Search

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.

Half of the world's food production depends on synthetic nitrogen fertilizers. The production of these fertilizers is responsible for 1% of global greenhouse gas emissions. Greentech start-ups like NitroCapt have developed new low-carbon technologies and aim to enter the market within the next few years. The aim of this thesis was to understand the impact of value-based pricing on market entry decisions. Therefore, qualitative interviews with experts and customers were conducted, complemented by secondary data. The results of this case study indicate a strong influence of regulations and customer values. The existing regulations will significantly increase the cost of gray fertilizer due to the taxation of production emissions. The EU has set ambitious targets for green ammonia and fertilizer production by 2030. Supply is unlikely to meet this mandated demand. In addition, customer demand is uncertain today because green products are not widely available. Increasing consumer demand for low-carbon foods and the high potential to reduce the carbon footprint of the product for a small increase in cost can significantly increase the demand for green fertilizers. The imbalance between supply and demand creates the basis to benefit from a green premium on low carbon emissions as an early mover at least until 2030. Low carbon emissions have proven to have a high value. The market prices for grey calcium nitrate fertilizer in the horticultural market are higher compared to the agricultural and industrial nitric acid market. Therefore, it may be attractive to choose niche entry with a value-based price skimming strategy or even penetration pricing if the entrant's cost structure allows it. The application of the six contingencies of entry choices, supplemented by an economic value analysis, proved to be a suitable method for researching value-based pricing. It can therefore serve as a blueprint, especially in the context of Greentech innovation and other hard-to-abate indust

Chemically modified carbon nanotubes are recognized as effective materials for tackling bacterial infections. In this study, pristine multi-walled carbon nanotubes (p-MWCNTs) were functionalized with nitric acid (f-MWCNTs), followed by thermal treatment at 600 °C, and incorporated into a poly(dimethylsiloxane) (PDMS) matrix. The materials’ textural properties were evaluated, and the roughness and morphology of MWCNT/PDMS composites were assessed using optical profilometry and scanning electron microscopy, respectively. The antibiofilm activity of MWCNT/PDMS surfaces was determined by quantifying culturable Escherichia coli and Staphylococcus aureus after 24 h of biofilm formation. Additionally, the antibacterial mechanisms of MWCNT materials were identified by flow cytometry, and the cytotoxicity of MWCNT/PDMS composites was tested against human kidney (HK-2) cells. The results revealed that the antimicrobial activity of MWCNTs incorporated into a PDMS matrix can be efficiently tailored through nitric acid functionalization, and it can be increased by up to 49% in the absence of surface carboxylic groups in f-MWCNT samples heated at 600 °C and the presence of redox activity of carbonyl groups. MWCNT materials changed the membrane permeability of both Gram-negative and Gram-positive bacteria, while they only induced the production of ROS in Gram-positive bacteria. Furthermore, the synthesized composites did not impact HK-2 cell viability, confirming the biocompatibility of MWCNT composites.

Binary palladium alloys with nickel are known to have catalytic activity and are also used as catalyst-trap in the synthesis of nitric acid. High Pd alloys are corrosive resistant in many solutions, including highly alkaline and highly acidic. Although generally not prone to corrosion in low concentrations of mineral acids due to the high content of palladium in it, this alloy is still prone to the dealloying effect under specific conditions. The dealloying process was researched under anodic polarization in 1.0M nitric acid solution. Scanning electronic microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and electrochemical methods were used to study the susceptibility of PdNi5 alloy to dealloying.

Abstract. In this paper, we exploit the first 10-year data record (2008–2017) of nitric acid (HNO3) total columns measured by the IASI-A/MetOp infrared sounder, characterized by an exceptional daily sampling and a good vertical sensitivity in the lower-to-mid stratosphere (around 50 hPa), to monitor the relationship between the temperature decrease and the observed HNO3 loss that occurs each year in the Antarctic stratosphere during the polar night. Since the HNO3 depletion results from the formation of polar stratospheric clouds (PSCs), which trigger the development of the ozone (O3) hole, its continuous monitoring is of high importance. We verify here, from the 10-year time evolution of HNO3 together with temperature (taken from reanalysis at 50 hPa), the recurrence of specific regimes in the annual cycle of IASI HNO3 and identify (for each year) the day and the 50 hPa temperature (“drop temperature”) corresponding to the onset of strong HNO3 depletion in the Antarctic winter. Although the measured HNO3 total column does not allow for the uptake of HNO3 by different types of PSC particles along the vertical profile to be differentiated, an average drop temperature of 194.2 ± 3.8 K, close to the nitric acid trihydrate (NAT) existence threshold (∼ 195 K at 50 hPa), is found in the region of potential vorticity lower than −10 × 10−5 Km2kg-1s-1 (similar to the 70–90∘ S equivalent latitude region during winter). The spatial distribution and interannual variability of the drop temperature are investigated and discussed. This paper highlights the capability of the IASI sounder to monitor the evolution of polar stratospheric HNO3, a key player in the processes involved in the depletion of stratospheric O3.

This paper describes the nitric acid dissolution process of natural minerals such as ten-nantite, chalcopyrite and sphalerite, with the addition of Fe (III) ions and FeS2. These minerals are typical for the ores of the Ural deposits. The effect of temperature, nitric acid concentration, time, additions of Fe (III) ions and FeS2 was studied. The highest dissolution degree of sulfide minerals (more than 90%) was observed at a nitric acid concentration of 6 mol/dm3, an experiment time of 60 min, a temperature of 80 °C, a concentration of Fe (III) ions of 16.5 g/dm3, and an addition of FeS2 to the total mass minerals at 1.2:1 ratio. The most significant factors in the break-down of minerals were the nitric acid concentration, the concentration of Fe (III) ions and the amount of FeS2. Simultaneous addition of Fe (III) ions and FeS2 had the greatest effect on the leaching process. It was also estab-lished that FeS2 can be an alternative catalytic surface for copper sulfide minerals during nitric acid leaching. This helps to reduce the influence of the passivation layer of elemental sulfur due to the galvanic linkage formed between the minerals, which was confirmed by SEM-EDX. © 2022 by the author. Licensee MDPI, Basel, Switzerland.

Refractory sulphidic ore with gold captured in pyrite has motivated researchers to find efficient means to break down pyrite to make gold accessible and, ultimately, improve gold extraction. Thus, the dissolution of pyrite was investigated to understand the mechanism and find the corresponding kinetics in a nitric acid solution. To carry this out, the temperature (25 to 85 °C), nitric acid concentration (1 to 4 M), the particle size of pyrite from 53 to 212 µm, and different stirring speeds were examined to observe their effect on pyrite dissolution. An increase in temperature and nitric acid concentration were influential parameters to obtaining a substantial improvement in pyrite dissolution (95% Fe extraction achieved). The new shrinking core equation (1/3ln (1 − X) + [(1 − X)−1/3 − 1)]) = kt) fit the measured rates of dissolution well. Thus, the mixed–controlled kinetics model describing the interfacial transfer and diffusion governed the reaction kinetics of pyrite. The activation energies (Ea) were 145.2 kJ/mol at 25–45 °C and 44.3 kJ/mol at higher temperatures (55–85 °C). A semiempirical expression describing the reaction of pyrite dissolution under the conditions studied was proposed: 1/3ln(1 − X) + [(1 − X)−1/3 − 1)] = 88.3 [HNO3]2.6 r0−1.3 e−44280/RT t. The solid residue was analysed using SEM, XRD, and Raman spectrometry, which all identified sulphur formation as the pyrite dissolved. Interestingly, two sulphur species, i.e., S8 and S6, formed during the dissolution process, which were detected using XRD Rietveld refinement.

Numerous electronic devices are put out of use every day, and most of them have printed circuit boards (PCBs) that are lased and imbued with various precious and valuable metals in abundant amounts. This makes PCB an unexploited resource of the future from whom many metals such as Cu, Zn, Sn, Al, Li, Co, Nd, Pd, Pt, and Ba can be extracted. Since leaching plastic polymers can lead to the vaporization of toxic fumes, to avoid this the PCB are pyrolyzed. The PCB is crushed and the pyrolyzed product is a powder that can easily be separated into metallic and nonmetalic fractions. The aim of this work is to investigate the influence of ultrasound sonification on the nitric acid leaching of pyrolyzed printed circuit board (PPCB) powder. The impact of ultrasound sonification had a positive effect on the leaching degree for all investigated metals except for Cobalt. The biggest difference in leaching degree was for Lithium while the smallest was for platinum. Because of the complexity of the PPCB powder system overall, the measurement of oxidation-reduction potential (ORP) didn’t yield any insight into the leaching mechanism since the measured values mainly followed the expected trend due to nitric acid degradation.

Bimetallic systems in catalysts could lead to enhanced catalysis resulting in milder reaction conditions and higher turnover rate. The monometallic Nickel on Silica oxide catalysts is often used for hydrogenation reactions, but has limited activity at low temperature. Adding a noble metal in the form of Palladium could enhance the catalyst leading to a bimetallic alloy favorable to certain hydrogenation reactions such as CO2 methanation. Yet, addition of Palladium does not result directly into an improved bimetallic system over the monometallic Nickel catalyst as most of the Palladium in monometallic system is on the outside of the support caused by large sintering. Here we show that recrystallization of the Palladium nitrate source, containing Palladium oxide particles, by using fuming nitric acid as a recrystallization agent leads to enhanced stability of the precursor solution. During synthesis of Palladium catalysts different Palladium nitrate sources were used containing large differences in purity. As a result, the optimal precursor conditions leading to the most active and stable catalyst were not affected by the acidity of the solution but by the fast sintering of Palladium (oxide) particles. These results show that recrystallizing Palladium nitrate sources by fuming nitric acid and vacuum evaporation leads to a general form of Palladium nitrate consisting of little to no Palladium oxide. By repeating the recrystallization with fuming nitric acid ultimately could lead to pure Palladium nitrate sources and enhanced stability of precursor conditions showing no sign of particle formation. Most of the Palladium metal can then enter the support leading to Nickel-Palladium alloying and optimal ratio and weight percentage of metal can be characterized improving the catalyst performance making large CO2 emissions useful for reusage.

A laboratory-scale procedure was developed to obtain lanthanum oxide from spent fluid catalytic cracking catalyst, commonly used in the heavy crude oil cracking process. Two different solids, consisting mainly of silica, alumina, and a certain amount of rare earth elements, were leached under several conditions to recover the rare earths. Nitric acid leaching lead to the highest recovery of lanthanum, reaching a recovery percentage greater than 95% when a 1.5 M concentration was used. Subsequently, liquid phases were subjected to a liquid–liquid extraction process using Cyanex 923 diluted in Solvesso 100, and the lanthanum was quantitatively extracted. Lanthanum was also quantitatively stripped using oxalic acid to obtain the corresponding lanthanum oxalates, as revealed by X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier transform infrared (FTIR) techniques. After thermal treatment at 1200C for 2 h, these solids yielded lanthanum oxide.

At present, the processing of refractory gold–arsenic sulphide concentrates is becoming more relevant due to the depletion of rich crude ore reserves. In the process of the nitric acid leaching of arsenic sulphide minerals, solutions are formed containing 20–30 g/L of arsenic (III). Since market demand for arsenic compounds is limited, such solutions are traditionally converted into poorly soluble compounds. This paper describes the investigation of precipitating arsenic sulphide from nitric acid leaching solutions of refractory sulphide raw materials of nonferrous metals containing iron (III) ions using sodium hydrosulphide with a molar ratio of NaHS/As = 2.4–2.6, which is typical for pure model solutions without oxidants. The work studied the effect of temperature, the pH of the solution and the consumption of NaHS and seed crystal on this process. The highest degree of precipitation of arsenic (III) sulphide (95–99%) from nitric acid leaching solutions containing iron (III) ions without seed occurs with a pH from 1.8 to 2.0 and a NaHS/As molar ratio of 2.8. The introduction of seed crystal significantly improves the precipitation of arsenic (III) sulphide. An increase in seed crystal consumption from 0 to 34 g/L in solution promotes an increase in the degree of transition of arsenic to sediment from 36.2 to 98.1% at pH = 1. According to SEM/EDS and XRF sediment data, from the results of experiments on the effect of As2S3 seed crystal consumption, acidity and molar ratio of NaHS/As on the precipitation of arsenic (III) sulphide and the Fetotal/Fe2+ ratio in the final solution, it can be concluded that the addition of a seed accelerates the crystallisation of arsenic (III) sulphide by increasing the number of crystallisation centres; as a result, the deposition rate of As2S3 becomes higher. Since the oxidation rate of sulphide ions to elemental sulphur by iron (III) ions does not change significantly, the molar ratio of NaHS/As can be reduced to 2.25 to obtain a pr

Nitric acid is manufactured by oxidizing ammonia where the ammonia comes from an energy demanding and non-eco-friendly, Haber-Bosch process. Electrochemical oxidation of N2 to nitric acid using renewable electricity could be a promising alternative to bypass the ammonia route. In this work, we discuss the plausible reaction mechanisms of electrochemical N2 oxidation (N2OR) at the molecular level and its competition with the parasitic oxygen evolution reaction (OER). We suggest the design strategies for N2 oxidation electro-catalysts by first comparing the performance of two catalysts - TiO2(110) (poor OER catalyst) and IrO2(110) (good OER catalyst), towards dinitrogen oxidation and then establish trends/scaling relations to correlate OER and N2OR activities. The challenges associated with electrochemical N2OR are highlighted.

Formaldehyde is a recalcitrant pollutant, which is difficult to remove from wastewater using conventional and advanced treatments. The objective of this research was to remove the organic matter from formaldehyde from an industrial wastewater, achieving its total mineralization and allowing the reuse of the water. The treatment was based on the reaction of formaldehyde with nitric acid, which was first studied and modelled with synthetic waters. Results show that it was possible to almost completely mineralize the formaldehyde (>95% TOC removal) at the best conditions studied (1.72 M of nitric acid and 85 °C of temperature). The addition of NaNO2 accelerated this reaction; however, after 2 h of reaction time, its effect was negligible at the maximum concentration of HNO3 studied. The results obtained with industrial wastewater fit well with the model. It is concluded that formaldehyde in actual wastewaters can be successfully removed through direct mineralization with nitric acid, under selected conditions., Ministerio de Ciencia e Innovación (MICIIN), Comunidad de Madrid, Depto. de Ingeniería Química y de Materiales, Fac. de Ciencias Químicas, TRUE, pub

Marble-cutting tools are commonly produced by hot-pressing techniques or cold-pressing followed by sintering. Cobalt in pure metallic form or alloy form, e.g., Fe-Co, Fe-Cu-Co and Sn-Co, is used as the main component of the metallic binder of most diamond-bearing marble-cutting segments. Extraction of cobalt, copper and silver from scrap saw-blade segments using nitric acid solutions (0.1–0.4 M, 20–60 degrees C) were investigated using response surface methodology. Extraction of cobalt and iron was more extensive than copper and silver, i.e., 35.7–96.2% Co and 72.6–100% Fe versus 8.50–35.4% Cu and 8.11–22.5% Ag. Statistical analysis of the experimental data has shown that increasing the acid concentration or temperature enhances the rate and extent of leaching of metals. Under suitable conditions, almost complete leaching of cobalt (99.9%), as well as high extractions of copper (95.9%) and silver (94.9%), were achieved. The activation energy, calculated to be 40.3 kJ/mol, indicates that nitric acid leaching of these metals occurs as a chemically controlled reaction. These findings have demonstrated that nitric acid as an effective oxidant/leaching agent could be suitably used for the extraction of cobalt, copper and silver from scrap segments., Marble-cutting tools are commonly produced by hot-pressing techniques or cold-pressing followed by sintering. Cobalt in pure metallic form or alloy form, e.g., Fe-Co, Fe-Cu-Co and Sn-Co, is used as the main component of the metallic binder of most diamond-bearing marble-cutting segments. Extraction of cobalt, copper and silver from scrap saw-blade segments using nitric acid solutions (0.1–0.4 M, 20–60 degrees C) were investigated using response surface methodology. Extraction of cobalt and iron was more extensive than copper and silver, i.e., 35.7–96.2% Co and 72.6–100% Fe versus 8.50–35.4% Cu and 8.11–22.5% Ag. Statistical analysis of the experimental data has shown that increasing the acid concentration or temperature enhances the rate and extent of leaching of metals. Under suitable conditions, almost complete leaching of cobalt (99.9%), as well as high extractions of copper (95.9%) and silver (94.9%), were achieved. The activation energy, calculated to be 40.3 kJ/mol, indicates that nitric acid leaching of these metals occurs as a chemically controlled reaction. These findings have demonstrated that nitric acid as an effective oxidant/leaching agent could be suitably used for the extraction of cobalt, copper and silver from scrap segments.

A practical approach was introduced to study the inclusion mechanism of chlorine in high purity copper electrorefining from nitric acid system via cyclic voltammetry (CV) combined with electrodeposition experiments. The CV curves display an obvious reduction peak of CuCl intermediate, which can provide an insight into the electrochemical behaviour of this inclusion. Experimental results show that the increase of HNO3 concentration is favourable to reducing the quantity of chlorine inclusion although there is a slight decline in cathodic current efficiency. The optimum conditions for copper electrorefining in nitric acid system are HNO3 concentration in solution of 1−2 mol/l, moderate temperature of ca. 35 degrees C with current density not exceeding 25 mA/cm2. Based on the theoretical studies, an optimised copper electrorefining experiment was designed to simulate the industrial electrolysis, by which high purity copper can be obtained with chlorine inclusion less than 10 microg/g and current efficiency higher than 90%. (Authors.), A practical approach was introduced to study the inclusion mechanism of chlorine in high purity copper electrorefining from nitric acid system via cyclic voltammetry (CV) combined with electrodeposition experiments. The CV curves display an obvious reduction peak of CuCl intermediate, which can provide an insight into the electrochemical behaviour of this inclusion. Experimental results show that the increase of HNO3 concentration is favourable to reducing the quantity of chlorine inclusion although there is a slight decline in cathodic current efficiency. The optimum conditions for copper electrorefining in nitric acid system are HNO3 concentration in solution of 1−2 mol/l, moderate temperature of ca. 35 degrees C with current density not exceeding 25 mA/cm2. Based on the theoretical studies, an optimised copper electrorefining experiment was designed to simulate the industrial electrolysis, by which high purity copper can be obtained with chlorine inclusion less than 10 microg/g and current efficiency higher than 90%. (Authors.)

Fundamental aspects related to the analysis of nitric acid solutions by inductively coupled plasma mass spectrometry have been critically revisited in order to provide new insights into the possible sources of non-spectroscopic matrix effects and their correction by internal standardization. For elements having first ionization potential (IP) lower than 7.5 eV, the increase in the signal due to nitric acid was ascribed to a delay in the ionization process, which resulted in a reduction of the ion lateral diffusion in the plasma. In contrast, for non-easily ionisable elements, signal depression was correlated with their IP value and attributed to the cooling effect due to the energy required for nitric acid dissociation. Moreover, the atomic mass did not show any significant effect, thus precluding the application of the widely accepted criterion of choice of internal standards based on matching of masses. The extent and sign of the acid effect also depended on the applied operating conditions. For elements with low IP (e.g. Co, Cs, In, Li, Pb, Y), nitric acid caused signal enhancement at high RF power and nebulizer gas flow rate values (i.e., plasma robust conditions) and signal depression under non-robust conditions. For elements with high IP (e.g. As, Be, Cd and Sb), the decreasing acid effect became stronger with increasing the nebulizer gas flow rate and decreasing the RF power. The acid effect was also influenced by the ion lens voltage, that significantly interacted with the RF power effect. Finally, a procedure for the selection of optimal internal standards by principal component analysis has been successfully applied for the correction of the nitric acid effect.

The kinetics of the process of decomposition of dolomite by nitric acid was studied depending on the concentration and temperature. The main kinetic parameters of the decomposition process are established and the equations for the dependence of the foam expansion constant on the acid feed rate are derived.

A cost-effective and simple hydrometallurgy procedure for recycling the diamond core drilling crowns by nitric acid leaching, followed by the sodium hydroxide leaching, has been developed. The effect of temperature, nitric acid/sodium hydroxide concentration, leaching time and stirring rate were studied. For the acid leaching process the optimal values for parameters were 60 degrees C, 1.0 M HNO3, 2.5 h, and 800 rpm. It has been noted that the key factors in the alkaline leaching process were temperature and NaOH concentration. For the alkaline leaching, the optimal parameters were 100 degrees C, 40% concentration of NaOH solution, and leaching time of 4 h. Identification and characterisation of products in all technological processes were performed by X-Ray Diffraction (XRD), scanning electron microscope using energy-dispersive X-ray spectroscopy (SEM-EDS), and laser desorption ionisation mass spectrometry (LDI-MS). The analysis of solutions in all phases was performed by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The use of LDI-MS as a new approach to identify the products after phases in the recycling process was an important part of the study, and the results were consistent with the XRD analysis. The total tungsten recovery was over 95.6%, with a high purity of the obtained tungsten trioxide.

A list of authors and their affiliations appears at the end of the paper New-particle formation is a major contributor to urban smog(1,2), but how it occurs in cities is often puzzling(3). If the growth rates of urban particles are similar to those found in cleaner environments (1-10 nanometres per hour), then existing understanding suggests that new urban particles should be rapidly scavenged by the high concentration of pre-existing particles. Here we show, through experiments performed under atmospheric conditions in the CLOUD chamber at CERN, that below about +5 degrees Celsius, nitric acid and ammonia vapours can condense onto freshly nucleated particles as small as a few nanometres in diameter. Moreover, when it is cold enough (below -15 degrees Celsius), nitric acid and ammonia can nucleate directly through an acid-base stabilization mechanism to form ammonium nitrate particles. Given that these vapours are often one thousand times more abundant than sulfuric acid, the resulting particle growth rates can be extremely high, reaching well above 100 nanometres per hour. However, these high growth rates require the gas-particle ammonium nitrate system to be out of equilibrium in order to sustain gas-phase supersaturations. In view of the strong temperature dependence that we measure for the gas-phase supersaturations, we expect such transient conditions to occur in inhomogeneous urban settings, especially in wintertime, driven by vertical mixing and by strong local sources such as traffic. Even though rapid growth from nitric acid and ammonia condensation may last for only a few minutes, it is nonetheless fast enough to shepherd freshly nucleated particles through the smallest size range where they are most vulnerable to scavenging loss, thus greatly increasing their survival probability. We also expect nitric acid and ammonia nucleation and rapid growth to be important in the relatively clean and cold upper free troposphere, where ammonia can be convected from t

Simple hydroxamic acids such as acetohydroxamic acid (AHA) have the ability to strip Pu(IV) and Np(IV) from tri-butyl phosphate into nitric acid by forming strong complexes with these ions. AHA has thus been identified as a suitable reagent for the control of Pu and Np in advanced separation processes for nuclear fuel reprocessing, such as the Advanced PUREX (Plutonium URanium EXtraction) and the Grouped ActiNide Extraction (GANEX) recycle processes. It is known that both free and complexed AHA undergo an acid catalysed hydrolysis reaction at low pH to form hydroxylamine (NH2OH) and acetic acid (CH3COOH), but the kinetics of this process is not fully understood in these systems. In this work, we have used Fe(III) as a non-active analogue for Pu(IV) and Np(IV) to investigate the hydrolysis kinetics of both free and complexed AHA by utilizing ion chromatography to measure the ingrowth of the acetate ion over time. In contrast to previous studies, our results show that the rate of AHA hydrolysis is inhibited in the presence of Fe(III). From our data we obtain an Arrhenius factor (A) of 1.25 x 10 11 dm 3.mol -1.s -1 and 3.71 x 10 18 dm 3.mol -1.s -1, and an activation energy (Ea) of 89.0 kJ.mol -1 and 137.4 kJ.mol -1 for the hydrolysis of the free and complexed AHA respectively.

Increasingly stringent environmental regulations in different sectors of industry, especially the aeronautical sector, suggest the need for more investigations regarding the effect of environmentally friendly corrosion protective processes. Passivation is a finishing process that makes stainless steels more rust resistant, removing free iron from the steel surface resulting from machining operations. This results in the formation of a protective oxide layer that is less likely to react with the environment and cause corrosion. The most commonly used passivating agent is nitric acid. However, it is know that high levels of toxicity can be generated by using this agent. In this work, a study has been carried out into the electrochemical behavior of 15-5PH (precipitation hardening) and 17-4PH stainless steels passivated with (a) citric and (b) nitric acid solutions for 60 and 90 min at 49 °C, and subsequently exposed to an environment with chlorides. Two electrochemical techniques were used: electrochemical noise (EN) and potentiodynamic polarization curves (PPC) according to ASTM G199-09 and ASTM G5-13, respectively. The results obtained indicated that, for both types of steel, the passive layer formed in citric acid as passivating solution had very similar characteristics to that formed with nitric acid. Furthermore, after exposure to the chloride-containing solution and according with the localization index (LI) values obtained, the stainless steels passivated in citric acid showed a mixed type of corrosion, whereas the steels passivated in nitric acid showed localized corrosion. Overall, the results of the Rn values derived show very low and similar corrosion rates for the stainless steels passivated with both citric and nitric acid solutions.

In the refining and petrochemical industrial sector, large amounts of energy are used, so using the concept of exergy allows a rational use of this resource. In the different exergy and exergoeconomics studies applied in petrochemical plants, parameters of interest have been determined to evaluate the thermal efficiency, the potential for process improvement, the irreversibilities produced by the interaction between the components of the system and the operation of each one, and the energy costs associated with each of these irreversibilities. This paper presents an advanced exergy analysis and an exergy-economic analysis applied to a nitric acid production plant with an installed capacity of 350 metric tons per day, whose operating principle is based on the Ostwald method, and both the behavior of endogenous exergy destruction and the behavior of exogenous, avoidable and unavoidable exergy destruction are studied, exogenous, avoidable and unavoidable exergy destruction and the associated exergy costs in each of the heat transfer equipment and reactive equipment that make up the plant, about the cooling temperature in the intermediate stages of the compression train are studied using a mathematical model. The chemical reactions involved in the production process are the points of interest in the research of this work. Some of the results show that 54 % of the total exergy destruction can be recovered by intervening in the components. On the other hand, in the Catalytic Converter (CONV), it is convenient to consider the investment costs to reduce the exergy destruction costs. Similarly, in the Tail Gas Heater (TGH), it is beneficial to reduce the total investment to improve the process economics. On the other hand, the cost of exergy destruction of the plant resulted in 770.77 USD/h. In addition, it could be determined that the interactions between the components significantly affect the investment costs

© 2020, Chinese Lasers Press. All right reserved. In this study, the high-resolution Fourier transform infrared spectroscopy (FTIR) is used to detect the concentrations of nitric acid (HNO3) in the atmosphere above the Hefei site. The vertical profiles and total columns of HNO3 are retrieved from the mid-infrared solar absorption spectra using the optimal estimation method. The vertical profiles and time series of the total columns of atmospheric HNO3 are obtained over the entire year of 2017. Further, the characteristics of the seasonal variation of HNO3, sensitivity altitude of concentration detection, averaging kernels of retrieved profiles, and degrees of freedom are analyzed. The vertical profiles of atmospheric HNO3 in different seasons denote that the HNO3 concentrations are higher at an altitude of 2030 km in the stratosphere and that they are lower in the troposphere. Furthermore, the total columns of HNO3 exhibit obvious seasonal variations, with a maximum in spring and minimum in winter. The amplitude of the seasonal variations is 9.82×1015 molecule/cm2. The data products obtained from the Aura MLS satellite are selected for performing comparison with the ground-based data to validate the measurements of the ground-based FTIR using independent data. The comparison results denote that the ground-based remote sensing and satellite observations display a consistent seasonal HNO3 variability. The ground-based data exhibits a good agreement with the satellite data with a high correlation coefficient of 0.83 even though the partial columns of the satellite data are lower than the corresponding ground-based total columns. The observation results indicate the reliability and accuracy of the ground-based FTIR for observing the temporal and spatial distributions of the atmospheric HNO3.

Esfordi phosphate concentrate (Yazd Province, Iran) contains 13.1% P, 34.6% Ca, and 1.09% rare-earth elements (REEs), being one of the most important sources of REEs in Iran. REEs can be extracted from phosphate concentrates as a by-product of phosphoric acid production processes. In this work, nitric acid was used for leaching of REEs and phosphate from Esfordi phosphate concentrate, and the effects of the acid concentration (35–65 wt.%), leaching time (30–90 min) and temperature (24–90 degrees C) were investigated. Due to the difficulty of calcium separation from REEs in nitrate-phosphate solutions, the possibility of selective leaching of calcium and phosphate from REEs was examined. At acid concentration of 35%, temperature of 60 degrees C, and leaching time of 70 min, most of the calcium, more than 80% of the phosphate, and less than 10% of the REEs were dissolved. Accordingly, 90.7% of the REEs remained in the residue and their grade was increased from 1% to 4% in the nitric acid leaching residue. This concentrated residue of REEs could be an appropriate feed for subsequent processes, including acid baking. (Authors.), Esfordi phosphate concentrate (Yazd Province, Iran) contains 13.1% P, 34.6% Ca, and 1.09% rare-earth elements (REEs), being one of the most important sources of REEs in Iran. REEs can be extracted from phosphate concentrates as a by-product of phosphoric acid production processes. In this work, nitric acid was used for leaching of REEs and phosphate from Esfordi phosphate concentrate, and the effects of the acid concentration (35–65 wt.%), leaching time (30–90 min) and temperature (24–90 degrees C) were investigated. Due to the difficulty of calcium separation from REEs in nitrate-phosphate solutions, the possibility of selective leaching of calcium and phosphate from REEs was examined. At acid concentration of 35%, temperature of 60 degrees C, and leaching time of 70 min, most of the calcium, more than 80% of the phosphate, and less than 10% of the REEs were dissolved. Accordingly, 90.7% of the REEs remained in the residue and their grade was increased from 1% to 4% in the nitric acid leaching residue. This concentrated residue of REEs could be an appropriate feed for subsequent processes, including acid baking. (Authors.)

The long-term carrying capacity for biomass production is highly dependent on available soil resources. A soil test method for potential nutrient release capability was applied to 23 Nordic and Baltic forest soil profiles. The soils had coarse (10), medium (12) and fine (1) soil texture and most were podsolising. Extraction with dilute (0.1 M, 1:50 sample:solution ratio) nitric acid for 2 h was followed by 48 h and 168 h of extraction in soil samples from pedogenetic horizons. Dilute nitric acid solution was replaced after each step and release of mineral nutrient elements in solution was determined. C-horizon nutrient release (µmol g−1 fine earth, 0–218 h) was negatively correlated with mean annual temperature (MAT 0.5–8.5 °C) and for potassium (K) also mean annual precipitation (MAP 523–1440 mm y−1) suggesting a gradient in the mineralogy of the parent material that sediment transports during Pleistocene glaciations have not distorted. In B-horizons of sandy parent materials with felsic mineralogy cumulative nutrient release was positively correlated with pH and with Al and Fe release suggesting accumulation and stabilisation of nutrients in pedogenic products. E-horizons had less nutrient release capability than C-horizons, indicating a more weathered state of E-horizon parent material. Soil formation due to mineral dissolution and leaching of base cations and the gradient in parent material origin and weathering state both affected the observed pattern of nutrient release. On soils with very low mineral P resources (e.g. <250 kg P ha−1 to 50 cm) by repeated dilute acid extraction, harvest of nutrient rich biomass will not be sustainable. However, it can't be concluded that sites with high P availability by 0.1 M HNO3 can support an intensive harvest without compensation of P (and Ca) by fertilisation. Due to buffering of removed base cations in B-horizons, nutrient export with biomass may not be traceable as pH d

Mineral dust is amongst the largest contributors to the global aerosol mass load and dominates climate effects over large areas of the Earth. Dust undergoes heterogeneous chemical reactions during transport that increase its hygroscopicity, while altering its optical properties, and the associated radiative forcing. The rates of heterogeneous chemical reactions on the dust surface that form coatings of sulfate, nitrate, chloride, or organics depend strongly on the dust mineralogical composition. For example, the uptake of sulfur dioxide by calcite exceeds by at least an order of magnitude uptake by quartz, feldspar and hematite. Dust composition also affects the partitioning of semi-volatile inorganic compounds, altering their burden and radiative forcing.

Waste cooking oil is a waste of frying oil that is containing high free fatty acids (% FFA). The waste could be made to be useful as biodiesel and triacetin. Biodiesel was produced by addition of 4 % (oil weight) activated carbon with stirring for 1hour at 90-100 oC then transesterification of waste cooking oil. The results showed the yield of the biodiesel was 95.28 % with flash point 179oC, water content 0.13 %, acid value 0.59, total glycerol 0.03 %, and the by-product glycerol 10.05 % (oil weight). Triacetin was synthesized by esterification of the glycerol with acetic acid with mol ratio 1 : 7 at 120oC used nitric acid catalyst (5 % glycerol weight). The results showed that the conversion of acetic acid was low, 24.05 %. That showed nitric acid could be a good catalyst in the esterification of triacetin., Minyak jelantah sebagai limbah dari minyak bekas penggorengan mengandung kadar asam lemak bebas yang tinggi. Upaya pemanfaatan limbah minyak jelantah adalah dengan mengubahnya menjadi biodiesel dan triasetin. Pembuatan biodiesel dilakukan dengan penambahan karbon aktif sebanyak 4 % berat minyak dan pengadukan selama 1 jam pada suhu 90-100 oC, dilanjutkan dengan proses transesterifikasi. Proses tersebut mampu mengubah minyak jelantah menjadi biodiesel sebesar 95,28 % berat minyak, dengan titik nyala 179 oC, kadar air 0,13 %, bilangan asam 0,59, gliserol total 0,03 % dan gliserol hasil samping sebesar 10,05 % berat minyak. Triasetin disintesis dengan cara esterifikasi gliserol hasil samping pembuatan biodiesel dengan asam asetat dengan rasio mol 1 : 7 pada suhu 120 oC menggunakan katalis asam nitrat 5 % berat gliserol. Esterifikasi triasetin menunjukkan % konversi asam asetat yang rendah, yaitu sebesar 24,05 %. Hal ini berarti asam nitrat tidak baik digunakan sebagai katalis dalam proses esterifikasi triasetin.

The surfaces of ice crystals near the melting point are covered with thin liquid water layers, called quasi-liquid layers (QLLs), which play crucial roles in various chemical reactions in nature. So far, there have been many spectroscopic studies of such chemical reactions on ice surfaces, however, revealing the effects of atmospheric gases on ice surfaces remains an experimental challenge. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the ice basal faces by advanced optical microscopy under partial pressure of HNO3 (similar to 10(-4) Pa), relevant to those found in the atmosphere. We found that droplets (HNO3-QLLs) appeared on ice surfaces at temperatures ranging from -0.9 to -0.2 degrees C with an increase in temperature, and that they disappeared at temperatures ranging from -0.6 to -1.3 degrees C with decreasing temperature. We also found that the size of the HNO3-QLLs decreased immediately after we started reducing the temperature. From the changes in size and the liquid-solid phase diagram of the HNO3-H2O binary system, we concluded that the HNO3-QLLs did not consist of pure water, but rather aqueous HNO3 solutions, and that the temperature and HNO3 concentration of the HNO3-QLLs also coincided with those along a liquidus line.

The surfaces of ice crystals near the melting point are covered with thin liquid water layers, called quasi-liquid layers (QLLs), which play crucial roles in various chemical reactions in nature. So far, there have been many spectroscopic studies of such chemical reactions on ice surfaces, however, revealing the effects of atmospheric gases on ice surfaces remains an experimental challenge. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the ice basal faces by advanced optical microscopy under partial pressure of HNO3 (similar to 10(-4) Pa), relevant to those found in the atmosphere. We found that droplets (HNO3-QLLs) appeared on ice surfaces at temperatures ranging from -0.9 to -0.2 degrees C with an increase in temperature, and that they disappeared at temperatures ranging from -0.6 to -1.3 degrees C with decreasing temperature. We also found that the size of the HNO3-QLLs decreased immediately after we started reducing the temperature. From the changes in size and the liquid-solid phase diagram of the HNO3-H2O binary system, we concluded that the HNO3-QLLs did not consist of pure water, but rather aqueous HNO3 solutions, and that the temperature and HNO3 concentration of the HNO3-QLLs also coincided with those along a liquidus line.

The major limitation of carbon nanotubes (CNTs) is their poor solubility in the common solvents. Solving the solubility issue of CNTs is comprehended either by functionalizing the CNTs or using a dispersity agent. Agents such as ionic surfactant dramatically alter the suspension conductivity causing undesirable thermal flow in dielectrophoresis (DEP) mediums. In this study, the lack of CNTs solubility in common solvents was resolved by functionalizing multi-wall carbon nanotubes (MWCNTs) using a mild regulated procedure. The mild treatment was used to maintain the electrical conductivity of MWCNTs, since its essential for their dielectrophoretic response. Fourier-transform infrared (FTIR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy were used to investigate the treatment quality. The ability of different solvents to dissolve MWCNT agglomerates after treatment was analyzed using ultraviolet-visible (UV-Vis) spectroscopy and dynamic light scattering (DLS) analysis. The characterization results indicate that the treated MWCNTs by the presented procedure contain hydroxylic and carboxylic functional groups and showed strong solubility in water, dimethylformamide (DMF) and acetone. This study provides a better solution to improve the processability of MWCNTs in common solvents without degrading their electrical conductivity.

This research is a preliminary study of which purpose is to find some information about corrosion behavior of brass casted product in nitric acid. The corrosion rate test was conducted by polarization and Electrochemical Impedance Spectroscopy (EIS). This study was run with the variation of nitric acid of 0,5; 1; 1,5; 2 M. Optical Microscope (OM) were used to explain and to confirm polarization and EIS result. A mechanism for the reactions taking place at the electrode/electrolyte interface was explained.

The catalytic activity of a series of FeOx/Al2O3 prepared under various conditions was evaluated for high temperature decomposition of N2O (HT-deN(2)O) in a complex gas mixture produced by oxidation of ammonia. Thus the relevant step in the industrial nitric acid production process was simulated. The catalyst stability during long-term exposure (12 days) to reaction conditions relevant to HT-deN(2)O was studied. Both fresh and aged FeOx/Al2O3 exhibited more than 90% conversion of N2O in the 750-900 degrees C temperature range. Structural analysis showed that the prepared FeOx/Al2O3 catalysts contained various proportions of , and alumina phases and up to four individual iron species. In the and Al2O3 phases, well stabilized Fe(iii) in T-d or O-h coordination was identified as the active species in HT-deN(2)O., Katalytická aktivita série katalyzátorů FeOx/Al2O3 připravených za různých podmínek byla testována pro vysokoteplotní rozklad N2O (HT-deN2O) v komplexní směsi vznijkající při spalování amoniaku, čímž byly simulovány podmínky z výroben kyseliny dusičné. Byla studována stabilita katalyzátorů během dlouhodobé (12 dní) zátěže. Jak čerstvě připravené, tak i zestárlé katalyzátory vykazovaly více než 90% konverzi N2O v teplotním rozsahu 750-900 °C. Strukturní analýza ukázala, že FeOx/Al2O3 katalyzátory obsahovaly různá množství δ, θ a α aluminy a až 4 druhy iontu železa. Ve formách δ a θ Al2O3 je dobře stabilůizováno Fe(III) v Td nebo Oh koordinaci, které bylo identifikováno jako aktivní centrum v HT-deN2O.

In a previous publication, the authors described a chromatographic process for the selective separation of fission products and minor actinides from uranium and plutonium in nitric acid solution. This paper has evaluated commercially available ion exchange materials for capacity, rate of uptake and selectivity for some fission products (inactive) and cerium (iii) and (iv) as surrogate for Pu and U. The fission products studied where Cs, Sr and Zr as these for various reasons present major challenges for the existing PUREX process and waste management. The commercial resins evaluated were various sulfonic acid, chelate ion exchangers and an undisclosed inorganic material all supplied by Purolite Ltd.

The reprocessing of spent nuclear fuel is a very important step in the nuclear fuel cycle and one of the greatest ways to ensure the sustainability of the civil nuclear industry. In France, the PUREX process is used to separate the reusable Uranium and Plutonium from the fission products and minor actinides that will then be disposed as waste. The dissolution of the spent fuel is at the head-end of this process and thus has a big impact on the following stages. The present work was done in the context of the development of a model for the dissolution step that will be used to design the dissolution reactors of the future. Some of the inputs this model will need are the kinetic constants of the dissolution reactions, which are quite complex. To achieve this, the dissolution of small grains of UO2 was studied under several experimental conditions. An algorithm was developed with the software MatLab which takes as input the images of the grains taken at regular intervals during the dissolution and as an output the dissolution rates in nm/s and mol/m2 /s. The algorithm binarises the grain images in order to have a clear distinction between grain and background, follows the area and perimeter of the oxide grains throughout the dissolution and finally calculates the wished results. The dissolution speeds at different experimental conditions will allow for the calculations of kinetic constants and activation energies which will then feed the dissolution model., Outgoing

Presents the Ramsen demonstration, a chemical demonstration that involves the reaction between copper and concentrated nitric acid. Outlines Ira Ramsen's description of the experiment, a modified version of it, the interpretation, and applications. (JRH)

In this study, the performance of different acid treated Myanmar Natural Clay (Mabisian) was conducted the pyrolysis of mixed plastic wastes, 40% high density polyethylene, 30% polypropylene, 25% low density polyethylene and 5% polystyrene. Mabisian clay was refluxed with different concentration of nitric acid (2M, 4M, 6M, 8M, 10M, 12M and 14M) at 100ºC for 3hrs followed by calcination at 500ºC for 1hr. The physico-chemical characteristics of resulted leached clay were studied by X-Ray Fluoresence spectroscopy (XRF), X-Ray Diffraction (XRD) and Fourier Transformed Infrared Spectroscopy (FTIR). The pyrolytic oil was characterized by Gas Chromatography – mass spectopy (GC-MS). XRF and FTIR studies indicated that acid treatment under reflux condition lead to the removal of octahedral Al3+ cations along with other impurities. The chemical treatment increased the Si/Al ratio. The maximum liquid yield (75%) was obtained at 12 M nitric acid, 3hr reaction time and 100 º C reaction temperatures. In addition, the percent peak area of gasoline range hydrocarbon was obtained 55.6% at optimum condition. Thus, the treated clay can be used as promising as catalyst support.

The nitrous oxide is determined by the content of (NOx) in the strong nitric acid, the increase of nitrous oxide by the way of either acid decomposition or temperature modification[1], [2] influence the safe production of military products and environmental pollutions[3]. The required specifications of the acids should meet the requirement of desired industry and safety during the transportations from site to site and storage. If the specifications (nitrous oxide) changed rapidly during transportation, decomposition takes place. It is believed that the Sudanese ambient temperature plays the main role. The strong nitric acid that has been stored for long time and transferred away will thermally and catalytically decompose and specifications will change. This study aims to develop a set of preliminary guide lines and recommendations for stabilizing the nitrous oxide (HNO2) in strong nitric acid. The equilibrium relations between acids systems (Nitrous oxide NOx expressed by "nitrous acid HNO2 concentration" and strong nitric acid HNO3) were reviewed and explained. The effects of Sudan ambient temperatures on acceleration of nitrous oxide (HNO2) in strong nitric acid, determine the optimum cooling temperature to slow the decomposition and to stabilize the nitrous oxide were investigated. This is done through incubation of three samples of strong nitric acid (97.5%) at the temperatures 20°C, 25°C and 30°C. Laboratory analysis was done to observe the nitrous oxide exit rate as function of temperatures, concentration of strong nitric acid within four days, Table I, II, III and Fig. 2, 4, 6 show the obtained experimental data. A noticeable increase of nitrous oxide at respective temperatures (20 0C, 25 0C, 30 0C) at the beginning was observed then the curve levels after three days’ incubation. It is concluded that (200C) is the higher temperature at which the strong nitric acid is either stored or transported. Hence it is the optimum temperature to slow the decomposition a

While observed mesospheric polar nitric acid enhancements have been attributed to energetic particle precipitation through ion cluster chemistry in the past, this phenomenon is not reproduced in current whole-atmosphere chemistry-climate models. We investigate such nitric acid enhancements resulting from energetic electron precipitation events using a recently developed variant of the Whole Atmosphere Community Climate Model (WACCM) that includes a sophisticated ion chemistry tailored for the D-layer of the ionosphere (50-90 km), namely WACCM-D. Using the specified-dynamics mode, i.e., nudging dynamics in the troposphere and stratosphere to meteorological re-analyses, we perform a one-year long simulation (July 2009-June 2010) and contrast WACCM-D with the standard WACCM. Both WACCM and WACCM-D simulations are performed with and without forcing from medium-to-high energy electron precipitation, allowing a better representation of the energetic electrons penetrating into the mesosphere. We demonstrate the effects of the strong particle precipitation events which occurred during April and May 2010 on nitric acid and on key ion cluster species, as well as other relevant species of the nitrogen family. The one-year-long simulation allows the event-related changes in neutral and ionic species to be placed in the context of their annual cycle. We especially highlight the role played by medium-to-high energy electrons in triggering ion cluster chemistry and ion-ion recombinations in the mesosphere and lower thermosphere during the precipitation event, leading to enhanced production of nitric acid and raising its abundance by two orders of magnitude from 10-4 to a few 10-2 ppb.

Exergy analysis for Nitric acid production plants are very few and many are outdated. This study aims to support existing scientific studies and incite new investigations of exergy analysis in modern times. An advanced exergy analysis was applied to a production plant with a capacity to process 350 tons/day of nitric acid at a concentration of 55%. The catalytic oxidation of ammonia, condensation and absorption of nitrous gases are considered as the principal process in the nitric acid production. The total destroyed exergy was 46772,55 KW. The component with the greatest impact was the catalytic converter, which presented 75.1% of the total avoidable exergy destruction rate of the plant. These findings are relevant as they can potentially reduce costs of nitric acid production. Copyright © 2018 ASME.

An optimization of temperature, time, and extracting agent concentration of pectin extraction from sunflower heads using sodium citrate and nitric acid (SP-SC and SP-NA) was carried out. At optimal conditions, the yield of extraction with nitric acid (SPO-NA) was twofold greater than the corresponding with sodium citrate (SPO-SC) (14.3 versus 7.7%, respectively). Regarding pectin structure, the galacturonic acid (GalA) content in both, SPO-SC and SPO-NA, was similar (∼85%). However, SPO-NA showed lower molecular weight (Mw) (88.9 kDa) and neutral sugar content (4%) than SPO-SC (464 kDa, 9%), indicating that nitric acid deeply degraded pectin structure. These differences derived into dissimilar behavior in their technological functionality. SPO-SC showed higher viscosity and better emulsifying capacity than SPO-NA, although any of them were able to stabilize the oil/water emulsion. Both sunflower pectins formed gels with Ca2+ (75 mg/g of pectin) at pH 3.0. However, when sucrose was added, the gels formed by SP-SC and 20% sucrose presented the same hardness as those of SP-NA with 40% sucrose. These results suggest that the pectin extracted with sodium citrate, an eco-friendly agent, could be a promising ingredient, with good thickening and gelling properties.

Measuring the composition of the stratosphere, and understanding the processes regulating it, have become,in the last few decades, top priorities in the scientific community, particularly since the discovery ofthe ozone hole in the 1980s. While a lot has indeed been done in monitoring ozone, other constituents also influence the stratosphere’s composition, and interfere namely with ozone, affecting its chemical and dynamical balance. Among these is nitric acid (HNO3 ) which is a reservoir for ozone depleting NOx ,but also a key player in the formation of polar stratospheric clouds which, by turning inert species into active radicals, enhance the ozone depletion further. The nadir-viewing IASI instrument is a very good means of obtaining simultaneous data of nitric acid and ozone. Indeed, it measures the radiation of the Earth’s atmosphere in the thermal infrared spectral range, which allows it to measure even at night. This is crucial to the study of polar processes, since they occur mostly during the polar winter, when no light reaches these latitudes. Thanks to its design and its technical characteristics, the IASI instrument provides data all-year round, for every location on the Earth. The purpose of this work is to use this unique set of IASI data to understand what drives the variability of HNO3 in the stratosphere. No study so far has focused on the factors affecting the time and spatial distributions of nitric acid to the extent and scale we propose here. We aim to identify and quantify these factors, and to compare them with the drivers of ozone variability. Nitric acid data are thus obtained for the 10 years of IASI observation (2008 − 2017), and vertical profiles are retrieved in near-real time thanks to the FORLI algorithm developed at ULB. The first part of the present work provides a detailed characterization of the IASI FORLI-HNO3 data set in terms of vertical sensitivity and errors. We show that the HNO3 maximum is found around 20 km altitude, where we als, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

A feasibility study was carried out to improve conventional recycling processes of used X-ray film, where silver was recovered mainly by concentrated nitric acid leaching. In the X-ray film, an emulsion layer containing silver is attached to polyester film base, and the enhancement of Ag leaching was expected by separating the emulsion layer from the polyester film base using methyl ethyl ketone (MEK), because the separation could increase the contact surface between nitric acid and Ag in the emulsion layer. First, the separation behaviors using MEK were investigated and the separation efficiencies of the emulsion layer increased with increasing temperature but decreasing film size and pulp density. The separation efficiency increased to 100% in MEK solution within 3 min under the following conditions; temperature 50°C; setting agitation speed 400 rpm; pulp density 50 g/L; film size 1 © 1 cm. In the followed nitric acid leaching test, the leaching result using the separated emulsion layer showed higher leaching efficiency than that using the unseparated X-ray film. Second, the effect of adding MEK to nitric acid leaching on the leaching efficiency of Ag was investigated by considering the amount of MEK added and temperature as experiment factors. The leaching efficiency of Ag increased with increasing the amount of MEK to 5%, but further addition of MEK to 7% rather reduce the leaching efficiency. With 5% of MEK addition, the leaching efficiency of Ag increased up to 95.9% in 120 min at 50°C whereas it increased and then decreased to 2.7% in the test at 70°C due to the formation of AgCl. These results indicate that the leaching efficiency of Ag could be enhanced using MEK in the nitric acid process for the recovery of Ag from the used X-ray film.

The processing of refractory gold-containing concentrates by hydrometallurgical methods is becoming increasingly important due to the depletion of rich and easily extracted mineral resources, as well as due to the need to reduce harmful emissions from metallurgy, especially given the high content of arsenic in the ores. This paper describes the investigation of the kinetics of HNO3 leaching of sulfide gold-containing concentrates of the Yenisei ridge (Yakutia, Russia). The effect of temperature (70–85 °C), the initial concentration of HNO3 (10–40%) and the content of sulfur in the concentrate (8.22–22.44%) on the iron recovery into the solution was studied. It has been shown that increasing the content of S in the concentrate from 8.22 to 22.44% leads to an average of 45% increase in the iron recovery across the entire range temperatures and concentrations of HNO3 per one hour of leaching. The leaching kinetics of the studied types of concentrates correlates well with the new shrinking core model, which indicates that the reaction is regulated by interfacial diffusion and diffusion through the product layer. Elemental S is found on the surface of the solid leach residue, as confirmed by XRD and SEM/EDS analysis. The apparent activation energy is 60.276 kJ/mol. The semi-empirical expression describing the reaction rate under the studied conditions can be written as follows: 1/3ln(1 - X) + [(1 - X)-1/3 - 1] = 87.811(HNO3)0.837(S)2.948e-60276/RT·t. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.

Thermodynamic and kinetic features studies of polymetallic sulfide industrial waste nitric acid leaching were carried out. Elemental and phase composition of investigated raw material were studied with X-ray diffraction and electron microscopy methods. Calculations of the Gibbs energy change for the likely reactions of sulfide minerals with nitric acid were performed. In order to determine the most probable conditions of the sulfide industrial waste leaching in nitric acid, as well as the mutual influence of the produced pulp components on the performance of the process, the kinetics evaluation of multicomponent sulfide industrial waste in a nitric medium was studied using mathematical methods.