Aqueous Solutions Of Nitrate Salts Research Articles

The role of Alkali dopants on the Oil Methanolysis Behavior of Lime Catalyst: Activity & Stability

ABSTRACT Heterogeneous basic catalysts, namely calcium oxide, are referred to as promising catalysts for biodiesel (FAME, fatty acid methyl esters) production since they can be easily separated from the reaction medium allowing them to operate in a continuous mode. Despite the relatively high catalytic activity of calcium catalysts, they present slower alcoholysis rates than homogeneous conventional catalysts (sodium or potassium methanoate). In order to improve the catalytic activity, CaO-based catalysts, modified with alkali elements (Li, Cs, Sr, and Mg) were prepared. Dopant element contents of 10% and 30%, as weight basis (5–50% molar), were introduced by wet impregnation using aqueous solutions of nitrate salts. The effect of calcination temperature (575°C and 800°C) on both activity and stability was studied. All the prepared catalysts, raw and alkali modified, showed pKa<15.0 when characterized by Hammett indicators in methanolic solution. Such basicity is characteristic of Ca hydroxide, thus indicating that the catalysts surfaces were covered with Ca-OH species. FAME yield, in soybean oil methanolysis, higher than 96% was obtained for the first batch reaction for all the tested catalysts showing that alkali dopants have an almost nihil effect on the catalysts performances. The deactivation tests performed with catalysts without intermediate reactivation showed that calcination temperature plays a major role in stability as it enhances the formation of calcium diglyceroxide. The presence of Ca hydroxide in fresh catalysts appears to be responsible for fast deactivation. The dopant elements prompt the catalysts deactivation. Catalysts calcined at higher temperatures showed slower deactivation, which can be due to the formation of larger particles, thus reducing the contact with the formed glycerin. Alkali dopants enhanced the CaO sintering for the highest calcination temperature. Calcium diglyceroxide formed during the reaction is responsible for deactivating the catalyst, due to leaching, and such effect is prompted by alkali dopants.

Effect of pH on Total Volume Membrane Charge Density in the Nanofiltration of Aqueous Solutions of Nitrate Salts of Heavy Metals.

The separation efficiencies of aqueous solutions containing nitric salts of Zn, Cu, Fe or Pb at various pH in process of nanofiltration have been investigated experimentally. These results were used to obtain the total volume membrane charge densities, through mathematical modelling based on the Donnan–Steric partitioning Model. The experimentally obtained retention values of individual heavy metal ions varied between 36% (Zn2+ at pH = 2), 57% (Pb2+ at pH = 2), 80% (Fe3+ at pH = 9), and up to 97% (Cu2+ at pH = 9). The mathematical modelling allowed for fitting the total volume membrane charge density (Xd), which yielded values ranging from −451.90 to +900.16 mol/m3 for different non-symmetric ions. This study presents the application of nanofiltration (NF) modelling, including a consideration of each ion present in the NF system—even those originating from solutions used to adjust the pH values of the feed.

Phase development in the metastable solid solutions of ZrO2-YO1.5 system

Metastable solid solutions of ZrO2-YO1.5 system (from 0 to 100 mol%) were prepared by crystallization of the amorphous precursors, coprecipitated from aqueous solutions of nitrate salts, using two synthesis routes: hydrothermal treatment at 150 °C for 24 h and annealing in the air atmosphere for 2 h at temperatures between 400 and 1200 °C. Thermal behavior of the amorphous precursors were followed by differential scanning calorimetry (DSC), structural analysis of the crystallization product was performed by X-ray powder diffraction (XRPD) and Raman spectroscopy, and the morphology of the crystalline grains was determined by the scanning electron microscope (FE-SEM). It was found that the crystallization temperature of ZrO2-type solid solutions increase with an increase in the YO1.5 content, from 487 °C (0 mol% of YO1.5) to 516 °C (20 mol% of YO1.5). Comparison of the obtained results with the results obtained for mixed oxides of zirconium with different trivalent dopants indicates that the crystallization temperature rises with the increase of dopand content and the difference between the ionic radius of the zirconium and the doped cation. The results of Rietveld refinements show that, regardless of the significant differences in the crystallite size and the morphology of the products obtained by two different synthesis routes, the phase composition and the unit cell parameters of the solid solutions obtained are very similar and depend mostly on the Zr/Y ratio. Crystallization products with YO1.5 content ≥5 mol% contain only one type of solid solution structurally closely related to tetragonal ZrO2 (from 5 to 15 mol% of YO1.5), cubic ZrO2 (from 15 to more than 60 mol% of YO1.5) and cubic Y2O3 (from 70 to 100 mol% of YO1.5). The unit-cell volume of the ZrO2- and Y2O3-type solid solutions increases linearly with the increase in the fraction of the yttrium. This linear dependence continued even after the transitions from ZrO2-type to Y2O3-type lattice.

Preliminary studies on the growth, tolerance and phytoremediation ability of sugarbeet (Beta vulgaris L.) grown on heavy metal contaminated soil

Sugarbeet (Beta vulgaris L.) was tested in a greenhouse pot experiment to evaluate its growth, tolerance ability and remediation potential to soils contaminated with cadmium (Cd) and nickel (Ni). Sugarbeet seeds were pre-germinated and four weeks after sowing the seedlings were transplanted to 36 pots. They were left to grow for 12 weeks and then aqueous solutions of nitrate salts of Cd and Ni were added to the soil. The applied treatments were: only Cd(NO3)2.4H2O addition in quantities (g) of Cd0:0, Cd0.5:0.5, Cd5:5, and Cd10:10; only Ni(NO3)2.4H2O addition in quantities (g) of Ni0:0, Ni1:1, Ni10:10, and Ni20:20; a combination of both salts in quantities (g) of Cd0+Ni0: 0+0, Cd0.25+Ni0.5: 0.25+0.5, Cd2.5+Ni5: 2.5+5, Cd5+Ni10: 5+10. At the end of the experiment, the determined DTPA-extractable metal concentrations in soil were up to 225.8mg Cd kg−1 and 75.4mg Ni kg−1. Under the Cd treatment, plant growth remained unaffected, with the exception of the leaves’ number, which differed significantly among control (Cd0) and highly (Cd10) treated plants on the last measurement date. Nickel affected sugarbeets growth and Ni20 was lethal to the plants. Under the combined Cd and Ni treatment, the toxicity symptoms were milder than in Ni treatment and only the Cd5+Ni10 treated plants were affected. The higher accumulation rate of Cd and Ni was recorded in the above-ground biomass, with beets also experiencing cadmium and nickel accumulation. Under Cd10 treatment, metal content reached 92.1mgkg−1 in the aboveground biomass and 14.3mgkg−1 in beets, while Ni concentrations under Ni10 treatment were up to 283.3mgkg−1 and 45.9mgkg−1 respectively. Under the combined Cd and Ni treatments, Cd concentrations were up to 172.5 and 76.7mgkg−1 in shoots and beets, respectively, while Ni was up to 467.8 and 289.7mgkg−1, respectively. Metal accumulation (mg per pot) in the single experiments followed the pattern Cd>Ni, mostly due to the higher biomass production in the Cd pots and the higher Cd mobilized content in the soil. In the combined Cd and Ni contamination, Ni accumulation was higher than the Cd accumulation, reflecting a preference by sugarbeet to absorb an ion with lower radius and higher electronegativity. Higher modified translocation factors (mTFs) were obtained for Ni, in the single experiments. In the combined experiment, the mTFs was reduced for both metals due to the combined accumulation of Ni and Cd. Sugarbeet can be considered an interesting candidate for Cd phytoextraction, favored by the biomass produced and accumulation observed but further studies should be conducted in order to evaluate the effect of the soil contamination on the bioethanol yield and quality.

Crystallization of interphase droplets in emulsion explosive matrices

ABSTRACTThe instability of emulsion explosive matrices is mainly due to the crystallization of interphases as oversaturated aqueous solutions of nitrate salts. The principal features of crystallization for this type of emulsion have been previously studied; however, there is no consensus regarding the mechanism of crystallization for an emulsion explosive matrix. This study is devoted to the investigation of the crystallization behavior of interphase droplets. By monitoring the mass change of emulsions during their aging process, it was found that the mass of the emulsions remains almost constant and that water still completely existed in the emulsion system after crystallization of the interphase droplets. The ammonium nitrate (NH4NO3) crystals in the emulsion explosive matrices were then separated successfully using a simple method. The thermal behavior of pure NH4NO3 and crystals in the emulsion explosive matrices was studied by differential scanning calorimetry-thermogravimetric analysis (DSC-TG) at a heating rate of 10 K/min. The experimental results show that the thermal behavior of the crystals in the emulsions was exactly the same as for pure NH4NO3, meaning that only NH4NO3 crystallized from the emulsion explosive matrices with no water crystals. Thus, it could be concluded that after crystallization of the dispersed drops in the emulsion explosive matrices, pure NH4NO3 crystals and new smaller droplets were produced.

Photocatalytic performance of fine particles of Cr doped magnesium ferrites prepared by sol–gel combustion route

The present wet chemical route overcome all drawbacks of conventional processes and produce ultra-fine, homogeneous reproducible ferrite powders using aqueous solutions of nitrate salts of constituent ions. The study is investigated for the application of system MgFe2−x Cr x O4 (0.0 ≤ x ≤ 1.0) in photo decoloration and degradation of MO, MR and CR dyes. The precipitation methods always have the disadvantage that the stoichiometry of the precipitate may not be exact if one or more ions are left in solution. The sol–gel route overcomes this because the reactants never precipitate out. The basic aim of this study is photocatalytic performance of synthesized compounds for effective degradation of dyes under severe conditions.

Synthesis of BiFeO3 by Wet Chemical Methods

The synthesis of phase‐pure BiFeO3 has been demonstrated by a chemical synthesis route as well as the solid‐state method at 825°C. Polymeric BiFeO3 precursors were obtained from aqueous solutions of nitrate salts and carboxylic acids with and without ethylene glycol added as a polymerization agent. The polymeric precursors were shown to decompose above 200°C with successive nucleation and growth of BiFeO3 above 400°C. The phase purity of the product was shown to depend on the type of carboxylic acid used, and tartaric, malic, and maleic acids resulted in nanocrystalline phase‐pure BiFeO3. The unit cell and Néel temperature of the bulk materials obtained by the two methods were in accord with previous reports.

Enthalpies of Transfer of Amino Acids from Water to Aqueous Solutions of Alkali Metal Nitrates

Enthalpies of solution of glycine, l-alanine, and l-serine in water and aqueous solutions of LiNO3, NaNO3, and KNO3 were measured at 298.15 K. Enthalpies of transfer (ΔtrH) of amino acids from water to aqueous solutions of nitrate salts were derived. The effect of the ion type, concentration, and structure of amino acids on the magnitude of the transfer enthalpies are discussed in terms of the electrostatic interaction and the structural hydration interaction model.

Calculation of solid-liquid equilibria in aqueous solutions of nitrate salts using an extended UNIQUAC equation

An extended UNIQUAC-Debye-Hückel model is used to predict solid-liquid equilibria for aqueous solutions of nitrate salts with the cations K +, Mg 2+ and Ca 2+. In addition to a model for activity coefficients in mixed electrolyte solutions, the method requires knowledge of the solubility products of all possible solid phases. Furthermore, some ternary solid-liquid equilibrium data are required. It is shown that the extended UNIQUAC equation can be applied to the calculation of solid-liquid equilibria in the K +-Mg 2+-Ca 2+-NO 3 −-H 2O system with good results. A new algorithm for calculation of solid-liquid equilibrium in ionic solutions has been proposed. The number and amount of phases in equilibrium are found by minimization of the total Gibbs function of the system.

The Effect of Surface Additives on the Oxidation of Chromia-Forming Alloys

Abstract The influence of the surface application of active elements on the composition, morphology, adherence, and growth rate of oxide scales formed during high temperature exposure has been investigated. The active elements were applied as aqueous solutions of nitrate salts that were subsequently transformed into oxide. The active elements used were: Y, Ce, La, Hf, Ca, and Zr. The chromia-forming substrates used were AISI 304 and 310 stainless steels and IN 738, a nickel base alloy. To determine the effect of the minor alloying elements in stainless steels on the surface doping effect, Y was applied to three alloy modifications of AISI 304. The effect of the presence or absence of Mn and Si in the alloy on high temperature corrosion behavior was determined. Several different application techniques were used to determine which technique was most beneficial to the behavior of the oxide barrier scale. The application of Y, Ce, and La was found to enhance the oxidation resistance of the commercial stainles...

Ion–ion–solvent interactions in solution. Part 5.—Influence of added halide, change in temperature and solvent deuteration on ion association in aqueous solutions of nitrate salts

Band-component analysis of the band due to symmetrical stretching of the nitrate ion in aqueous solutions has been used to study association equilibria. Variation of anion composition at constant ionic strength indicates that the association equilibria are weakly dependent on the nature and concentration of counter-ions. Variation of ionic strength at constant anion concentration produced large changes in the associated species. Association was found to be dependent on both the competitive association equilibria with other anions and of the structural disturbance of the solution. The measurement of the concentration of associated species as a function of temperature in solutions of NaNO3 showed that the formation of both solvent-separated ion pairs and contact ion pairs is favoured by a reduction in temperature. Values of the enthalpy change associated with the equilibria Na+(aq)+ NO–3(aq) [graphic omitted] Na+· H2O · NO–3(aq) [graphic omitted] Na+· NO–3(aq) were found to be ΔH1=–42.2 kJ mol–1 and ΔH2=–64.56 kJ mol–1. In a comparison of association equilibria in H2O and D2O solutions of LiNO3, NaNO3 and KNO3 the association equilibria were all altered in a way compatible with the solvent D2O having weaker hydrogen bonding and aquating properties than H2O.