Nitric Acid System Research Articles

Adsorption and Desorption Behavior and Mechanism of Ruthenium in Nitrite-Nitric Acid System.

Ruthenium is required to separate from high-level liquid waste (HLLW) because Ru is a valuable resource and is negatively influential on the vitrification process of HLLW. However, the separation of Ru is very challenging due to its complicated complexation properties. In this study, the adsorption and desorption characteristics of ruthenium on a synthesized SiPyR-N3 (weak-base anion exchange resin with pyridine functional groups) composite were investigated in nitric acid and nitrite-nitric acid systems, respectively, and the adsorption mechanism was explored. The experimental results showed that SiPyR-N3 has a significantly better adsorption effect on Ru in the nitrite-nitric acid system than in the nitric acid system, with an increase in the adsorption capacity of approximately three times. The maximum adsorption capacity of Ru is 45.6 mg/g in the nitrite-nitric acid system. The SiPyR-N3 possesses good adsorption selectivity (SFRu/other metal ions is around 100) in 0.1 M NO2--0.1 M HNO3 solution. The adsorption processes of Ru in the two different systems are fitted with the pseudo-second-order kinetic model and Langmuir model for uptake kinetics and adsorption isotherms, respectively. The results obtained from the FT-IR, XPS, and UV absorption spectrometry indicate that NO2- was involved in the adsorption process either as a complexing species with the metal ions or as free NO2- from the solution. A 0.1 M HNO3 + 1 M thiourea mixed solution shows effective desorption performance, and the desorption efficiency can reach 92% at 328 K.

Oxidation Mechanism of Tetravalent Uranium in Nitric Acid System Synthesized by Hydrogen Reduction Process

Oxidation Mechanism of Tetravalent Uranium in Nitric Acid System Synthesized by Hydrogen Reduction Process

Study on Corrosion and Wear Behavior Mechanism of Reactor Material in Metastannic Acid Synthesis

AISI 316L, Ti2, and Zr1 are widely used in the selection of reaction still material, however, there is corrosion wear behavior in the use process. In this paper, the adsorption behavior of oxygen in Fe, Ti, and Zr is studied by the first principles method. Corrosion and wear behaviors of AISI 316L, Ti2 and Zr1 were studied by electrochemical corrosion and wear tests. The results show that AISI 316L can effectively resist the action of friction pair during wear by elastic modulus calculation. Oxygen is easily adsorbed at the top of the Fe(111) crystal plane and the bridge site of the Zr(110) crystal plane to form the most stable adsorption structure. The Ecorr of Zr1 (0.275 V) is greater than that of Ti2 (0.266 V) and AISI 316L (0.094 V), resulting in a ZrO2 passivated film with strong protection in the HNO3 solution. The wear rate of AISI 316L is higher than that of Zr1 and Ti2. In the selection of tin chemical reactor material, it is preferred that Zr1 can withstand corrosion and wear for a long time in a nitric acid system, which provides important guidance for corrosion and wear of reactor materials in the synthesis of tin acid.

Highly Selective Adsorption of 99TcO4-/ReO4- by a Novel Polyamide-Functionalized Polyacrylamide Polymer Material.

The treatment of radioactive wastewater is one of the major problems in the current research. With the development of nuclear energy, the efficient removal of 99TcO4− in radioactive wastewater has attracted the attention of countries all over the world. In this study, a novel functional polyamide polymer p-(Amide)-PAM was synthesized by the two-step method. The experimental results show that p-(Amide)-PAM has good adsorptive properties for 99TcO4−/ReO4− and has good selectivity in the nitric acid system. The kinetics of the reaction of p-(Amide)-PAM with 99TcO4−/ReO4− was studied. The results show that p-(Amide)-PAM has a fast adsorption rate for 99TcO4−/ReO4−, the saturated adsorption capacity reaches 346.02 mg/g, and the material has good reusability. This new polyamide-functionalized polyacrylamide polymer material has good application prospects in the removal of 99TcO4− from radioactive wastewater.

Extraction and separation of Pd(II) by N, N'-diethyl-N, N'-dicyclohexylmalonamide in a nitric acid system

This study indicated the extraction and separation of Pd(II) by N, N'-diethyl-N, N' -dicyclohexylmalonamide (DEDCHMA) from the aqueous nitric acid solution. The effects of extraction time, nitric acid concentration, diluent, extraction temperature, and extractant concentration on extraction distribution ratio were investigated. The extraction mechanism and the composition of the complex were further discussed based on FT-IR and slope analysis. Compared with N, N, N', N'-tetraoctyl diglycolamide (TODGA) and N, N, N', N'-tetracyclohexylmalonamide (TCHMA), the DEDCHMA showed higher extraction capacity for Pd(II), which is 46 and 15 times higher than that of TCHMA and TODGA, respectively. The stripping extraction ratio obtained in Pd(II)-loaded organic phase using thiourea or oxalic acid reached 99%. The extraction selectivity to Pd(II) and noble metals such as Ru(III), Rh(III), and some common base metals, such as Al(III), Fe(III), Ni(II), Cu(II), Zn(II), Ca(II), Mg(II), Pb(II), Sr(II), Cr(III) and CO(II), was also investigated. The results demonstrate that DEDCHMA can be used to treat and recover Pd(II) from nitrate-based wastes containing associated precious metals, such as Pd(II), Ru(III), Rh(III), and common base metal, as well as from the spent fuel reprocessing.

Parametric study on dispersed phase holdup and axial drop size distribution in a pulsed disc and doughnut extraction column

ABSTRACT A parametric study of the dispersed phase holdup, specific power consumption (P) and axial drop size distribution (ADSD) in a pulsed disc and doughnut column have been carried out with 30% Tri-Butyl Phosphate- 0.01 M nitric acid system. ‘P’ and holdup decreases with increasing percentage duty cycle and increases exponentially with increased pulsation. Whereas ‘P’ remains almost independent of total superficial velocity and phase flow ratio. At the top of the extraction section, the most uniform DSD have been observed. Subsequently, Unified empirical correlations have been developed over much wider range for predicting the holdup and Sauter mean diameter.

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%.

Interactions of the Bismuthate Anion with Alkali, Alkaline Earth, Lanthanide, and Actinide Metals in Nitric Acid Systems

The solubility, dissolution, and degradation of the bismuthate anion were studied in the presence of various metal ions. A molar extinction coefficient of the bismuthate species of 11.1 ± 0.2 L mol...

Thermodynamic modeling of the water – Nitric acid – Rare earth nitrate systems

An excess Gibbs energy model describing the properties of aqueous electrolyte solutions, mixed solvent electrolyte systems and nonelectrolyte systems, has been developed. The suggested electrolyte version of the Generalized Local Composition Model (eGLCM) contains three contributions to the excess Gibbs energy: a long–range electrostatic interaction term represented by the modified Pitzer-Debye-Hückel equation, which takes into account concentration dependence of the solution dielectric permittivity, the contribution of the short–range interaction between all the species, represented by the GLCM model, and the middle–range interaction term responsible for interactions involving charged species that are not explained by the long–range term. The developed model is applicable over a whole concentration range, from pure water to saturation and fused salts. The water – nitric acid system, 15 water – rare earth element nitrate systems (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) and eight water – nitric acid – REE nitrate systems (Y, La, Ce, Pr, Nd, Sm, Eu and Gd) have been modeled with the proposed electrolyte version of the Generalized Local Composition Model at 25 °C, using experimental data on both the vapor – liquid (VLE) and solid – liquid (SLE) equilibria, in a concentration range from dilute solutions to saturation. SLE data in the ternary systems were critically reviewed and correlated with the thermodynamic properties of the solutions.

Recovery of cerium(IV) in acidic nitrate solutions by solvent extraction with a novel extractant tris(2-ethylhexyl)phosphine oxide

The extraction of cerium(IV) (Ce(IV)) from a nitric acid (HNO3) system using a novel extractant, tris(2-ethylhexyl)phosphine oxide (TEHPO), was studied. The separation factors of Ce(IV)/Th(IV) and Ce(IV)/Ln(III) (La3+, Gd3+ and Lu3+) were found to be in the range of 60–127 and 121–827, respectively, in the HNO3 concentration range of 0.5–5.0 mol/L, showing high selectivity with TEHPO. The experimental results showed that TEHPO can effectively extract Ce(IV) from a HNO3 system quantitatively in a 2:1 form (molar ratio of TEHPO: Ce(IV)), which is unrelated to the experimental conditions, that is, factors such as HNO3 concentration, extractant concentration, and temperature. The loaded Th(IV) could be stripped efficiently using H2O, but Ce(IV) should be stripped using H2O2. The extraction mechanisms of HNO3 and Ce(IV) with TEHPO were determined through the slope analysis method, infrared spectroscopy (FT-IR), and electrospray ionization mass spectrometry (ESI-MS), and the extracted complexes were found to be HNO3·TEHPO and Ce(NO3)4·2TEHPO. Comparison of their extraction performances revealed that TEHPO shows a better interfacial phenomenon and higher extraction ability and saturation loading capacity than those of Cyanex923.

Effect of DGA substituent structure on rare earth extraction in nitric acid media

N substitutent group structure has great influence on the extraction and separation ability of amide extractant. In this paper, four different extractants with different structures, namely TODGA (N,N,N’,N’-tetraoctyl-3-oxa-diglycolamide), T2EHDGA (N,N,N’,N’-tetraisooctyl-3-oxa-diglycolamide), DPDODGA (N,N’-dipropyl-N,N’-dioctyl-3-oxa-diglycolamide) and DIPDODGA (N,N’-diisopropyl-N,N’-dioctyl-3-oxa-diglycol-amide) were investigated. The extraction ability of rare earth elements in nitric acid system was investigated to understand the relationship between chemical structure of the extractant and the extraction and separation properties of rare earth ions. The effects of nitric acid acidity, rare earth metal ion concentration and extractant concentration on the extraction were also investigated.

A novel extractant 2-Ethylhexyl Bis(2-ethylhexyl)phosphinate for cerium(IV) and fluorine extraction from nitric acid system

A novel extractant, 2-ethylhexyl Bis(2-ethylhexyl)phosphinate (EHBEHP, abbreviated as B), was synthesized for the extraction of Cerium(IV) (Ce(IV)) and fluorine (F(I)) from nitric acid (HNO3) media. The effects of HNO3 concentration, extractant concentration, F(I) concentration and the temperature on the Ce(IV) and F(I) extraction were studied and discussed. The experimental results show that EHBEHP has a strong ability to extract Ce(IV), while the presence of F(I) decreases the extraction ability of Ce(IV). The extraction process had nothing to do within the studied temperature range. The extraction of HNO3, Ce(IV) and Ce(IV)-F(I) were studied respectively, and the extracted complexes were found to be 2HNO3·EHBEHP, Ce(NO3)4·2EHBEHP and Ce(HF)(NO3)4·EHBEHP, individually. The extraction mechanisms were determined according to slope analysis method. Saturation loading capacity of Ce(IV) and F(I) extracted by 0.867 mol/L EHBEHP in HNO3 system was about 50.98 g/L and 5.67 g/L, respectively. The stripping experiment shows that 95.3% of stripping efficiency of Ce(IV) can be obtained with 2.4% H2O2. The FT-IR of extracted complexes were measured and characterized. EHBEHP shows higher extraction ability and saturation loading capacity compared with DEHEHP.

CFD Modeling of Single-Drop Hydrodynamics at Submerged Nozzles: Validation with TBP-Dodecane and Nitric Acid System and Parametric Analysis

ABSTRACTSolvent extraction is an important separation process having many applications in chemical process industry, wastewater treatment, and separation of nuclear materials in the front-end and back-end of the closed nuclear fuel cycle. It is essentially based on dispersion of one liquid phase into another immiscible liquid phase in the form of drops. This study, which is relevant to solvent extraction, is focused on computational fluid dynamics simulations of one of the mechanisms to generate dispersion in which drops are generated by flowing a liquid through a nozzle submerged in another immiscible liquid. Two different orientations of nozzles, vertically upward and vertically downward, are considered. Transient simulations are carried out using the phase-field method for tracking the interface between the two immiscible liquids. Validation has been done with the experimental data of 30%TBP-dodecane and nitric acid system. The validated model is used to perform parametric analysis to get insights into the effects of physical properties (interfacial tension, contact angle, and density difference) on drop formation phenomenon. The results from parametric analysis are used to obtain correlations to estimate drop diameter at upward-oriented and downward-oriented nozzles.

Drop formation at submerged nozzles: Comparison of aqueous dispersed and organic dispersed cases for TBP-dodecane and nitric acid system

Abstract Understanding the phenomena of formation of single drops is necessary to understand the hydrodynamics in solvent extraction equipment which are used for separation of nuclear materials. In this work, the phenomena of aqueous phase and organic phase drop formation at submerged nozzles are compared by conducting experiments with 30%TBP (v/v) in dodecane as the organic phase and nitric acid as the aqueous phase. Two different nozzles and three different nitric acid concentrations are used. For each nozzle and nitric acid concentration, velocity of the dispersed phase is varied. Drops of aqueous phase formed at downward oriented nozzles submerged in organic phase are observed to be smaller than the drops of organic phase formed at upward oriented nozzles submerged in aqueous phase. Correlations to estimate drop diameter are proposed.

Solubility and Complexation of the Bismuthate Ion in Nitric Acid Systems.

The dissolution rate and solubility of NaBiO3 have been investigated in nitric acid systems ranging from 4 to 6 M HNO3 and were found to be 58-76 μg/cm2·d and 490-830 mM, respectively. The presence of 50 mM U(VI) drastically increased the solubility to 540-1200 mM, while rates of dissolution were relatively unchanged. The solubility of NaBiO3 increased with an increase in U(VI) concentrations at 4 M HNO3, with log-log analysis indicating a one-to-one complex between Bi and U and infrared spectroscopic evidence monitoring uranyl stretching, suggesting complex formation. Absorbance spectra were obtained experimentally and computationally with an absorbance band in the range of 450-600 nm that has been attributed to Bi(V). The ingrowth and decay of Bi(V) in solution was also studied as a function of mass of solid NaBiO3 present, acidity, and temperature. The activation energies of dissolution and decomposition were calculated to be 39 ± 4 and 61 ± 6 kJ/mol, respectively. These results indicate that dissolution of NaBiO3 into the respective Na+ and BiO3-occurs prior to undergoing reduction, a process which conventionally has been believed to occur in the reverse order.

Early Liquid and Gas Phase Hypergolic Reactions between Monomethylhydrazine and Nitrogen Tetroxide or Red Fuming Nitric Acid

ABSTRACT Monomethylhydrazine (MMH) fuel and nitrogen tetroxide (NTO)-based oxidizers embody the state of the art for hypergolic propellants. Despite their wide use, a detailed understanding of the full reaction chemistry between MMH and NTO, from early liquid phase reactions to ignition in the gas phase, is lacking. The gas phase reactions are relatively well understood with several spectroscopic techniques well suited to probe gaseous reaction zones and numerous computational chemistry studies supporting the experimental data. The present paper focuses on the early liquid phase reactions with a method devoted to the determination of Arrhenius preexponential factors and activation energies for global, single-step liquid phase chemical reaction models for MMH-NTO and MMH-red fuming nitric acid (RFNA) systems. Using a temperature and atmosphere controlled droplet contact chamber, the liquid phase induction delay times of MMH-RFNA and MMH-NTO were examined by capturing drop on drop tests at frame rates from 100,000 to 500,000 fps. Results indicate induction delays on the order of 30–100 microseconds and 10–40 microseconds for MMH-RFNA and MMH-NTO, respectively, and distinct reaction rate parameters for both pairs of propellants.

Drop formation at nozzles submerged in quiescent continuous phase: an experimental study with TBP-dodecane and nitric acid system

Solvent extraction is an important process in the nuclear fuel cycle. Tributyl phosphate (TBP) diluted with dodecane is commonly used as a solvent for extracting heavy metals from nitric acid medium. Studies on hydrodynamics of a single drop, which is the smallest mass transfer entity, are required for better understanding of the complex mass transfer and phase separation phenomena that occur in extraction equipment. In this study, drop formation at nozzles is studied using 30% TBP-dodecane as the dispersed phase and dilute nitric acid as the quiescent continuous phase. Experiments are carried out to determine the drop diameter, jetting velocity, drop detachment height and drop detachment time for various dispersed phase velocities, nozzle diameters (1.91, 3.04, and 4.88 mm), and nitric acid concentrations (0.01, 1, 3 N). Drop formation is captured using high-speed imaging, which enables quantification of drop size, onset of jetting, drop detachment height, and drop detachment time. Experimental data are used to propose correlations for predicting drop diameter and minimum jetting velocity. The correlations are found to be very accurate with average absolute relative errors being 5.23 and 2.97%, respectively.

Specific features of decomposition of hydroxamic acids in two-phase nitric acid systems with alcohols and TBP, as applied to 99Mo stripping

Hydrolysis is the prevalent mechanism of decomposition of benzo- and caprinohydroxamic acids (HAs) in nitric and perchloric acid solutions and in the equilibrium organic phase based on heptanol, decanol, and 30% TBP in С13 paraffin diluent. In the nitric acid system with alcohols, HAs undergo autocatalytic oxidation at temperatures raised over 50°С. In the case of BHA, the process occurs in both phases taken separately and on their mixing. In the case of caprinohydroxamic acid poorly soluble in HNO3 solutions, the autocatalytic process occurs only at 70–80°С on mixing the phases; it tends to fade as the phase ratio n = О/A is increased from 1 to 10. This trend determines the conditions for Mo stripping in this system. In the practice of the 99Mo production, the stripping efficiency can be increased by repeated contact with the addition of non-salt complexing agents (H2O2, H2C2O4, CH3CONHOH) into the system.

Electrochemistry and Spectroelectrochemistry of the Pu (III/IV) and (IV/VI) Couples in Nitric Acid Systems

AbstractThe solution chemistry of Pu in nitric acid is explored via electrochemistry and spectroelectrochemistry. By utilizing and comparing these techniques, an improved understanding of Pu behavior and its dependence on nitric acid concentration can be achieved. Here the Pu (III/IV) couple is characterized using cyclic voltammetry, square wave voltammetry, and a spectroelectrochemical Nernst step. Results indicate the formal reduction potential of the couple shifts negative with increasing acid concentration and reversible electrochemistry is no longer attainable above 6 M HNO3. Spectroelectrochemistry is also used to explore the irreversible oxidation of Pu(IV) to Pu(VI) and shine light on the mechanism and acid dependence of the redox reaction.

The complex reaction kinetics of neptunium including redox and extraction process in 30% TBP—nitric acid system

In order to understand the complex and dynamic neptunium process chemistry in the TBP-HNO3 system, the kinetics involved reversible redox reaction and extraction mass transfer was investigated. The results indicates that the mass transfer rate of Np(VI) is much faster than the redox reaction in aqueous solution. The concentrations of nitric acid and nitrous acid not only can change the Np(V) oxidation reaction and Np(VI) reduction reaction rate, but also can ultimately determine the distribution of neptunium extraction equilibrium. The variety of temperature can only influence the extraction equilibrium time, but cannot alter the equilibrium state of neptunium.