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This study focuses on understanding the chemical reactions and results of Kraft lignin transformation through nitric acid treatment and subsequent carbonization. With its rich carbon content, lignin stands out as a promising candidate for the manufacturing of high-value carbon materials. The lignin underwent effective nitration, depolymerization, and oxidation under ambient conditions and at 40 °C, while a slight increase in reaction temperature significantly reduced the reaction time. The molecular weight M w was effectively reduced from 4371 g/mol to 767 g/mol. The acid-treated lignin samples with incorporated nitro groups were further carbonized to create nitrogen-doped carbon structures. The resulting materials show stable nitrogen content (about at 5 wt%) even after carbonization due to the transformation of nitro groups into thermally stable pyridinic moieties, thereby exhibiting enhanced electrocatalytic properties compared to nitrogen-free carbon materials derived from Kraft lignin. The nitric acid-assisted treatment of lignin obviates the need for catalysts, and additional extraction or purification steps for preparing bio-derived carbon precursors, rendering it facile, fast, and cost-efficient., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

This study investigates the formation of atmospheric molecular clusters containing ammonia (NH 3 , A), methylamine (CH 3 NH 2 , MA), or dimethylamine (CH 3 NHCH 3 , DMA) with nitric acid (HNO 3 , NA) using quantum mechanics. The Atmospheric Cluster Dynamic Code (ACDC) was employed to simulate the total evaporation rate, formation rate, and growth pathways of three types of clusters under dry and hydrated conditions. This study evaluates the enhancing potential of A/MA/DMA for NA-based new particle formation (NPF) at parts per trillion (ppt) levels. The results indicate that A/MA/DMA can enhance NA-based NPF at high nitric acid concentrations and low temperatures in the atmosphere. The enhancing potential of MA is weaker than that of DMA but stronger than that of A. Cluster growth predominantly follows the lowest free energy pathways on the acid-base grid, with the formation of initial acid-base dimers (NA)(A), (NA)(MA), and (NA)(DMA) being crucial. Hydration influences the evaporation rate and formation rate of clusters, especially for initial clusters. When the humidity is at 100%, the formation rate for NA-A, NA-MA, and NA-DMA clusters can increase by approximately 10 9 , 10 7 , and 10 4 -fold compared to the corresponding unhydrated clusters, respectively. These results highlight the significance of nitric acid nucleation in NPF events in low-temperature, high-humidity atmospheres, particularly in regions like China with significant automobile exhaust pollution.

The Cu content in discarded printed circuit boards (PCBs) is a crucial aspect, and employing suitable methods for the recovery of Cu holds significance in resource recovery. However, the selective recovery of Cu from an acidic leaching solution containing multiple metals such as Ni, Zn, and Pb poses challenges. L-cys contains the thiol (-SH), the amino (-NH 2 ) and the carboxyl (-COOH) groups, which may complex with metal ions. In particular, the reaction between thiol groups and metal ions makes it possible to recover Cu. In this study, we propose an innovative method using L-cysteine (L-cys) to recover Cu from the acidic leaching solution of discarded PCBs. The effects of Ni 2+ , Zn 2+ , Pb 2+ , Al 3+ , and Fe 3+ irons on the recovery of Cu were studied based on the concentration of these metal ions in PCBs. Adding 120 mL of 2 g/L solution of L-cys to 100 mL of 500 mg/L solution of Cu(NO 3 ) 2 achieved the complete recovery of Cu by forming precipitates. The Ni 2+ , Zn 2+ , Pb 2+ , and Al 3+ ions did not affect the recovery of Cu within the studied metal concentration range in the acidic leaching solution. However, approximately 20% of the Fe 3+ is coprecipitated during the recovery of Cu. This is mainly affected by the amount of colloid formed when copper precipitates in the solution. The interference of Fe 3+ on copper recovery can be effectively reduced by controlling the volume of L-cys to reduce the formation of colloid. Fourier transform infrared and X-ray photoelectron spectroscopy analyses demonstrates the chemical action between the functional groups in L-cys and Cu 2+ . Compared with nickel, zinc and lead ions, copper ions have the strongest binding ability with (-SH), amino (-NH 2 ) and carboxyl (-COOH) groups. This result explains why L-cys can selectively recover copper from leaching solution. This method offers advantages such as fast reaction rates, convenient operating conditions, and enhanced selectivity, which is a promising avenue for the clean and efficient recovery of Cu from discarded PCBs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Carbon fibres (CF) are commonly used as carriers in biofilm-based wastewater treatment. The surface properties of the CF are herein modified using a combination of nitric acid oxidation and urea to optimise the carrier to immobilise bacterial cells. The capacity of the CF carriers to immobilise bacterial cells and activated sludge is evaluated using bacterial cell adhesion and sludge immobilisation tests. The total interaction energy profiles between the CF supports and bacterial cells were calculated according to the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to explain the mechanism by which these modifications enhance this immobilisation capacity. CF-U has a high capacity for immobilising bacterial cells and activated sludge (3.7 g-sludge/g-CF supports) owing to its low total interaction energy. Nitric acid oxidation reduced the diiodomethane contact angle of CF from 55.1° to 38.5°, which reduced the Lifshitz-van der Waals interaction energy, while urea modification further increased the zeta potential of CF from 12.8 mV to -0.7 mV, thereby reducing the electrostatic interaction energy. Experiments and DLVO theory both determined that a combination of nitric acid oxidation and urea modification significantly enhanced the ability of CF to immobilise microorganisms.

Metal ions may act as enzyme cofactors and influence the kinetics of biochemical reactions that may also influence the biological production of therapeutic proteins and quality attributes such as glycosylation. Because sample preparation is a significant step in the reliable analysis of metals, we compared two sample preparation procedures for metal analysis of bioreactor culture media samples by ICP-MS: (i) samples were diluted in 2 % nitric acid (treatment with nitric acid, TNA); and (ii) samples were mixed with equal volume of 5 % nitric acid and closed vessel digestion was performed in a microwave (closed vessel digestion, CVD). In the comparison of extraction efficiencies between TNA and CVD procedures, CVD showed better extraction for Ca and Cu among bulk metals (∼30 %) and for Ni among the trace metals (∼65 %) for the bioreactor broth supernatant samples. For the cell pellet samples, the CVD procedure was found to be better for extraction of Fe (∼65 % more) among bulk metals, Zn (∼20 % more) among minor metals and Co (∼60 % more) and Ni (∼45 % more) among trace metals. Differences between the two procedures were less than 10 % and TNA was better for all other metals quantified from both supernatant samples and cell pellet samples. The current study helps bring more clarity to the methodology on comprehensive metal analysis to monitor and maintain trace metal content for biologics production., Competing Interests: Declaration of competing interest None., (Published by Elsevier Inc.)

Abstract The increasing amount of coal gasification fine slag (CGFS) necessitates its resource utilization. CGFS, mainly composed of porous carbonaceous particles and partially fused spherical or agglomerated ash particles, is an inexpensive and high-quality raw material for preparing adsorbent materials. However, the challenge remains in developing a simple, low-cost, and environmentally friendly method to produce high-performance porous materials from CGFS. In this study, a one-step treatment method using 2 mol/L nitric acid under hydrothermal conditions was proposed for CGFS. The adsorbent material (CGFS-2 M) prepared under a solid–liquid ratio of 2:5 and an initial concentration of 200 mg/L methylene blue (MB) exhibited an equilibrium adsorption capacity as high as 210.20 mg/g. The excellent adsorption performance of CGFS-2 M can be attributed to several factors: acid leaching for mineral removal and pore formation, resulting in a specific surface area and total pore volume 2.2 and 1.6 times that of untreated CGFS, respectively, and an optimized mesoporous pore size distribution favorable for MB adsorption; optimal mineral removal and a well-defined carbon microcrystal structure providing more space for MB adsorption; nitric acid treatment increasing the surface oxygen content and hydrophilicity, enhancing its ability to remove MB. The synergistic effect of pore structure improvement and surface modification indicates a feasible research direction for enhancing the performance of CGFS-based adsorbent materials. These results provide theoretical support for the development of efficient CGFS-based adsorbents.

Nitric acid, an important basic chemical raw material, plays an important role in promoting the development of national economy. However, such liquid hazardous chemicals are easy to cause accidental leakage during production, transportation, storage and use. The high concentration and corrosive toxic gas generated from decomposition shows tremendous harm to the surrounding environment and human life safety. Therefore, how to inhibit the volatilization of nitric acid and effectively control and block the generation of the toxic gas in the first time are the key to deal with the nitric acid leakage accident. Herein, a new method of molecular film obstruction is proposed to inhibit the nitric acid volatilization. The molecular film inhibitor spontaneously spread and form an insoluble molecular film on the gas-liquid interface, changing the state of nitric acid liquid surface and inhibiting the volatilization on the molecular scale. The inhibition rate up to 96% can be achieved below 45 °C within 400 min. Cluster structure simulation and energy barrier calculation is performed to elucidate the inhibition mechanism. Theoretical analysis of energy barrier shows that the specific resistance of the inhibitor significantly increased to 460 s·cm -1 at 45 °C, and the generated energy barrier is about 17,000 kJ·mol -1 , which is much higher than the maximum energy required for nitric acid volatilization of 107.97 kJ·mol -1 . The molecular film obstruction strategy can effectively inhibit the volatilization of nitric acid. This strategy paves the way for preventing the volatilization of liquid hazardous chemicals in accidental leakage treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Background. Promising raw materials for obtaining calcium and calcium nitrate are marble and limestone from the Zarbant deposit, containing CaO above 52.16%. Purpose. Determination of the composition and decomposition coefficient of the Zarbant mine marble with nitric acid. Methodology. The CaO content was determined by the complexometric method with Trilon B, and nitrogen - by the Kjeldahl method. Originality. It was found that the decomposition coefficient of the Zarbant marble components depends on the concentration, temperature, and decomposition time. Optimum conditions for the process of marble decomposition with nitric acid were found. Findings. It was found that an increase in the concentration of nitric acid to 49.21% and an increase in the rate to 100% contribute to an increase in the yield of calcium nitrate to 90%, an increase in temperature and time increases nitrogen losses by 2%; conditions: concentration and acid feed rate - 49.21% and 100%, temperature - 25-30°C, time - 2 hours. [ABSTRACT FROM AUTHOR]

Nitric acid became commonly available in the seventeenth century. Since then, it held the interest of chemists, especially those interested in the art of dyeing. Due to what is now called the xanthoproteic reaction (from Greek xanthós , describing shades of yellow), nitric acid produces a stable yellow colouration in proteinaceous materials, such as wool, silk, and bones. The chemistry of this reaction is well understood today. Less well-known is that it held the interest of dyers in the past. Dyers considered the ability of nitric acid to give a yellow colour to certain substances a solution to giving materials a durable, that is, a lasting, yellow colour. Yellow, indeed, posed a problem in the art of dyeing. Before the discovery of synthetic dyes in the mid-nineteenth century, there were no organic yellow dyes with long-term colour stability. Using historical dyeing manuals and chemistry treatises, combined with our practical engagement with the processes they describe, this paper traces how, between the seventeenth and nineteenth centuries, dyers explored nitric acid while examining the durability of yellow colourations. Based on these explorations into nitric acid, the chemical arts developed theories about the nature of colour, and about the causes for its relative permanence.

With the rapid development of global digital economy and aerospace, the gap between the supply and demand of germanium is expanding, and the establishment of a new process for the deep leaching of germanium from hard zinc slag is imminent. In this paper, on the basis of analyzing the reasons for the low germanium leaching rate from hard zinc slag, a new process of germanium leaching enhanced by HNO3 dissolution of externally wrapped ZnFe2O4 is established, and response surface optimization is carried out. The PbggGe4O7 phase in hard zinc slag is externally wrapped with ZnFe2O4 phase, and the non-reaction between ZnFe2O4 and hydrochloric acid is the main reason for the low leaching rate of germanium from hard zinc slag, so it is necessary to add HNO3 to dissolve the external ZnFe2O4 in leaching, and then use hydrochloric acid to leach the PbGe4O7 containing germanium in the interior. The potential pH diagram of the Pb-Ge-Cl-H2O system was also plotted, indicating that increasing the concentration of chloride ions during hydrochloric acid leaching contributes to the generation of GeCl4 at low acidity. When the hydrochloric acid concentration was 134.65 g/L, the liquid–solid ratio was 6, the theoretical dosage of HNO3 was 0.3, and the leaching time was 236 min, the optimum leaching rate of germanium was 93.72%, which was 23.72% higher than that of germanium leaching from hard zinc slag.

Hydrothermal reactions can convert lignin into carbon dots, and the process often uses acids as additives, but the mechanism of action is not clear. In this study, lignin-based carbon dots were successfully prepared by HNO3-assisted one-pot hydrothermal method. The mechanism of the influence of the acidic environment on the structure and optical properties of lignin-based carbon dots was also investigated by changing the addition amount of HNO3. It was found that the particle size distribution of carbon dots collected was 1-5 nm, and they could emit bright blue fluorescence under violet light irradiation with the highest fluorescence quantum yield of 10.17%. HNO3 acts on the branched chains and ether bonds of alkali lignin, prompting the depolymerization of lignin and re-cross-linking and condensation to form lignin-based carbon dots. With the increase of HNO3 addition, the carbon core of lignin-based carbon dots gradually transformed from amorphous structure to complete graphene-like structure, and the emission wavelength of lignin-based carbon dots shifted from 517 nm to 499 nm, and the fluorescence quantum yield was increased from 2.61% to 10.17% by the effect of integrated N doping, which is of great significance for the analysis of the conformational relationship of lignin-based carbon dots, and for the guidance of the high-efficiency synthesis of lignin-based carbon dots.

Constructing heterojunctions with vacancies has garnered substantial attention in the field of piezo‐photocatalysis. However, the presence of interfacial vacancies can serve as charge‐trapping sites, leading to the localization of electrons and hindering interfacial charge transfer. Herein, dual oxygen vacancies in the NiFe‐layered double hydroxide and Bi2MoO6−x induced interfacial bonds have been designed for the piezo‐photocatalytic N2 oxidation to NO3−. Fortunately, it achieves sensational nitric acid production rates (7.23 mg g−1 h−1) in the absence of cocatalysts and sacrificial agents, which is 6.03 times of pure Bi2MoO6 that under ultrasound and light illumination. Theoretical and experimental results indicate that interfacial bonds act as "charge bridge" and "strain center" to break the carrier local effect and negative effects with piezocatalysis and photocatalysis for promoting exciton dissociation and charge transfer. Moreover, the strong electronic interaction of the interfacial bond induces internal reconstruction under ultrasound for promoting the local polarization and adsorption of N2, which accelerates the fracture of the N≡N bonds and reduces the activation energy of the reaction. The research not only establishes a novel approach for optimizing the combined effects of piezo‐catalysis and photocatalysis, but also achieves equilibrium between the synergistic impacts of vacancies and heterojunctions. [ABSTRACT FROM AUTHOR]

Centrifugal contactors (CCs) are a technology candidate for the development of advanced reprocessing flowsheets. While they offer many advantages, such as process intensification, there are still uncertainties regarding their industrial deployment. The presence of particles in the process streams in particular may present a challenge to both performance and operability. Preliminary studies have been undertaken to evaluate the accumulation of particles in the contactors and the effect upon the extraction behaviour of nitric acid. Aluminium oxide (Al2O3) particles were suspended in the aqueous feed solution during the operation of a three-stage, 40 mm diameter CC cascade. The presence of insoluble solid particles in the aqueous feed, up to 7 g/L, were not observed to affect phase separation and entrainment under the experimental conditions investigated. The particles were centrifuged out of solution and accumulated as a thin cake/bed in the rotors of each stage. This work also illustrates that particles do entrain through the cascade. The predominant effect on the rate of accumulation was particle concentration in the aqueous feed solution, and increasing solids loading was observed to have an impact upon the extraction of nitric acid across the cascade. [ABSTRACT FROM AUTHOR]

In the present work, quinoxaline (0.002 M) as a corrosion inhibitor for copper in 1.5 M HNO3 has been investigated at different temperatures. Weight loss, regression, and density functional theory (DFT) were used in the experimental, mathematical, and quantum chemical studies, respectively. Experimental studies show that the corrosion rate of copper increases with temperature, according to the Arrhenius equation. On the other hand, the percentage of inhibitor efficiency increased as temperature decreased, approaching a maximum value of 91 % at 25 °C. Kinetic studies showed that the corrosion reaction was zero-order. Corrosion rate data was fitted to a second-order mathematical model with a 0.974 correlation coefficient. The effect of inhibitor concentration on the corrosion rate was studied at low and high levels of temperature. The corrosion rate decreases with an increase in an increase in inhibitor concentration. The adsorption on the copper surface was spontaneous and followed the Langmuir adsorption isotherm. The theoretical quantum chemical calculation was used to support the experimental study. These calculations showed that the inhibitor molecules were the donors of electrons, while the metal surface was the acceptor. In addition, Mulliken charge data showed that the negative charges of quinoxaline are mainly concentrated on the nitrogen and carbon atoms. On the other hand, all hydrogen atoms have positive charges. This indicates a lack of hydrogen bond formation with the copper surface. This extensive study not only confirms quinoxaline’s efficacy as a corrosion inhibitor but also advances our knowledge of how it interacts with copper, opening the way to the creation of more focused and effective corrosion inhibitors that follow the rules of molecular design.

Abstract Constructing heterojunctions with vacancies has garnered substantial attention in the field of piezo‐photocatalysis. However, the presence of interfacial vacancies can serve as charge‐trapping sites, leading to the localization of electrons and hindering interfacial charge transfer. Herein, dual oxygen vacancies in the NiFe‐layered double hydroxide and Bi2MoO6−x induced interfacial bonds have been designed for the piezo‐photocatalytic N2 oxidation to NO3−. Fortunately, it achieves sensational nitric acid production rates (7.23 mg g−1 h−1) in the absence of cocatalysts and sacrificial agents, which is 6.03 times of pure Bi2MoO6 that under ultrasound and light illumination. Theoretical and experimental results indicate that interfacial bonds act as “charge bridge” and “strain center” to break the carrier local effect and negative effects with piezocatalysis and photocatalysis for promoting exciton dissociation and charge transfer. Moreover, the strong electronic interaction of the interfacial bond induces internal reconstruction under ultrasound for promoting the local polarization and adsorption of N2, which accelerates the fracture of the N≡N bonds and reduces the activation energy of the reaction. The research not only establishes a novel approach for optimizing the combined effects of piezo‐catalysis and photocatalysis, but also achieves equilibrium between the synergistic impacts of vacancies and heterojunctions.

The nuclear criticality safety issue in spent fuel reprocessing facilities is closely related to the main process and is almost equally important. It is closely related to the design and operation of reprocessing facilities. The requirement of nuclear criticality safety greatly restricts the operational capacity of the spent fuel reprocessing process, thereby affecting the economic efficiency of reprocessing. In the post-processing process, both multiphase uranium-plutonium mixed systems and multi body interaction systems are involved. The system characteristics are complex, and experimental simulation is difficult, which greatly restricts the further improvement of the production and operation capabilities of the pilot plant. However, due to the criticality safety challenges caused by reactivity changes such as the non-uniformity, dynamic complexity, and instability of the solution in the reactor under boiling nitric acid during the dissolution process, it has become a key research topic in various countries. According to the criticality safety problem of nuclear fuel dissolution process, the criticality effect of nitric acid concentration was studied. The criticality experiment data of nuclear fuel dissolution process were obtained by keeping the concentration of nitric acid in the same fuel concentration. Four experiments were conducted with different concentrations of nitric acid. During the experiment, the subcritical extrapolation method, reactivity interpolation method, and stable power method were used to complete the criticality experiment. The experimental results show that with the increase of nitric acid concentration, the relative deviation of the criticality experiment data is 0.068%, and the relative deviation between the criticality experiment results and the theoretical calculated values is 0.39%. The research results show that the reactivity of the system gradually increases as the concentration of nitric acid decreases. Therefore, it is necessary to consider the reactivity changes caused by changes in the criticality safety of the spent fuel dissolution process, and high attention is needed. According to the agreement between the experiment and the theoretical calculation, it is appropriate to use the Monte Carlo code MONK to calculate and analyze the acidity effect of the solid-liquid two-phase solution system, which can be used as a nuclear criticality safety control engineering design process for the solid-liquid two-phase nuclear fuel dissolution system. This series of experiment data can be used for calculation, verification, and safety evaluation of critical analysis under solid-liquid coexistence conditions of nuclear fuel. This paper results provide data support for improving the criticality safety control level of critical post-processing equipment.

The production of nitric acid represents the primary source of nitrous oxide (N2O) emissions. During pilot-scale studies of N2O reduction on a low-temperature catalyst on nitric acid plants, it was observed that increasing the concentration of NH3 resulted in a decrease in the degree of N2O decomposition. This suggested that N2O was formed by the oxidation of NH3. Measurements at different temperatures, conducted after the N2O reduction trials, resulted in the N2O concentration at the inlet equal to the concentration at the outlet, indicating catalyst deactivation. To identify the causes of deactivation, the physicochemical properties of the catalyst were investigated. XRF analysis revealed the presence of sulfur. The results suggest the necessity of removing sulfur from the raw gas before the reduction of N2O on the low-temperature catalyst in practical applications.

This study proposed mixing HNO3 solution with low-lime calcium silicate cement (CSC) to enhance the CO2 capture and mechanical properties after CO2-curing by increasing Ca2+ leaching at the initial stage. To clarify the influences of HNO3 and the reaction mechanisms, various molar concentrations of HNO3 (0, 0.01, 0.05, 0.1, 0.2, 0.5, and 1.0 M) were homogenized with CSC using a liquid-to-solid ratio (L/S) of 0.4 and CO2-cured in a pressurized chamber for 24 h. The impact of HNO3 on the initial reaction kinetics, Ca2+ leaching, phase composition after curing, CO2 fixation capability, and mechanical performance were investigated. The findings revealed that the incorporation of HNO3 had a pronounced influence on the degree of reaction, CO2 fixation, and mechanical performance of CSC pastes. Nevertheless, the excessive incorporation of HNO3 had a notable adverse impact on the reaction.