Sodium Nitrate Solutions Research Articles

Synthesis and Properties of Calix[4]arene‐bis[4‐(2‐ethylhexyl)benzo‐crown‐6], A Cesium Extractant with Improved Solubility

The new cesium‐selective macrocycle calix[4]arene‐bis[4‐(2‐ethylhexyl) benzo‐crown‐6] (“BEHBCalixC6”) has been found to have improved solubility in a modified alkane diluent over calix[4]arene‐bis(4‐tert‐octylbenzo‐crown‐6) (“BOBCalixC6”). The synthesis of this new calixcrown extractant, together with its solubility and extraction properties, is described in this report. The solubility, cesium extraction, and potassium loading behavior are compared with those of BOBCalixC6, the macrocycle currently employed in the caustic‐side solvent extraction (CSSX) process for extracting cesium from alkaline nitrate solutions such as high‐level nuclear waste. Replacement of the tert‐octyl alkyl chains on the benzo‐crown portion of the calixcrown by 2‐ethylhexyl chains improves the equilibrium solubility of the free calixcrown in aliphatic diluents while not affecting the cesium extraction strength. Equilibrium concentrations of BEHBCalixC6 in Isopar L diluent modified with 0.5 M 1‐(2,2,3,3‐tetrafluoropropoxy)‐3‐(4‐sec‐butylphenoxy)‐2‐propanol (Cs‐7SB) over the course of 41 weeks of gentle agitation at 25°C maintained the initial concentration of 57 ± 2 mM, with no evidence of precipitation or third‐phase formation. In contrast, 57 ± 2 mM solutions of BOBCalixC6 prepared using sonication were not stable, with precipitation occurring to afford an equilibrium concentration of only 6.7 ± 0.2 mM after 41 weeks. Third‐phase tests showed that BEHBCalixC6 resists third‐phase formation as well as, or better than, BOBCalixC6. With increasing potassium loading from an alkaline sodium nitrate solution, both calixcrowns at 20 mM in modified Isopar L exhibited comparable onset of third‐phase formation, gauging by the decreasing mass balance in cesium extraction from the same solutions. However, the BEHBCalixC6 solvent exhibited no visible indications of third‐phase formation until the aqueous potassium concentration reached 0.75 M, whereas the BOBCalixC6 suffered visible third‐phase formation when the aqueous potassium nitrate concentration reached 0.25 M. Calixcrowns with higher solubility in alkane diluents may find application in cesium extraction from waste matrices containing moderate (≥0.2 M) quantities of potassium, such as that stored at the US Department of Energy's Hanford Site, where higher concentrations of the calixcrown extractant may be required to obtain practical cesium distribution coefficients for process flowsheets.

Anodic polarization behavior of low-carbon steel in concentrated sodium hydroxide and sodium nitrate solutions

High-level radioactive wastes, primarily consisting of concentrated sodium hydroxide (NaOH) and sodium nitrate (NaNO 3) solutions, are stored in large underground storage tanks made of low-carbon steel. The anodic polarization behavior of low-carbon steel in concentrated solutions of 10 M NaOH and various concentrations of NaNO 3 (0.01–2.0 M) was determined in order to predict the caustic stress corrosion cracking (CSCC) susceptibility of the tanks. The active–passive transition peak exhibited during anodic polarization of low-carbon steel in 10 M NaOH, typically associated with CSCC, at −0.25 and −0.75 V SCE, is still present at the lower and higher concentrations of nitrate. However, there is a mid-range of nitrate concentrations (0.5–1 M) within which the peak is suppressed by the strongly oxidizing nitrate in the presence of oxygen, a cathodic depolarizer. Temperature also affects the magnitude of this mid-range of nitrate concentrations where CSCC is seen to be electrochemically prevented. The data suggest that the oxygen solubility at the relatively low temperatures tested (<95 °C) controls the preference of the cathodic reaction, i.e. oxygen reduction versus nitrate reduction. When oxygen reduction is the preferred cathodic reaction, E corr is driven more noble than the active–passive transition peak.

Inhibition of steel corrosion by calcium benzoate adsorption in nitrate solutions

The inhibitive properties of calcium benzoate for steel corrosion were studied in sodium nitrate solutions at room temperature. Corrosion parameters of the steel/nitrate and steel/benzoate + nitrate interfaces were obtained from polarisation curves. Adsorption parameters of benzoate on steel in sodium nitrate solutions were determined through changes in the degree of surface coverage by the inhibitor, as a function of concentration, time and adsorption potential. The effect of chloride on the corrosion inhibition of benzoate was analysed exposing the metal in different chloride solution concentrations.

Passivity and passivity breakdown of a zinc electrode in aerated neutral sodium nitrate solutions

The passivation and pitting corrosion behaviour of a zinc electrode in aerated neutral sodium nitrate solutions was investigated by cyclic voltammetry and chronopotentiometry techniques, complemented by ex situ scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) examinations of the electrode surface. Measurements were conducted under different experimental conditions. The potentiodynamic anodic polarization curves do not exhibit active dissolution region due to spontaneous passivation. The passivity is due to the presence of thin film of ZnO on the anode surface. The passive region is followed by pitting corrosion as a result of breakdown of the passive film. SEM images confirmed the existence of pits on the electrode surface. The breakdown potential decreases with an increase in NO 3 − concentration and temperature, but increases with increasing potential scan rate. Addition of SO 4 2− ions to the nitrate solution accelerates pitting corrosion, while addition of WO 4 2− and MoO 4 2− ions inhibits pitting corrosion. The chronopotentiometry measurements show that the incubation time for pitting initiation decreases with increasing NO 3 − concentration, temperature and applied anodic current density. Addition of SO 4 2− ions decreases the rate of passive film growth and the incubation time, while the reverse changes produced by addition of either WO 4 2− or MoO 4 2− ions.

Failure analysis of high-level radioactive waste tank purge ventilation vent pipe

High-level radioactive wastes generated during the processing of nuclear materials are stored in large underground storage tanks made of low-carbon steel. The wastes consist primarily of concentrated solutions of sodium nitrate (NaNO3) and sodium hydroxide (NaOH). Each of the tanks is equipped with a purge ventilation system designed to continuously remove hydrogen gas and vapors from the waste tanks while preventing the release of radionuclides to the atmosphere. Several intergranular cracks were discovered in the vent pipe of the purge ventilation system of a particular high-level waste tank. The vent pipe, fabricated from galvanized steel sheet, was connected to the final exhaust fan downstream of high-efficiency particulate air (HEPA) filters. The failure analysis investigation concluded that nitrate-induced stress-corrosion cracking (SCC) was the cause of the failure.

Inhibition of steel corrosion by calcium benzoate adsorption in nitrate solutions: theoretical and experimental approaches.

The inhibitive effects of calcium benzoate on steel corrosion were studied in sodium nitrate solutions at room temperature. Corrosion parameters of the steel/nitrate and steel/benzoate + nitrate interfaces were obtained from polarization curves. Adsorption parameters of benzoate on steel in sodium nitrate solutions were determined through changes in the degree of surface coverage by the inhibitor, as a function of concentration, time, and adsorption potential. The most likely adsorption configuration of benzoate on iron was envisaged with the help of semiempirical calculations such as extended Hückel calculations. A two-dimensional flat configuration was involving at least two metal atoms, one interacting with the phenolic group and the other with the carboxylate moiety. The effect of chloride on the corrosion inhibition of benzoate was analyzed by exposing the metal to different chloride solution concentrations, from which corrosion parameters were calculated and compared with those in nitrate solutions.

Structural Features of Ion Hydration in Sodium Nitrate and Thiosulfate

The features of formation of hydration spheres around electrolyte ions in aqueous solutions of sodium nitrate and thiosulfate in a wide concentration range (from 2 to 42 wt %) at temperatures from 278.15 to 318.15 K were determined from the isoentropy compressibility data. The structural characteristics of the solute hydration complexes were determined. The hydration numbers decrease with increasing concentration and are independent of temperature. Na2S2O3 has the highest hydration number at infinite dilution (h 0) and is characterized by the lowest molar isoentropy compressibility of water in the hydration spheres of the ions (βS,1hV1h). Sodium thiosulfate, compared to sodium nitrate, interacts with water stronger, and its aqueous solutions show a greater degree of ordering.

Application of A Monte Carlo Approach to Surface Complexation Modelling

AbstractA Monte Carlo-based approach has been adopted for development of a chemical thermodynamic model to describe the goethite surface in contact with sodium nitrate solutions. The technique involves the calculation of the goethite surface properties for the chemical conditions corresponding to each experimental data point. The representation of the surface was based on a set of model parameters, each of which was either fixed or was randomly sampled from a specified range of values. Thousands of such model representations were generated for different selected sets of parameter values with the use of the standard geochemical speciation computer program, HARPHRQ. The method allowed many combinations of parameter values to be sampled that might not be achieved with a simple least-squares fitting approach. It also allowed the dependence of the quality of fit on each parameter to be analysed. The Monte Carlo approach is most appropriate in the development of complex models involving the fitting of several datasets with several fitting parameters.Introduction of selenate surface complexes allowed the model to be extended to represent selenate ion sorption, selenium being an important radioelement in evaluation of the long-term safety of ILW disposal. The sorption model gave good agreement with a wide range of experimental sorption datasets for selenate.

Uptake of radionuclides on antimony silicate

The uptake of fission products 137Cs, 85Sr, 57Co, onto an antimony silicate, and its Na, K, Ca ion-exchanged forms have been studied. Distribution coefficients have been determined as a function of the concentrations of sodium, potassium and calcium nitrate solutions (0.01, 0.1 and 1M). Plots of log distribution coefficients against concentrations enabled the elucidation of exchange mechanisms in some cases. Potassium had the least, and calcium the most effect on isotope uptake when present as macro ions. The presence of sodium promoted hydrolysis that also affected the exchange selectivity.

Efficacy of Electrolyzed Water As a Primary Cleaning Agent

Alkaline (AIEW) and acidic electrolyzed water (AcEW) were prepared by the electrolysis of a dilute sodium nitrate solution. The efficacy of AIEW (pH 11.5) in removing the gelatin deposited on stainless steel particles was compared with that of warm deionized water (DIW; pH 5.7) at various temperatures of 20 to 80°C. The efficiency of the DIW cleaning increased with increasing temperatures from 20 to 70°C, whereas it decreased to some extent at 80°C. On the other hand, the efficiency of AIEW cleaning increased with increasing temperatures up to 50°C, above which it decreased gradually. AIEW cleaning was shown to be by far more effective in removing gelatin than warm DIW cleaning, and its optimum temperature was 50°C. AcEW cleaning removed calcium hydrogenphosphate deposited on stainless steel particles, depending on the solution pH, and resulted in the modification of the surface charge of stainless steel particles, due to the oxidizing action of nitrate in AcEW.

Solidification and compositional convection of a ternary alloy

We present the results of an experimental study on the solidification of aqueous solutions of potassium nitrate and sodium nitrate cooled from below. Upon cooling, two distinct mushy layers form, primary and cotectic, separated by an approximately planar horizontal interface. A density reversal between the two mushes causes the residual liquid in the upper, primary mush to be more buoyant than the melt overlying it, while the cotectic mush is compositionally stable. The unstable concentration gradient between the melt and primary mush causes convection that keeps the melt well-mixed and reduces the concentration gradient to zero after a finite time. At this point, the cotectic mush overtakes the primary mush and a transition from a convective regime to a diffusive regime occurs. Our measurements show that this transition is rapid and alters the growth rate of the single (cotectic) mush layer that remains. Concentration measurements taken from within the melt during convection and from within the mush during the diffusive regime show good agreement with the concentration evolution predicted by use of the equilibrium ternary phase diagram. We describe a global conservation model for solidification of a ternary alloy in this regime. Predictions from our model forced with empirical data for the heat and solute fluxes are in good agreement with the measured data for the interface positions of the two mushy layers. We also discuss how solid fractions vary with different melt concentrations in a non-convecting alloy and examine the influence of vertical solute transport in the convecting case. The identification of a density reversal in the solidification of a ternary alloy begins to address the complexities in solidification processes of multi-component alloys.

An electrochemical study of the oxidation of 1,3,5-Tris[4-[(3-methylphenyl)phenylamino]phenyl]benzene

An investigation into the oxidative electrochemistry of 1,3,5-Tris[4-[(3-methylphenyl)phenylamino]phenyl]benzene (TMPB) is described. In particular, the heterogeneous electron-transfer kinetics in N, N-dimethylformamide (DMF) and dichloromethane (DCM) are studied using the high-speed microband channel electrode. Experiments to investigate the standard electrochemical rate constants, k 0, transfer coefficients, α, and formal potentials, E f 0, of the observable oxidations of TMPB in both DMF and DCM solutions containing 0.10 M tetrabutylammonium perchlorate (TBAP) are reported for 12.5 μm platinum microband electrodes using a range of linear flow velocities from 12 to 25 m s −1. The measured values of k 0 for the two measurable oxidations in DMF are 1.03 ± 0.41 and 1.02 ± 0.20 cm s −1, and for the three oxidations in DCM are 0.44 ± 0.04, 0.17 ± 0.03 and 0.08 ± 0.02 cm s −1, respectively. The values of α for these oxidations in DMF are 0.48 ± 0.06 and 0.52 ± 0.02, and in DCM are 0.52 ± 0.02, 0.62 ± 0.03 and 0.53 ± 0.07, respectively. The respective formal oxidation potentials (all measured vs Ag) are 0.533 ± 0.002 and 0.766 ± 0.003 V in DMF, and 0.161 ± 0.002, 0.495 ± 0.002 and 1.128 ± 0.004 V in DCM. The presence of the monocation radical in DCM is confirmed by ESR measurement. Experiments are also presented to explore the voltammetry of TMPB in microdroplets of toluene and also in the solid-phase, when in contact with aqueous solutions of sodium fluoride, perchlorate, nitrate and sulphate. It was found that, when TMPB is dissolved in a toluene microdroplet, anion insertion accompanies the first oxidation for the case of perchlorate and nitrate, with anion-facilitated dissolution occurring for sulphate and fluoride. More complex reactions occur at more positive potentials. In the solid-phase, however, slow anion-facilitated dissolution still occurs for fluoride and sulphate, and rapid direct dissolution takes place in the case of perchlorate.

Raman study of aqueous sodium nitrate, activated by the high-voltage pulsed electric discharge

Raman spectra of a saturated aqueous solution of sodium nitrate (NaNO 3/H 2O) in the region of the totally symmetric vibration ν 1( A) of the NO 3 − anion has been studied. The high-voltage pulsed electric discharge effect (HPED activation) on the molecular relaxation in NaNO 3/H 2O has been investigated. The temperature dependences of the width and frequency of the corresponding spectral line are examined. The transition of NaNO 3/H 2O from the normal state to the activated state under HPED effect is observed. The activated state of NaNO 3/H 2O is nonequilibrium and metastable.

Experimental Determination and Prediction of Gas Solubility Data for CO2 + H2O Mixtures Containing NaNO3 or KNO3

In a continuation of earlier investigations, gas solubility data of carbon dioxide (CO2) in aqueous sodium and potassium nitrate solutions (NaNO3, KNO3) were measured using the static synthetic method in a temperature range from 313 to 373 K, for pressures up to 10 MPa and molalities up to 10 mol·kg-1. Additionally, Henry coefficients were derived from these experimental P−x data, and the experimental data were used to fit interaction parameters for an equation of state approach, which consists of a combination of the predictive Soave−Redlich−Kwong (PSRK) group contribution equation of state and the LIFAC method for the prediction of vapor−liquid equilibria in systems with strong electrolytes.

Selectivity of calix[4]arene-bis(benzocrown-6) in the complexation and transport of francium ion.

It is shown for the first time that a representative member of the "cesium-selective" calix[4]arene-crown-6 family exhibits a high affinity for Fr+ ion. In the investigation, the transport of 221Fr+ and Cs+ ions by calix[4]arene-bis(benzocrown-6) from an aqueous sodium nitrate solution into the water-immiscible diluent 1,2-dichloroethane was measured and compared to address the question of selectivity of the calix-crown-6 cavity toward alkali metal ions of increasing size. Selective separation of 221Fr+ from its parent 225Ac and from the matrix Na+ ions was demonstrated. Higher distribution ratios were obtained than those for the Cs+ ion. The extraction equilibria were determined for the case of the Cs+ ion, and the same equilibria were shown to be applicable to the case of Fr+ with inclusion of additional competitive effects.

Nitrates in ice: uptake; dielectric response by the layered capacitor method

Ice columns of 0.20–0.25 m length and 0.038 m diameter were grown in the laboratory from dilute solutions (10–5 to 10–2 N) of potassium, sodium, or ammonium nitrate at a constant freezing rate of 0.002 m h–1 and stirring at 300 rpm. The distribution coefficient was computed at ~0.015 m intervals as the ratio of nitrate concentration in the melted ice and in the liquid phase as a function of interface position. The average distribution coefficients were (2.25 ± 0.55) × 10–4 for the potassium and sodium nitrate, and (6.1 ± 1.4) × 10–3 for the ammonium nitrate samples — about a 27-fold increase. These results are in line with other large anions such as sulfate and methanesulfonate that were previously investigated. The dielectric relaxation spectrum of ice slices (~0.012 m thick and sandwiched between thin fluoroplastic foils) was measured between –1 and –85°C at frequencies from 1 Hz to 100 kHz with a lock-in amplifier technique. First, the ice response was recovered from the (Maxwell–Wagner) layered capacitor. The dielectric relaxation ranges were then separated and their characteristic parameters computed. The complex conductivity (Grant plot) and the conductivity frequency-response plot have been the most useful tools for this purpose. Both (alkali-metal and ammonium nitrate) sample groups exhibit the Debye dispersion of polar molecules so characteristic for ice regardless of impurity content. There is also a dispersion range at lower frequencies, and a static or quasi-static conductivity. In the alkali-metal nitrates the low-frequency dispersion is a prominent space-charge dispersion, and the temperature-dependent interaction between orientational and ionic point defects in the ice lattice leads to the conductivity crossover phenomenon. Ammonium greatly reduces the ionic lattice defects responsible for space charge and static conductivity; there is no crossover. Both the Debye dispersion and the crossover support the concept of co-operative responses by the polar molecules making up the ice substance to physico-chemical stimuli. PACS Nos.: 61.72, 77.22G, 77.22J, 81.30F

Uptake of radionuclides on microporous and layered ion exchange materials

Titanosilicates, layered manganese oxides and an antimonysilicate were tested for their ability to take up the reprocessing spent fuel transuranium isotopes americium-241 and plutonium-236. This was performed in different concentrations of acid, and sodium and calcium nitrate solutions to represent the conditions of nuclear waste treatment. The purpose was to assess the waste types (acidic or low-medium-high-salt) most suited to treatment by these materials. The experiments were carried out by the batch method and the results obtained expressed as distribution coefficients. Variation in the magnitude and mechanism of actinide sorption by the materials was attributed to the differences in the frameworks, physical properties (porosity, crystal size and chemical composition) and surface charges of the ion exchangers. In nitric acid solutions, the H-antimonysilicate proved to be a better sorbent than H-birnessite for both actinide elements. The void space of AM-4 layered titanosilicate material made it appropriate for actinide removal in sodium salt solutions. The differences in selectivity of Ca-antimonysilicate and Ca-birnessite for americium-241 and plutonium-236 in 0.01 M calcium nitrate solution reflected the preference of each material for actinides over calcium ions.

Application of natural phosphate modified with sodium nitrate in the synthesis of chalcones: a soft and clean method

The solid obtained by impregnation of natural phosphate (NP) with a solution of sodium nitrate, followed by calcination at 900 °C, is a strongly basic catalyst that is easily prepared from cheap precursors. The catalytic activity of this solid in the Claisen–Schmidt condensation was studied and high yields were obtained with small amounts of catalyst. The reaction rate depends on the substitution in both benzaldehyde and acetophenone derivatives. The effect of the solvent, as well as the addition of water and ammonium salt, was investigated as well. The catalyst can be easily recovered and efficiently reused.

Fractionation of transgenic corn for recovery of recombinant enzymes

AbstractTwo germ‐separation methods, dry‐milling and density separation by flotation, were evaluated for recovering recombinant β‐glucuronidase (rGUS) that accumulated primarily in the germ of transgenic corn. The dry‐milling process consisted of (i) seed tempering, (ii) degerming with a horizontal‐drum degermer/dehuller, (iii) particle size fractionation with standard sieves, (iv) germ and endosperm separation by roller milling and sifting, and (v) removal of hulls by aspiration. Sieves nos. 5, 6, and 7 retained the majority of germ, and subfractions from these sieves were pooled as a germ‐rich fraction. Mass balances showed that the germ‐rich fraction, which constituted 17% of the total dry‐milled corn weight, contained 49% of rGUS activity and 64% of the total recoverable oil. Germ fractionation by flotation was tested as a proof‐of‐concept method aimed at separating corn fractions based on their difference in specific gravity (sp gr). The process consisted of impact‐grinding of corn kernels followed by density separation using 1.15 or 1.3 specific gravity sodium nitrate solution. The oil‐containing germ fraction floated, whereas the heavier endosperm fraction sedimented. The flotation method was simpler and resulted in higher enzyme recovery, that is, the germ‐rich fraction was 20% (w/w) of the initial corn weight, and accounted for 80% of rGUS activity and 77% of total oil. The sodium nitrate solution did not have an adverse effect on the enzyme activity.

Thermodynamics of ionization of water at temperatures 278.15⩽⩽⩽T / K⩽⩽⩽ 393.15 and at the pressurep = 0.35 MPa: apparent molar volumes and apparent molar heat capacities of aqueous solutions of potassium and sodium nitrates and nitric acid

The apparent molar volumes Vφand apparent molar heat capacitiesCp, φ of aqueous solutions of potassium and sodium nitrate and of nitric acid have been determined over the temperature range 278.15 ⩽T/K⩽ 393.15 and molality range 0.015 ⩽m/ (mol · kg−1) ⩽ 0.5 at the pressure p= 0.35 MPa. Densities of these solutions were measured using a vibrating-tube densimeter (DMA 512, Anton Paar, Austria). The density results were used to calculateVφ for each solution. The massic heat capacities of these same solutions were measured using a twin fixed-cell, differential-output, temperature-scanning calorimeter (NanoDSC model 6100, Calorimetry Sciences Corporation, Spanish Fork, UT, U.S.A.) and these measurements were used to calculate Cp, φfor each solute. The Vφand Cp, φresults were fit to semi-empirical equations by regression. These equations were used to calculate the change in volume ( m, T,ΔrVm ) and the change in heat capacity ( m,T , ΔrCp, m) for ionization of water in KNO3 (aq) and NaNO 3(aq). The ( m, T,ΔrCp, m ) results were integrated to obtain the change in enthalpy ( m, T, ΔrHm), the molality quotient ( m, T, pQw), and change in entropy ( m,T , ΔrSm) for the ionization reaction of water.