Increasing HNO3 Concentration Research Articles

Effect of nitric acid concentration on corrosion behavior of CrFeCoNi high entropy alloy

CrFeCoNi high entropy alloy (HEA) was prepared by the method of vacuum melting. Its corrosion behavior in HNO3 solution with different concentrations was studied. The electrochemical test results indicated that the corrosion resistance firstly increased with increasing HNO3 concentration from 0.1 M to 4 M, and then decreased with further increasing HNO3 concentration to 6 M. The CrFeCoNi HEA exhibited the best corrosion resistance in 4 M HNO3 solution. The discrepancy of corrosion property in different concentration of HNO3 solutions could be attributed to the different protection of passive film formed on HEA. XPS results indicated that the content of Cr2O3 in the passive film initially increased with increasing HNO3 concentration from 0.1 M to 4 M, and then decreased with further increasing HNO3 concentration to 6 M. Higher content of Cr2O3 in the passive film was responsible for better corrosion property.

Computational Foretelling and Experimental Implementation of the Performance of Polyacrylic Acid and Polyacrylamide Polymers as Eco-Friendly Corrosion Inhibitors for Copper in Nitric Acid.

Copper is primarily used in many industrial processes, but like many other metals, it suffers from corrosion damage. Polymers are not only one of the effective corrosion inhibitors but also are environmentally friendly agents in doing so. Hence, in this paper, the efficacy of two polyelectrolyte polymers, namely poly(acrylic acid) (PAA) and polyacrylamide (PAM), as corrosion inhibitors for copper in molar nitric acid medium was explored. Chemical, electrochemical, and microscopic tools were employed in this investigation. The weight-loss study revealed that the computed inhibition efficiencies (% IEs) of both PAA and PAM increased with their concentrations but diminished with increasing HNO3 concentration and temperature. The results revealed that, at similar concentrations, the values of % IEs of PAM are slightly higher than those recorded for PAA, where these values at 298 K reached 88% and 84% in the presence of a 250 mg/L of PAM and PAA, respectively. The prominent IE% values for the tested polymers are due to their strong adsorption on the Cu surface and follow the Langmuir adsorption isoform. Thermodynamic and kinetic parameters were also calculated and discussed. The kinetics of corrosion inhibition by PAA and PAM showed a negative first-order process. The results showed also that the used polymers played as mixed-kind inhibitors with anodic priority. The mechanisms of copper corrosion in nitric acid medium and its inhibition by the tested polymers were discussed. DFT calculations and molecular dynamic (MD) modelling were used to investigate the effect of PAA and PAM molecular configuration on their anti-corrosion behavior. The results indicated that the experimental and computational study are highly consistent.

Highly efficient uptake of tetravalent actinide ions from nitric acid feeds using an extraction chromatography material containing tetra-n-butyl diglycolamide and a room temperature ionic liquid

An extraction chromatography (XC) material containing N,N,N’,N’-tetra-n-butyl diglycolamide (TBDGA) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulphonyl) imide (C4mim∙NTf2), a room temperature ionic liquid, was used for the uptake of the tetravalent actinide ions Th(IV), Np(IV), and Pu(IV) from nitric acid feed solutions. The uptake of the metal ions followed the trend: Th(IV) < Np(IV) < Pu(IV), which is the same as that of their ionic potential values. While a decrease in the Np(IV) and Pu(IV) uptake was seen with increasing HNO3 concentration at lower acidities, an opposite trend was observed at higher acidities. Th(IV) uptake was not affected with the acid concentration. In view of the very high uptake and its importance in the nuclear fuel cycle, the major part of the studies was carried out with Pu(IV) ion. The loaded Pu(IV) was back extracted from the XC material using a mixture of 0.5 M oxalic acid and 0.5 M nitric acid. The Pu(IV) uptake by the XC material was fitted into different kinetic and isotherm models. The results conformed to the pseudo-second order kinetic model and the Langmuir monolayer sorption model. Column studies were carried out using a feed having 1.6 mg/L Pu solution in 3 M HNO3. While the breakthrough was obtained after passing ca. nine bed volumes, a sharp elution peak was obtained with >99% recovery in about seven bed volumes.

Novel two-step process for remediation of Cs-contaminated soil assisted by magnetic composites

In this study, a new approach to remediate Cs+-contaminated soil using magnetic composites to improve both the efficiency of separation of clay particles and Cs+ desorption is proposed. An ultrasonic dispersion and magnetic separation process were first performed to selectively remove clay particles from soil. In the soil dispersion solution, polyethylenimine-grafted Fe3O4 nanoparticles were selectively bonded with clay particles through electrostatic attraction, enabling the clay particles to be easily separated from the solution under an external magnetic field. In a Cs+ desorption process, Cs+ removal increased with increasing HNO3 concentration and temperature; the addition of K+ to the acid solution further enhanced Cs+ desorption by replacing Cs+ on the accessible sites of the sand. The addition of a magnetic adsorbent (Fe3O4@SiO2@KTiFC, where KTiFC is potassium titanium(IV) hexacyanoferrate) to the acid treatment substantially improved Cs+ desorption (95.2%) by preventing re-adsorption of Cs+ onto the sand. Based on these results, we evaluated the applicability of the proposed process to the decontamination of radioactive soil. The clay separation process substantially reduced the radioactivity level of the soil from 1630 to 222 Bq/kg by concentrating most of the 137Cs into the magnetic fraction. After treatment of the residual sand using the optimized Cs+ desorption method, the final radioactivity of the treated soil (73.5 wt% of initial soil) was 53 Bq/kg, which is less than the clearance level (100 Bq/kg). Therefore, the proposed method is potentially an effective and practical approach for the decontamination of radioactive soil.

Gravimetric and data analysis of the corrosion resistance behaviour and inhibition of C26000 brass in dilute HNO3 solution

The corrosion resistance of as-received and heat treated C26000 brass (annealed and quenched) was evaluated by gravimetric analysis in 0.5 M, 1 M, 1.5 M, 2 M, 2.5 M, 3 M and 3.5 M HNO3 solution. Generally, corrosion rate of C26000 increased with increase in HNO3 concentration and varies significantly with respect to observation time. Results showed that heat treatment has no influence on the corrosion resistance of the brass heat treated brass compared to the as-received sample. Application of garlic extracts in HNO3 solution at 0.5 M significantly decreased the corrosion rate of C26000 60% concentration with inhibition value of 79.46%. The garlic extract exhibited significant concentration dependent behaviour and its inhibition performance varies with observation time. Statistical evaluation showed the standard deviation values of as-received and heat treated C26000 varied with respect to mean inhibition data. However, variation increased with HNO3 concentration due to thermodynamic instability with respect to observation time. In the presence of the garlic extracts, the high standard deviation values at the lowest and highest garlic concentration signify significant variation with observation time and thermodynamic instability. Evaluation through analysis of variance shows HNO3 concentration and observation are statistically irrelevant to the corrosion rate output of as-received and heat treated C26000. In the presence of garlic extracts only the extract concentration is statistically relevant with value of 90.52%.

Competitive extraction of Li, Na, K, Mg and Ca ions from acidified aqueous solutions into chloroform layer containing diluted alkyl phosphates

Alkyl phosphates were extensively used in liquid–liquid extraction of lanthanides and actinides, but to a lesser extent for alkali and alkaline earth metals. The high amount of alkyl phosphate, which is usually used in the organic layer (>40 wt%), is not favoured due to its corrosive effect and toxicity. In the present work, diluted chloroform solutions (20.0 mM) of tri-n-butyl phosphate (TBP), tris(2-ethylhexyl) phosphates (TRIS) and bis(2-ethylhexyl) phosphate (BIS) were investigated for their extraction of Li, Na, K, Mg and Ca ions. The extraction experiments were conducted on 7.0 M HNO3 aqueous solutions containing 60.0 mM of metal ions in binary (Li+ and Mg2+), ternary (Li+, Na+ and K+) and quinary (Li+, Na+, K+, Mg2+ and Ca2+) mixtures. The Li+ selectivity over Mg2+ was very high in the binary system. Remarkably, increasing HNO3 concentration in the aqueous layer had opposing effect on the extraction of Li+ (positive) and Mg2+ (negative). However, the selectivity for Li+ became less dramatic in the case of ternary and quinary system, though the selectivity varied with initial metal concentrations. The amounts of water and NO3– transferred into the organic layer demonstrated their synergistic effect on extracting metal ions. In the ternary and quinary systems, the total concentrations of metal ions in the organic layer (ranged from 49 to 85 mM) were higher than the concentration of ligand in the organic layer (20.0 mM), suggesting that metal ions may be extracted into water/ligand/NO3– aggregates in the organic layer. TBP, TRIS and BIS do not have significant difference in their extraction behaviour. The FTIR results indicated formation of P+-O-M+/M2+ in the solid TBP/metal complex.

Nitric acid pressure leaching of limonitic laterite ores: Regeneration of HNO3 and simultaneous synthesis of fibrous CaSO4·2H2O by-products

An innovative technology, nitric acid pressure leaching of limonitic laterite ores, was proposed by our research team. The HNO3 regeneration is considerable significance for the improvement of the proposed technology and its commercial application, but it has not been systematically investigated. Herein, regenerating HNO3 from Ca(NO3)2 solution with low-cost H2SO4, and simultaneous synthesis of fibrous CaSO4·2H2O by-products were studied. As a theoretical basis, the solubility of CaSO4·2H2O in HNO3 medium is studied. It is concluded that the solubility of CaSO4·2H2O increases with increasing temperature or increasing HNO3 concentration, which has considerable guiding significance for the subsequent experimental research and analysis. Then, the effects of various factors on the residual Ca2+ concentration of filtrate, the regenerated HNO3 concentration and the morphology of synthesized products are investigated using ICP-AES and SEM. And the effect mechanism is also analyzed. The results indicate the regenerated HNO3 concentration reaches 116 g/L with the residual Ca2+ concentration being 9.7 g/L at the optimum conditions. Moreover, fibrous CaSO4·2H2O by-products with high aspect ratios (length, 406.32 µm; diameter, 14.71 µm; aspect ratio, 27.62) can be simultaneously synthesized.

Extraction of Some Actinide Ions from Nitric Acid Feeds Using N, N-di-n-hexyloctanamide (DHOA) in an Ionic Liquid

Liquid–liquid extraction studies of $${\text{UO}}_{2}^{{2 + }} $$ , $$ {\text{NpO}}_{2}^{{2 + }} $$ , Pu(IV), Np(IV), and Pu(III) were carried out from nitric acidic feeds using N,N-di-n-hexyloctanamide (DHOA) in 1-butyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide (C4mim·NTf2). The distribution studies indicated strikingly different trends in the extraction of tetra- and hexa-valent actinide ions with varying nitric acid concentration. While the distribution ratio values for $${\text{UO}}_{2}^{{2 + }} $$ and $$ {\text{NpO}}_{2}^{{2 + }} $$ were found to decrease with increasing HNO3 concentration up to 1 mol·L−1 HNO3 and did not change thereafter, those obtained for Pu4+ and Np4+ showed monotonic increases over the entire range of acidity. On the other hand, Pu3+ was poorly extracted in the lower acidity range up to 4 mol·L−1, beyond which a sharp increase in the extraction was seen. The nature of the extracted species was obtained using several studies where the ligand and nitrate ion concentrations were varied while keeping the others constant using slope analysis.

Chlorine inclusion mechanism in high purity copper electrorefining from nitric acid system

Abstract 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 behavior of this inclusion. Experimental results show that the increase of HNO3 concentration is favorable 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 ~35 °C with current density not exceeding 25 mA/cm2. Based on the theoretical studies, an optimized copper electrorefining experiment was designed to simulate the industrial electrolysis, by which high purity copper can be obtained with chlorine inclusion less than 10 μg/g and current efficiency higher than 90%.

Effect of the acid activation on a layered titanosilicate AM-4: The fine-tuning of structural and physicochemical properties

In this work we investigated the microporous layered titanosilicate AM-4 (Aveiro-Manchester material number 4) of a synthetic analogous the mineral Lintisite having edge-shared brookite-type TiO6 chains. The objective of our work was to verify the effects of the acid activation on the AM-4 properties, treated with 0.0625–0.25 M HNO3. The results of the physicochemical characterization by SEM, XRD, IR and DR UV–vis spectroscopy, nitrogen adsorption/desorption at 77 K have provided evidences that texture, chemical composition, structural and physicochemical properties of AM-4 could be adjusted by treatment with 0.0625–0.25 M HNO3. According to the method of mass titration, surface acidity (pHPZC) of AM-4 roses with increasing HNO3 concentration, which was in accord with the increase of the reaction rate and yield of 1,5-benzodiazepine in the reaction of cyclocondansation between 1,2-phenylenediamine and acetone.

Formation of Inverted Pyramid‐Like Submicron Structures on Multicrystalline Silicon Using Nitric Acid as Oxidant in Metal Assisted Chemical Etching Process

H2O2 is predominantly used as an oxidizer in traditional metal assisted chemical etching (MACE), showing a high consumption rate due to its instability at room temperature. In this work, low concentration HNO3 instead of H2O2 is investigated in Ag‐assisted chemical etching process for multicrystalline silicon (mc‐Si) wafer. In comparative experiments, black silicon wafers with a surface reflection of 6.46% are obtained using HNO3 with only 5% molar concentration quantity of H2O2. After a post nanostructure rebuilding treatment, nano‐scale inverted pyramid‐like structures are obtained. SEM images reveal that increase in HNO3 concentration lead to an increase in surface roughness with enlarged structure size. Furthermore, a linear increase in etching rate is observed when AgNO3 concentration raised from 0 to 0.8 × 10−3m. The activation energy of 95.4 eV for the HNO3/HF‐Si reaction catalyzed by Ag is obtained by Arrhenius equation. The outcomes demonstrate HNO3 as a potential alternative to conventional oxidizer H2O2 in traditional MACE process.

Separation of Palladium along with Minor Actinides byisoBu-BTP/SiO2-P Adsorbent from High-Level Liquid Waste

Aiming at the separation of Pd(II) along with MA(III) from high-level liquid waste, a porous silica based adsorbent isoBu-BTP/SiO2-P was prepared. The adsorption properties of isoBu-BTP/SiO2-P toward Pd(II) were investigated. It was found that with the increase of HNO3 concentration, Pd(II) adsorption ability increased initially as HNO3 concentration increased until 1 M, then remained unchanged as HNO3 concentration further increased. The adsorption kinetics and isotherm of Pd(II) onto isoBu-BTP/SiO2-P fit well with the pseudo-second-order rate law and Langmuir adsorption model, respectively. The adsorption thermodynamic parameters revealed that the adsorption process was spontaneous and endothermic. A hot test utilizing isoBu-BTP/SiO2-P packed column was conducted and the simultaneous separation of Pd(II) and MA(III) was achieved from solution by using 0.01 M HNO3-0.1 M TU and 0.01 M HNO3-0.01 M DTPA as eluents, respectively. The Pd(II) with isoBu-BTP/SiO2-P complex was illustrated to be 1:1 type by HRMS...

Corrosion and Tribocorrosion Behaviors of Amorphous Carbon Films in Nitric Acid Solutions

The corrosion and tribocorrosion behaviors of Type 304 stainless steel coated by two different amorphous carbon films, including undoped and Cr-doped amorphous carbon films, were investigated in HNO3 solution, and bare Type 304 stainless steel was used for comparison. In static-corrosion environment, the corrosion current densities of the carbon-based films were decreased by 41% to 97%, when compared with stainless steel, thus suggesting that the corrosion protection properties of the films were excellent. Tribocorrosion tests were conducted to synchronously monitor the open-circuit potential and friction coefficient of the films, and the friction coefficient increased with the increase of HNO3 concentration. Therefore, the carbon-based films could effectively improve the wear resistance of Type 304 stainless steel in HNO3 solutions.

γ-Ray radiolysis of acetohydroxamic acid in HNO3 and its radiolytic product

Acetohydroxamic acid (AHA) is a novel salt-free reagent used for the separation of Pu and Np from U in the advanced Purex process. This paper reports the γ-ray damage of AHA in HNO3 and its radiolytic product. For 0.2 mol L−1 AHA in 0.2–2.0 mol L−1 HNO3 irradiated at a dose of 5–25 kGy, the radiolytic rate of AHA is 6.63–77.5%, and it increases with the HNO3 concentration and absorbed dose. The main radiolytic gases are N2O and H2, with volume fractions of (0.500–16.2) × 10−2 and (1.30–11.8) × 10−3, respectively, and they increase with the absorbed dose; the H2 volume fraction decreases with increasing HNO3 concentration. The main liquid radiolytic products are CH3COOH and HNO2, and their concentrations are (3.40–19.7) × 10−2 and (0.200–4.80) × 10−3 mol L−1, respectively, which increase with the HNO3 concentration. Since a significant concentration of HNO2 is present in the irradiated AHA-HNO3 solution, a holding reductant must be used to destroy HNO2 and stabilize Pu(III) and Np(V) when AHA is applied for the separation of Pu and Np from U.

Liquid-liquid extraction and facilitated transport of f-elements using an N-pivot tripodal ligand

Diglycolamide (DGA)-functionalized tripodal ligands offer the required nine-coordinated complex for effective binding to a trivalent lanthanide/actinide ion. A N-pivot tripodal ligand (TREN-DGA) containing three DGA pendant arms was evaluated for the extraction and supported liquid membrane transport studies using PTFE flat sheets. Solvent extraction studies indicated preferential extraction of 1:1 (M:L) species, while the metal ion extraction increased with increasing HNO3 concentration conforming to a solvated species extraction. Flat sheet-supported liquid membrane studies, carried out using 4.0 × 10−3 M TREN-DGA in 95% n-dodecane + 5% iso-decanol indicated faster mass transport for Eu3+ ion as compared to Am3+ ion. The determined transport parameters indicated slow diffusion of the M-TREN-DGA (M = Am or Eu) complex being the rate-determining step. The transport of lanthanides and actinides followed the trend: Eu3+ > Am3+∼ Pu4+ >> UO22+ and Am can be selectively separated from a mixture of U and Pu by oxidizing the latter to its +6 oxidation state. The liquid membrane stability was not encouraging and was deteriorating the transport efficiency with time, which was attributed to carrier loss into the aqueous phases.

Extraction of uranium(VI) from nitric acid solutions using N,N-dihexyloctanamide in ionic liquids: Solvent extraction and spectroscopic studies

ABSTRACTLiquid-liquid extraction studies of uranium(VI) were carried out from nitric acid medium using di-n-hexyloctanamide (DHOA) in several room-temperature ionic liquids (RTIL). The extraction of the metal ion as a function of nitric acid concentration showed different trends based on the alkyl substituents of the RTIL. While the DU values decreased with increasing HNO3 concentration (up to ca. 0.5 M) with [C4mim][NTf2] and [C6mim][NTf2], almost no change was seen with [C8mim][NTf2]. This suggested that while a cation-exchange mechanism is operative with the former diluents, which was to a much lower extent for the latter. The extracted species were found to contain about 2 molecules of DHOA from the feed solutions containing either 0.01 M and 4 M HNO3, which was arrived at from the ligand-concentration-variation experiments. Recycling studies were also performed by carrying out stripping and radiolytic stability studies. The nature of the extracted species as ascertained from the UV-visible spectrophotometry studies indicated similarity between the extracts obtained in RTIL medium, which were entirely different from that observed with n-dodecane as the diluent.

Kinetics of Pu(VI) reduction with carbohydrazide in nitric acid

The kinetics of the Pu(VI) reduction with carbohydrazide in nitric acid solutions was studied by spectrophotometry. The reaction rate increases with increasing carbohydrazide concentration and temperature and decreases with increasing HNO3 concentration. The reaction order with respect to Pu, carbohydrazide, and HNO3 is 1, 2.3, and–3, respectively. The activation energy of the reaction is 111 kJ mol–1. The final reduced Pu form is Pu(III), with Pu(V) being an intermediate.

Recovery of palladium by silica/polymer-based 2,6-bis(5,6,7,8-tetrahydro-5,8,9,9-tetramethyl-5,8-methano-1,2,4-benzotriazin-3-yl)pyridine adsorbents from high level liquid waste

ABSTRACTThe adsorption properties of a porous silica-based adsorbent 2,6-bis(5,6,7,8-tetrahydro-5,8,9,9-tetramethyl-5,8-methano-1,2,4-benzotriazin-3-yl)pyridine (Me2-CA-BTP/SiO2-P) towards Pd(II) were investigated. The adsorption ability of Me2-CA-BTP/SiO2-P towards Pd(II) increased dramatically with the increase of HNO3 concentration and showed a saturated uptake of Pd(II) after the HNO3 concentration reached 3 mol/dm3. It was found that nitrate ion would participate in the adsorption reaction. Palladium adsorption kinetic and isotherm were in accordance with the pseudo-second-order rate law and Langmuir isotherm adsorption model, respectively. Thiourea could effectively elute the adsorbed palladium from Me2-CA-BTP/SiO2-P. Adsorption studies with high level liquid waste elements showed a high selectivity towards Pd(II) over other fission product elements in ≥3 mol/dm3 HNO3 solution. The stability of Me2-CA-BTP/SiO2-P against HNO3 was satisfied for the reason of the adsorption performance keeping for Pd(II) after a long-time contact with HNO3 solution. The adsorbent performed good γ-irradiation stability in dry state and low concentrations of HNO3. The presence of HNO3 enhanced the radiolysis and the adsorbent still reserved a presentable adsorption amount after γ-irradiation in 3 mol/dm3 HNO3.

Possibility of using hydrogen peroxide for trapping nitrogen oxide at radiochemical enterprises

Published data on the reaction of H2O2 with nitrogen oxides and HNO2 were analyzed and summarized as applied to the problems of trapping nitrogen oxides from off-gases. H2O2 reacts only with NO and HNO2 dissolved in aqueous solution, and the NO solubility increases with increasing HNO3 concentration. Examples of enhancing the efficiency of trapping nitrogen oxides by using Н2О2 are presented.

Selective extraction of americium(III) over europium(III) ions in nitric acid solution by NTAamide(C8) using a novel water-soluble bisdiglycolamide as a masking agent

Abstract A novel water-soluble ligand of N,N,N‴,N‴-tetraethyl-N′,N″-ethidene bisdiglycolamide (TEE-BisDGA) was synthesized and used as a masking agent for selective extraction of Am(III) over Eu(III) from HNO3 solution by N,N,N′,N′,N″,N″-hexaoctylnitrilotriacetamide (NTAamide(C8)) in kerosene. Influences of acidity, concentration of water-soluble ligands and extractant as well as nitrate ions on the distribution ratios (D) and separation factors (SF) of Am(III) and Eu(III) were investigated. In the range of examined acidity from 0.001 to 0.2 mol/L, DAm and DEu decreased with the increase of HNO3 concentration. Using 0.1 mol/L NTAamide(C8) as an extractant, the maximum SFAm/Eu of 26 can be obtained in the presence of 0.01 mol/L TEE-BisDGA in aqueous phase with pH of 3.0, which was significantly higher than that case with no TEE-BisDGA. Job's method and mole ratio method were employed for extraction mechanism research. It has been shown that Am(III) and Eu(III) formed di-solvated species with TEE-BisDGA and mono-solvated species with NTAamide(C8), respectively. Moreover, the stability constants logβ values were obtained from UV–vis adsorption spectroscopic titration for Nd(III) complexes with TEE-BisDGA and N,N,N′,N′-tetraethyldiglycolamide (TEDGA), which indicated that TEDGA had a stronger complex ability than TEE-BisDGA.