's bases were cyclized with ?-mercapto acetic acid to give (9 and 10). Furthermore, 1,2,4-triazole derivative (12) have been also prepared by refluxing thiosemicarbazide derivative with sodium hydroxide solution (4%) followed acidification of the result using (10%)hydrolic acid. Moreover, a thiadiazole derivative (13) has been prepared by treatment of thiosemicarbazide derivative with concentrated sulfuric acid as cyclyzing agent. Finally, oxadiazole derivative (20) has prepared by condensation of its acid hydrazide derivative with carbon disulfide in basic medium.

Element behavior during autoclave oxidation of polymetallic sulfide flotation concentrate containing tungsten and molybdenum

In this paper, we investigate the behavior of associated elements (tungsten, molybdenum, and bismuth) contained in a sulfide gold-bearing concentrate during its autoclave oxidation. The process is studied using a sulfide flotation concentrate, crushed to a particle sieve mesh size of minus 0.045 mm and containing 22.1 g/t of gold, 133.2 g/t of silver, 2.7% of tungsten, 13% of molybdenum, and 0.7% of bismuth. The process was carried out in a 2 dm3 autoclave at a temperature of 220ºC and an oxygen partial pressure of 0.7 MPa. The concentrations of sulfuric acid and iron ions in the solution were determined by titrimetric analysis. Inductively coupled plasma atomic emission spectroscopy was used to determine the concentrations of bismuth, tungsten, molybdenum, copper, silver, and arsenic in the solution, as well as the content of bismuth, tungsten, molybdenum, copper, arsenic, lead, and iron and sulfur forms in the cake. The cake was also examined using diffraction analysis. Experiments on cyanidation of oxidized cake were carried out in the pH range of 10.0–10.5 and a NaCN concentration of 1 g/dm3 with a PuroliteS992 ion exchange resin for 24 h. Autoclave oxidation experiments showed the sulfide oxidation degree to be higher than 99%. Extraction of molybdenum into solution in the form of [MoO2(SO4)n]-(2n-2) and MoO 2+ amounted to 95%. The decrease in the solid mass led to an increase in the concentration of bismuth and tungsten in the cake, with their contents reaching 1.66% and 12.7%, respectively. The main phases in the cake were established to be scheelite, anhydrite, plumboyarosite, and bedantite. The extraction of precious metals at the subsequent cyanidation stage amounted to 97.5% of gold and 91.6% of silver. Therefore, autoclave cyanide processing of sulfide gold-containing concentrates leads to a molybdenum extraction in the autoclave oxidation solution at the level of 95%. During cyanidation, more than 90% of gold and silver are extracted. Due to the significant amount of tungsten (17%), bismuth (0.9%), lead (5.3%), and molybdenum (3.3%), the obtained cake cannot be considered a waste product.

Research on Leaching Cesium from Medium and Low Pollucite Concentrates by the Sulfuric Acid Process

Abstract With the sharp decrease in high-grade pollucite resources, medium and low grade pollucite concentrate will become the main raw material for extracting cesium in the future. The main process conditions for leaching cesium from medium- and low grade pollucite concentrate by the sulfuric acid process were studied, and the effects of the ratio of leaching liquid to solid, leaching time, leaching temperature and of leaching liquid on the leaching rate of cesium were investigated. The results show that CsAl(SO4)2·3H2O is formed from 2Cs2O·2Al2O3·9SiO2·H2O after the medium and low grade pollucite concentrates are leached by sulfuric acid. The optimum conditions for the leaching process were as follows: the concentration of sulfuric acid was approximately 3.5 mol/L, L/S≈2, the leaching temperature was 120 °C, the heat preservation time was 2.0 h, and the leaching rate of cesium exceeded 93%. The leaching residue was washed and discarded, and the leaching solution was recycled three times and then concentrated to precipitate alum. The [Cs] in the mother liquor resulting from CsAl(SO4)2·3H2O crystallization ranged from 1 g/L to 1.28 g/L, and the [Al] ranged from 0.29 g/L to 0.33 g/L, which could be recycled for leaching.

A simple and low-cost method for determination of methanol in alcoholic solutions

Methanol poisoning can occur through consumption of methanol-containing alcohols, especially in areas where production, distribution, sale and consumption of alcohol is lawfully prohibited. Due to its toxic potency, determination of methanol in alcoholic solutions is important. The aim of the present study was to develop a rapid, simple and inexpensive method for quantification of methanol in alcoholic solutions that uses minimal equipment available in most laboratories. The method developed is based microdistillation and chromotropic acid, which can be conducted without sophisticated instruments or personal. The system consists of a micro-tube suspended in a falcon tube to function as a collector. Methanol is separated from wine by microdistillation at 90°C in water bath and converted to formaldehyde in the collector. The collector contains an acidic permanganate solution that converts methanol to formaldehyde. Formaldehyde was then quantified by use of chromotropic acid in concentrated sulfuric acid. Experimental variables were optimized by using central composite design (CCD). Method detection and quantification limits were 183mgL−1 and 584mgL−1, respectively. The percent relative standard deviation (RSD%) were between 6.4 and 7.9. Accuracies were between 89.6% and 92.4%. Concentrations of methanol in five alcoholic solutions were between 2.9×104 and 3.0×104, mg/L, v/v (ppm). Due to its simplicity and cost effectiveness, this method can be used for routine, real-time determination of methanol in alcoholic solutions.

Efficient conversion of used palm cooking oil into biogasoline over hydrothermally prepared sulfated mesoporous silica loaded with NiMo catalyst

Fossil-based fuels remain a primary global energy source, but their finite and non-renewable nature raises concerns about long-term sustainability. These issues underscore the urgent need for renewable and eco-friendly alternatives such as converting vegetable oil into biofuel. The present work reported biogasoline production from used palm cooking oil catalyzed by sulfated mesoporous silica impregnated with nickel-molybdenum bimetal using the hydrothermal method for both steps. We evaluated the effect of sulfuric acid concentration and metal loading amount on the acidity of the resulting catalysts. Catalysts' performance was assessed through the catalytic cracking and hydrocracking processes with a catalyst-to-feed ratio of 1% at 550°C and an atmospheric pressure. In comparison to mesoporous silica (MS) and sulfated mesoporous silica (SMS-2), along with an increase in acidity, NiMo-impregnated mesoporous silica (NiMo 1/SMS-2) exhibited superior catalytic performance in biogasoline production in the presence of H2 gas, achieving liquid product conversion and gasoline selectivity of 55.9% and 52.37%, respectively. These results are an excellent step for developing biogasoline in a safer process and confirm the capability of mesoporous silica-based catalysts in biofuel production.

STUDY OF THE BEHAVIOR OF ARSENIC IN COPPER ELECTROLYTE

Abstract. In industrial wastewater, arsenic is most often present in the trivalent state. An analysis of existing purification methods shows that in all cases, with a few exceptions, the most complete removal of arsenic is observed from solutions in which it is in the pentavalent state. This is explained by the significantly lower solubility of arsenates of heavy and alkaline earth metals compared to the corresponding arsenites. The chemical oxidation of As(III) in the following systems was studied: As(III)-H2SO4-H2O, As(III)-MeSO4-H2O, As(III)–H2SO4–MeSO4–H2O (where Me is Cu, Ni, Co, Mn, Zn). The influence of temperature, the amount of transition metal ions, the duration of the experiment, and the concentration of sulfuric acid on the degree of transition of As(III) to As(V) was studied. The effect of catalytic oxidation of As(III) in sulfuric acid solutions was discovered. The maximum degree of oxidation of trivalent arsenic (55-60%) is observed when transition metal salts are introduced into an arsenic solution in the presence of a platinum plate. It has been established that the nature of the studied transition metal salts (Cu2+, Ni2+, Co2+, Mn2+, Zn2+), process duration and temperature do not have a significant effect on the degree of As(III) conversion. The results obtained largely explain the predominance of pentavalent forms of arsenic in production solutions of non-ferrous metallurgy. Key words: copper electrolyte, arsenic, transition metals, catalytic role, instant oxidation effect, activated oxygen.

VALORIZATION OF LIGNOCELLULOSIC BIOMASS BY DARK FERMENTATION: DEVELOPMENT OF EFFECTIVE CONDITIONS FOR MOLECULAR HYDROGEN BIOSYNTHESIS

Valorization of lignocellulosic biomass (LB) is important to reduce their environmental impact and reduce the risk to human health. Conventional methods for handling secondary raw materials primarily focus on waste disposal, treating lignocellulosic biomass as waste rather than as a source of organic substances for producing value-added products. As an alternative, processes should be developed to add value to waste, producing value-added products with economic and environmental benefits. In this regard, studies have focused on operating parameters, pretreatment, and microbial fermentation to enhance hydrogen yield during dark fermentation. Upper (4%) and lower (20%) concentrations of distillery grain based substrates for biohydrogen synthesis using wild-type E. coli have been established. Conditions for rational formation of reducing sugars by varying feedstock and acid concentrations in distillery grain based substrates have been established. During the study of the effect of acid-hydrothermal treatment of stillage on the total yield of biohydrogen, it was found that the optimal concentration of sulfuric acid is 1,5%, while 10% of the raw material is used. Under these conditions, the maximum yield of molecular hydrogen was achieved, equal to 116 ±1,0 ml/l using wild-type E. coli.

Complex Protection of Some Steels in Sulfuric Acid Solutions by 1,2,4-Triazole Derivatives.

The corrosion behavior of steels of various grades in sulfuric acid solutions with the addition of nitrogen-containing corrosion inhibitors has been studied. Compounds containing the 1,2,4-triazole moiety effectively protect low-carbon (St3, St20, 08PS), high-strength (70S2KhA), and stainless steels (1Kh18N9T) not only from corrosion but also from the hydrogen penetration into the metals in concentrated sulfuric acid solutions. In some cases, the degree of steel protection from corrosion by these compounds exceeded 99%. The possibility of creating mixed inhibitors for steel protection containing triazole derivatives and KI has been shown. The rate constants for the main steps of cathodic evolution and hydrogen penetration into steel in sulfuric acid solutions have been determined, and the subsurface concentrations of hydrogen in the metals have been calculated. Triazole derivatives were found to act as inhibitors of hydrogen absorption by steel in H2SO4 solution. The degree of protection of steel from hydrogen absorption can reach 97%. It has been shown that triazole derivatives act as complex inhibitors of steel corrosion in sulfuric acid solutions because, along with strong inhibition of metal corrosion, they prevent hydrogen absorption by steel.