High HNO3 Research Articles

ESTIMATION OF NITRIC ACID GAS DRY DEPOSITION IN VIET NAM

This article uses dry deposition calculating method to estimate Nitric acid (HNO3) gas dry deposition and analyze, evaluate trend of HNO3 gas dry deposition in recent years. The results present that HNO3 gas concentration is from 0.02 to 0.83 ppb and Yen Bai site has the highest HNO3 gas emission in 2020 and 2021. High HNO3 gas emission focuses on summer and spring at Northern’s sites. HNO3 gas emission at Southern sites is lower than that of Northern ones. HNO3 gas dry deposition is from 6.63 kg/ha/year to 10.26 kg/ha/year and the highest HNO3 gas dry deposition value is in 2021. Ha Noi site has the highest HNO3 gas dry deposition value in 2019, 2020, and 2022 while Yen Bai site is in 2021 and 2023. HNO3 gas dry deposition value at Southern sites is lower than Northern sites. The highest monthly HNO3 gas dry deposition is from June to August at Yen Bai site in 2021 and May in 2020. Annual average HNO3 gas dry deposition of 2021 is higher than other years. HNO3 gas dry deposition in recent years has an increasing trend.

Precise target capture and the dynamic separation of Sn(IV) in highly acidic media by combining N and P donor covalent organic framework silica-based composite adsorbents

A silica-based adsorbent (P507@COF-TpAzo/SiO2) with nitrogen and phosphorus donors was prepared for industrial separation and recovery of Sn(IV) by in-situ growth of covalent organic framework (COF) on a silica substrate combined with vacuum impregnation. The materials were tested and analyzed by the scanning electron microscope (SEM), X-ray diffraction (XRD) and other characterization techniques, which demonstrated that the adsorbent has an enormous specific surface area, excellent heat resistance, and a regular morphological structure. The static experimental results showed that the adsorbent displayed remarkable selectivity for Sn(IV) in high HCl and HNO3 concentration environments, with excellent kinetics (∼60 min) and outstanding adsorption capacities (60.02 mg/g in 3 M HCl, 92.59 mg/g in 3 M HNO3) in different media at 3 M acidity. Cycle performance testing demonstrated that the adsorbent exhibited excellent stability (cycle times ≥8). Analysis using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) showed that the synergistic adsorption results of N and P were reflected, mainly by the synergistic complexation of P=O and N=N-C. The potential sites for the adsorption of the adsorbent towards Sn(IV) were predicted by density functional theory (DFT) calculations, and the adsorbent demonstrated a more stable binding energy with Sn(IV). Finally, dynamic separation and efficient enrichment (>210) of Sn(IV) in highly acidic wastewater were realized by designing a penetrating column separation process. P507@COF-TpAzo/SiO2 satisfied the requirements of the dynamic adsorption experiments, bridging the research gap of dynamic separation, and provides a new strategy for the industrial removal and recovery of Sn(IV), as well as a way for environmental protection and industrial green production.

Influence of plutonium content in dissolver solutions derived from irradiated fast reactor fuels on plutonium stripping in multistage countercurrent liquid–liquid extraction with acid split flowsheet

ABSTRACT In the acid split flowsheet, the Pu content in the dissolver solution of nuclear fuel has a significant impact on the configuration of flowsheet and the Pu content in the products. The influence of Pu content in dissolver solutions of nuclear fuel on the Pu stripping has been studied. The decontamination performance of Cs as major fission products was assessed, and Cs was decontaminated well in the acid split flowsheet. High HNO3 concentration in the feed solution and at the co-decontamination section was adjusted for the co-recovery of Np with U and Pu, contributing to Np oxidation and the increase in the distribution ratio of Np. The experimental results demonstrate that the Pu content in the U/Pu and U products increased with an increase in the Pu content in the feed solution. The calculated results indicate that the Pu leakage into the U product is suppressed with the Pu stripping solution only at low temperature under our experimental conditions, and Pu is recovered into the U/Pu product efficiently. This study proves that the Pu leakage into the U product is controlled and the acid split flowsheet is flexible with change in the Pu content in the feed solution.

Preparation of crown ether pillared zirconium phosphonate for Strontium Removal

Finding materials with high adsorption capacity and excellent stability for fission products generated in the nuclear fuel cycle remains highly challenging for nuclear wastewater management and contamination remediation. Herein, acid-resistance crown ether pillared zirconium phosphonate (D-AM-ZrP) was prepared by a directly reacting 4-amino-benzo-18 crown 6 phosphonic acid with zirconium other than the conventional complicated intercalation methods. Remarkably, by proper control of the ratio of phosphoric acid to phosphonic acid, the D-AM-ZrP sample with perfect flower-like and well-ordered interlayer structure was obtained, and exhibited the excellent stability under the irradiation and strong acid conditions, which is due to the strong chemical interaction was formed between the crown ether and α-ZrP. More importantly, this D-AM-ZrP exhibited high adsorption capacity and excellent selectivity for removal of Sr2+ from complicated system including high concentrated HNO3 media and competing ions, and the maximum adsorption capacity for Sr2+ (136.42 mg g−1) was 2 times than pure α-ZrP (63.17 mg g−1) at 0.2 mol L−1HNO3 media, which could mainly be attributed to its excellent stability and specific adsorption sites. These excellent properties of D-AM-ZrP were further confirmed by radioactive experiments, and 95% of 90Sr was removal at 0.2 mol L−1HNO3 media, demonstrating that D-AM-ZrP possessed a promising potential for actual application in nuclear wastewater.

Nitric acid dry deposition associated with equilibrium shift of ammonium nitrate above a forest by long-term measurement using relaxed eddy accumulation

The dry deposition process of nitrogen compounds still has considerable uncertainty due to the complex compound behavior in the atmosphere. To enhance understanding of the nitric acid (HNO3) dry deposition process that largely contributes to the total nitrogen deposition, we associate this process with the equilibrium shift of ammonium nitrate (NH4NO3) to HNO3 and ammonia (NH3) near the surface. We obtained the flux of HNO3 and PM2.5 components above a forest in suburban Tokyo using a relaxed eddy accumulation (REA) system incorporating the denuder/filter-pack sampling technique. We conducted continuous samplings on a weekly basis over a long-term period, from October 14, 2016 to October 3, 2018, including leafy and leafless conditions. The measured deposition velocities of fine NO3− particles were significantly (p < 0.05) larger than those of fine SO42− particles and similar to those of HNO3, regardless of the leafy and leafless periods. The larger deposition velocities of fine NO3− particles caused by the equilibrium shift of NH4NO3 were found to be similar to previous measurements at the same site. The measured deposition velocities of HNO3 were low and included many emission cases compared to those of fine NO3− particles. The lower HNO3 deposition velocities were associated with the equilibrium shift of NH4NO3 to the gas phase, causing the suppressed deposition and apparent emission of HNO3, particularly during the leafless period. The emission of HNO3 is possibly due to high HNO3 concentration near the surface, which is attributed to a small removal of the leafless canopy. The turbulence enhanced both the upward and downward fluxes of HNO3. These results will contribute to the better understanding for the dynamics of the nitrogen compounds in the atmosphere and the accurate assessment for the nitrogen deposition.

Modeling of the Competition between Uranyl Nitrate and Nitric Acid upon Extraction with Tri-n-butyl Phosphate.

Uranium is a strategic element and plays an important role in energy resources. A H2O–HNO3–UO2(NO3)2–TBP (tri-n-butyl phosphate)–diluent system is commonly used for uranium separation and purification in liquid–liquid extraction. Uranyl nitrate is promoted by the existence of nitrate at low HNO3 concentrations but is inhibited at high HNO3 concentrations. Considering the competitive extraction between HNO3 and UO2(NO3)2, a generic extraction model is developed. The activities of components in the aqueous phase were estimated using Pitzer models. The thermodynamic equilibrium constants and Pitzer parameters were regressed by experimental data. The resulting model was able to successfully predict uranyl nitrate, nitric acid, and water extraction over a large range of conditions (U, 0–1.8 mol/L; HNO3, 0–10 mol/L; TBP, 5–100 vol %) within average absolute relative deviations of 11.2, 15.7, and 23.8%, respectively. The predicted results show that water and nitric acid were extracted as di-solvates HNO3·(TBP)2·H2O and (TBP)2·2H2O at low nitric acid concentrations, with the formation of mono-solvates HNO3·TBP and HNO3·TBP·H2O as the acid concentration increased. Uranyl nitrate was shown to be rejected from the organic phase as the formation of HNO3·TBP and HNO3·TBP·H2O in acid was extracted at high acid concentrations.

Degradation of sulfamethazine by cerium mediated photoelectrochemical oxidation with hydroxyl radical oxidation effect

A cerium (Ce) mediated photoelectrochemical oxidation (MPEO)/H2O2 system, integrating UV photocatalysis and hydroxyl radical (⋅OH) oxidation, was developed to improve the degradation of sulfamethazine (SMT). SMT is an emerging contaminant with medical toxicity in environmental matrices. In the study of electrolytic production of Ce(IV), the Ce(III)/Ce(IV) redox reaction was found to have good reversibility at high HNO3 concentrations above 0.5 M, due to more cerium ions being trapped by NO3- ions near the anode. In addition, optimum current density of 8 mA cm−2 and reaction temperature of 313 K, for Ce(IV) production, are determined by considering specific energy consumption (SEC) and Ce(IV) percent yield. The MPEO/H2O2 system demonstrates favorable SMT removal efficiencies of 76% and 98%, at treatment times of 60 and 120 min, respectively. This system outperforms the mediated electrochemical oxidation (MEO) and MPEO systems, for SMT degradation. In addition, the kinetics of SMT degradation, using the MPEO/H2O2 system, was found to follow a proposed pseudo-first order model, rather than a pseudo-second order model, and exhibit a higher rate constant than those of the MEO and MPEO systems. Moreover, the concentration of ⋅OH during SMT treatment can be estimated by measuring the concentrations of 4-Hydroxybenzoic acid (4-HBA) and 3,4-Dihydroxybenzoic acid (3,4-DHBA), over time. Our findings reveal that introducing UV irradiation and H2O2 into the MEO system can induce a higher production of ⋅OH in addition to the Ce(IV) ions, thus leading to improved SMT removal efficiency.

ICP-MS method development and validation for determination of trace elemental impurities in caustic potash

ICP-MS method is developed and validated for quantification of trace elemental impurities in caustic potash. Employment of suitable system configuration and optimization of operational parameters was done. Argon Gas Dilution (AGD) kit was employed in this method and metal ions analyzed by employing this method include 208Pb, 111Cd, 107Ag, 88Sr, 64Zn, 63Cu, 59Co, 58Ni, 57Fe, 55Mn and 52Cr. Under normal/routine configuration (without AGD kit), ICP-MS instrument can handle solution having dissolved solids up to 0.2% and is susceptible to compromise with low detection limits. In this work, 1% KOH solution is aspirated post its neutralization by high pure grade HNO3 using AGD kit. It addresses issues of high dissolved solids and high alkalinity. External calibration with internal standards (Sc, Y, Gd) is performed with the matrix of KNO3 since neutralization of KOH by HNO3 forms KNO3. A detailed study of the key features related to the method development such as matrix-matching, accuracy and precision was done.

Direct synthesis of single-phase α-CaSO4·0.5H2O whiskers from waste nitrate solution

Abstract Single-phase α-CaSO4·0.5H2O whiskers were directly synthesized from waste Ca(NO3)2 solution using a hydrothermal method, and HNO3 was synchronously regenerated. The effects of reaction temperature and Ca2+ concentration on the phase composition and morphology of products were determined by X-ray diffraction and optical microscopy. On the basis of the experimental results, the formation diagram of α-CaSO4·0.5H2O was plotted within the range of 5–35 g·L−1 Ca2+ and 115 °C–150 °C. In addition, the conditions of the direct synthesis of α-CaSO4·0.5H2O were determined. Well-crystallized, single-phase α-CaSO4·0.5H2O whiskers with high aspect ratios (length, 1785 μm; diameter, 10.63 μm; aspect ratio, 168) and HNO3 (70.25 g·L−1) were obtained at the optimal conditions of 25 g·L−1 Ca2+ and 125 °C.

Preparation and characterization of tri-n-octylamine microcapsule (TOA-MC) used for selective separation of Re(VII) [chemical analogs of Tc(VII)] in the high level liquid radioactive waste (HLLW)

TOA-MC was developed to act as absorbent for selective separation of 99Tc(VII) from high-level radioactive liquid waste. The uptake (%) of Re(VII) a substitute for Tc(VII) due to similar chemical behavior by TOA-MC normally exceeding 95% in the presence of dilute HNO3 was strongly retained and decreased with higher HNO3 concentration by batch method. The surface morphology, thermal stability and diameter/size distribution of the microcapsules were examined by scanning electron microscopy, thermogravimetric analysis and digital microscope, respectively. The chemical structure was characterized using Fourier transform infrared spectroscopy and 1H nuclear magnetic resonance spectroscopy.

On the consistency of HNO3 and NO2 in the Aleutian High region from the Nimbus 7 LIMS Version 6 data set.

This study uses photochemical calculations along kinematic trajectories in conjunction with Limb Infrared Monitor of the Stratosphere (LIMS) observations to examine the changes in HNO3 and NO2 near 30 hPa in the region of the Aleutian High (AH) during the minor warming event of January 1979. An earlier analysis of Version 5 (V5) LIMS data indicated increases in HNO3 without a corresponding decrease in NO2 in that region and a quasi-wave 2 signature in the zonal distribution of HNO3, unlike the wave 1 signal in ozone and other tracers. Version 6 (V6) LIMS also shows an increase of HNO3 in that region, but NO2 is smaller than from V5. The focus here is to convey that V6 HNO3 and NO2 are of good quality, as shown by a re-examination of their mutual changes in the AH region. Photochemical model calculations initialized with LIMS V6 data show increases of about 2 ppbv in HNO3 over 10 days along trajectories terminating in the AH region on 28 January. Those increases are mainly a result of the nighttime heterogeneous conversion of N2O5 on background stratospheric sulfuric acid aerosols. Changes in the composition of the air parcels depend on the extent of exposure to sunlight and, hence, on the dynamically controlled history of the trajectories. Trajectories that begin in low latitudes and traverse to across the North Pole in a short time lead to the low HNO3 in the region separating the anticyclone from the polar vortex, both of which contain higher HNO3. These findings help to explain the observed seasonal evolution and areal extent of both species. V6 HNO3 and NO2 are suitable, within their errors, for the validation of stratospheric chemistry-climate models.

Continuous measurement of elemental composition of ambient aerosol by induction-coupled plasma mass spectrometry

There is presently no instrumentation that can provide (near) real time information on elemental composition of atmospheric aerosols. We describe an arrangement where air is sampled through a cyclone @30L/min with a 50% cutoff @ ~250nm. The particles deposit into a cup through which deionized water is continuously flowing. High purity HNO3 is added downstream and the mixed stream optionally flows through a quartz photo reactor (185nm, ~90°C, tR ~1.2min) and is aspirated by an induction coupled plasma mass spectrometer (ICP-MS). Comparative batch experiments in which samples were not photodigested at all or thermally digested off-line for an extended period indicated no statistically significant difference in the results. This observation agrees with early theoretical and experimental work. Some 22 elements were quantifiable (S/N > 10) at all times in the aerosol samples collected in our highly urban sampling location; an additional 4 elements were quantifiable at times of construction activity in the general area. Presently attained system limits of detection (LODs) are orders of magnitude higher than the instrumental LOD, both because of the purity of the acid and pump-induced contamination. These aspects can be vastly improved and will need to be improved to determine background concentrations.

Separating lanthanides and actinides from nitric acid solutions by using N,N-di(2-ethylhexyl)-diglycolamic acid (HDEHDGA).

The extraction of Eu(iii), U(vi), and Pu(iv) from 0.1-3 M HNO3 solutions by using N,N-di(2-ethyl-hexyl)-diglycolamic acid (HDEHDGA) is presented. In contrast to common organic acid extractants, such as long-chain carboxylic acids, organophosphorus acids, and derivatives of beta-diketones, losing extractability, HDEHDGA exhibits a strong ability to extract lanthanide and actinide ions from high HNO3 solutions.

Change in the Affinity of Ethylene Glycol Methacrylate Phosphate Monomer and Its Polymer Anchored on a Graphene Oxide Platform toward Uranium(VI) and Plutonium(IV) Ions.

The complexation behavior of the carbonyl and phosphoryl ligating groups bearing ethylene glycol methacrylate phosphate (EGMP) monomer and its polymer fixed on a graphene oxide (GO) platform was studied to understand the coordination ability of segregated EGMP units and polymer chains toward UO2(2+) and Pu(4+) ions. The cross-linked poly(EGMP) gel and EGMP dissolved in solution have a similar affinity toward these ions. UV-initiator induced polymerization was used to graft poly(EGMP) on the GO platform utilizing a double bond of EGMP covalently fixed on it. X-ray photoelectron spectroscopy (XPS) of the GO and GO-EGMP was done to confirm covalent attachment of the EGMP via a -C-O-P- link between GO and EGMP. The extent of poly(EGMP) grafting on GO by thermal analyses was found to be 5.88 wt %. The EGMP units fixed on the graphene oxide platform exhibited a remarkable selectivity toward Pu(4+) ions at high HNO3 conc. where coordination is a dominant mode involved in the sorption of ions. The ratio of distribution coefficients of Pu(IV) to U(VI) (DPu(IV)/DU(VI)) followed a trend as cross-linked poly(EGMP) (0.95) < EGMP in solvent methyl isobutyl ketone (1.3) < GO-poly(EGMP) (25) < GO-EGMP (181); the DPu(IV)/DU(VI) values are given in parentheses. The density functional theory computations have been performed for the complexation of UO2(2+) and Pu(4+) ions with the EGMP molecule anchored on GO in the presence of nitrate ions. This computational modeling suggested that Pu(4+) ion formed a strong coordination complex with phosphoryl and carbonyl ligating groups of the GO-EGMP as compared to UO2(2+) ions. Thus, the nonselective EGMP becomes highly selective to Pu(IV) ions when it interacts as a single unit fixed on a GO platform.

Microphysical properties of synoptic-scale polar stratospheric clouds: in situ measurements of unexpectedly large HNO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;-containing particles in the Arctic vortex

Abstract. In January 2010 and December 2011, synoptic-scale polar stratospheric cloud (PSC) fields were probed during seven flights of the high-altitude research aircraft M-55 Geophysica within the RECONCILE (Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interaction) and the ESSenCe (ESSenCe: ESA Sounder Campaign) projects. Particle size distributions in a diameter range between 0.46 and 40μm were recorded by four different optical in situ instruments. Three of these particle instruments are based on the detection of forward-scattered light by single particles. The fourth instrument is a grayscale optical array imaging probe. Optical particle diameters of up to 35μm were detected with particle number densities and total particle volumes exceeding previous Arctic measurements. Also, gas-phase and particle-bound NOy was measured, as well as water vapor concentrations. The optical characteristics of the clouds were measured by the remote sensing lidar MAL (Miniature Aerosol Lidar) and by the in situ backscatter sonde MAS (Multiwavelength Aerosol Scatterometer), showing the synoptic scale of the encountered PSCs. The particle mode below 2μm in size diameter has been identified as supercooled ternary solution (STS) droplets. The PSC particles in the size range above 2μm in diameter are considered to consist of nitric acid hydrates, and the particles' high HNO3 content was confirmed by the NOy instrument. Assuming a particle composition of nitric acid trihydrate (NAT), the optically measured size distributions result in particle-phase HNO3 mixing ratios exceeding available stratospheric values. Therefore the measurement uncertainties concerning probable overestimations of measured particle sizes and volumes are discussed in detail. We hypothesize that either a strong asphericity or an alternate particle composition (e.g., water ice coated with NAT) could explain our observations. In particular, with respect to the denitrification by sedimentation of large HNO3-containing particles, generally considered to be NAT, our new measurements raise questions concerning composition, shape and nucleation pathways. Answering these would improve the numerical simulation of PSC microphysical processes like cloud particle formation, growth and denitrification, which is necessary for better predictions of future polar ozone losses, especially under changing global climate conditions. Generally, it seems that the occurrence of large NAT particles – sometimes termed "NAT rocks" – are a regular feature of synoptic-scale PSCs in the Arctic.

Variation in isotopologues of atmospheric nitric acid in passively collected samples along an air pollution gradient in southern California

The sources and oxidation pathways of atmospheric nitric acid (HNO3) can be evaluated using the isotopic signatures of oxygen (O) and nitrogen (N). This study evaluated the ability of Nylasorb nylon filters to passively collect unbiased isotopologues of atmospheric HNO3 under controlled and field conditions. Filters contained in passive samplers were exposed in continuous stirred tank reactors (CSTRs) at high (16 μg/m3) and moderate (8 μg/m3) HNO3 concentrations during 1–4 week deployment times. Filters were concurrently exposed at high and low N deposition sites along a gradient in the Sonoran Desert. Filters deployed in CSTRs at moderate HNO3 concentrations for 1–2 weeks had greater variation of δ18O relative to the 3–4 week deployments, while high concentration samples were consistent across weeks. All deployment means were within 2‰ of the source solution. The δ15N of all weekly samples were within 0.5‰ of the source solution. Thus, when deployed for longer than 3 weeks, Nylasorb filters collected an isotopically unbiased sample of atmospheric HNO3. The initial HNO3 samples at the high deposition field sites had higher δ15N and δ18O values than the low deposition sites, suggesting either two independent sources of HNO3 were mixing or that heavier isotopologues of HNO3 were preferentially lost from the gas phase through physical deposition or equilibrium chemical reactions. Subsequent HNO3 samples were subject to summer monsoon conditions leading to variation of isotopic signatures of N and O following 2-source mixing dynamics. Both sites mixed with a source that dominated during the two discrete precipitation events. The high number of lightning strikes near the samplers during the monsoon events suggested that lightning-created HNO3 was one of the dominant mixing sources with an approximate isotopic signature of 21.6‰ and −0.6‰ for δ18O and δ15N respectively. Two-source mixing models suggest that lightning-created HNO3 made up between 40 and 42% of atmospheric HNO3 at the high deposition sites and 59–63% at the low deposition during the 4 week exposure.

Potentially toxic element distribution in soils from the Ag-smelting slag of Kutná Hora (Czech Republic): Descriptive and prediction analyses

The distribution and environmental hazard of potentially toxic elements in the vicinity of a large smelter heap located in the traditional mining town of Kutná Hora, Czech Republic were studied. To understand their occurrence and to predict their mobility and deposition, trends and patterns in PTE distribution were related to soil properties and environmental variables. Slag samples and slag impacted soils were characterized by high 2M HNO3 extractable PTE contents which generally increased with depth, but relatively low plant available fractions; Cd and Mn were the most available elements. Manganese availability was significantly higher in soils under vegetation canopy whereas availability of Cu decreased. Organic matter and pH were identified as significant variables controlling availability of Mn, As and Mn, Zn respectively. Availability of Pb and Cu had significant negative correlation with soil clay content. Mean values of Pb, Mn, Cu, Zn and As from sediment samples exceeded the background value for non-polluted alluvial sediment by 1.8, 1.5, 3.4, 9.8 and 1.3 times respectively. Despite the elevated presence of PTE in river sediments, only Mn and Zn were detected in water samples, but at levels which are not considered hazardous. Included in the paper is a method proposal for quickly and easily identifying threshold values of a chosen soil property which control accumulation of PTE in soil respective of their source. The slag heap at Kutná Hora is a proven source of PTE with evidence of their mobility/transport into the surrounding environment. Although the environment is highly heterogeneous, and the mobility of PTE can be dependent upon pedogenic, geologic, ecological, hydrological and climatic variables, overall the study area was characterized by relatively low availability of PTE, with a limited threat to healthy plant development in the immediate surroundings of the smelter slag heap.

New alkyl-pyridinedicarboxyamides as extractants for separationof trivalent minor actinides from fission products by extraction chromatography

Abstract Four new alkyl-pyridinedicarboxyamides (R-PDA; R = butyl, octyl, decyl, dodecyl) were synthesized and used as extractants for partitioning minor actinides from high level radioactive waste using extraction chromatography. The R-PDAs were successfully impregnated into XAD resins (Amberlite). The prepared adsorbents, R-PDA/XAD, exhibited moderate adsorptions of both Am(III) and Eu(III), and separation between Am(III) and Eu(III), over a high HNO3 concentration range (3–5 M). Deterioration of the prepared adsorbent as a result of contact with HNO3 solution was prevented by using R-PDAs containing longer alkyl groups. The equilibrium data for Eu(III) were analyzed using Langmuir and Freundlich isotherm models. The adsorption of Eu(III) ions onto the R-PDA/XAD was fitted better to the Langmuir isotherm than to the Freundlich isotherm. The maximum adsorption capacity was determined to be 24.2 mg Eu/g (R-PDA/XAD).

Observations of ammonia, nitric acid, and fine particles in a rural gas production region

Continuous measurements of the atmospheric trace gases ammonia (NH3) and nitric acid (HNO3) and of fine particle (PM2.5) ammonium (NH4+), nitrate (NO3−) and sulfate (SO42−) were conducted using a denuder/filter system from December 2006 to December 2011 at Boulder, Wyoming, a region of active gas production. The average five year concentrations of NH3, HNO3, NH4+, NO3− and SO42− were 0.17, 0.19, 0.26, 0.32, and 0.48 μg m−3, respectively. Significant seasonal patterns were observed. The concentration of NH3 was higher in the summer than in other seasons, consistent with increased NH3 emissions and a shift in the ammonium nitrate (NH4NO3) equilibrium toward the gas phase at higher temperatures. High HNO3 concentrations were observed both in the summer and the winter. Elevated wintertime HNO3 production appeared to be due to active local photochemistry in a shallow boundary layer over a reflective, snow-covered surface. PM2.5 NH4+ and SO42− concentrations peaked in summer while NO3− concentrations peaked in winter. Cold winter temperatures drive the NH3–HNO3–NH4NO3 equilibrium toward particulate NH4NO3. A lack of NH3, however, frequently results in substantial residual gas phase HNO3 even under cold winter conditions.

Nitric Acid Concentration Dependence of Dicesium Plutonium(IV) Nitrate Formation during Solution Growth of Uranyl Nitrate Hexahydrate

A crystallization process has been under development for the recovery of U as uranyl nitrate hexahydrate (UNH) crystals. Two experiments, solubility of Cs2Pu(NO3)6 and U crystallization, were performed to evaluate the influence of HNO3 concentration in solution on the precipitation behavior of Cs2Pu(NO3)6. The solubility of Cs2Pu(NO3)6 in a uranyl nitrate solution has been found to decrease with increasing HNO3 concentration in the solution. These experimental results imply that Cs2Pu(NO3)6 is readily formed in high HNO3 concentration solutions. Based on the solubility of Cs2Pu(NO3)6 in uranyl nitrate solutions, U crystallization experiments were performed with a range of HNO3 concentrations in the feed solution. At an HNO3 concentration of 4.5 mol/dm3 in the feed solution, the HNO3 concentration of the mother liquor was 6.5 mol/dm3. The decontamination factor (DF) of Cs for the UNH crystals was 8.61 after crystal washing. In this case, Cs2Pu(NO3)6 precipitated upon cooling of the feed solution and was not separated from the UNH crystals after crystal washing. On the other hand, the DF of Cs was 174 after the UNH crystals were washed when the HNO3 concentration in the feed solution was 3.2 mol/dm3. With a lower HNO3 concentration in the feed solution, nearly all Cs remained in the mother liquor during the U crystallization process. Therefore, to suppress Cs2Pu(NO3)6 precipitation, a lower HNO3 concentration must be maintained in the feed solution.