Transport of AgBr2−, PdBr4 2−, and AuBr4- in an Emulsion Membrane System Using K+-Dicyclohexano-18-crown-6 as Carrier

Abstract

Silver, palladium, and gold have been transported through a 1.5 M KBr/toluene/0.025 M MgS₂O₃ (or Mg(NO₂)₃) emulsion membrane system as AgBr₂ ^?, PdBr₄ ^2? and AuBr₄, respectively, using K⁺-dicyclohexano-18-crown-6(DCl8C6) as carrier. The transport studies are carried out in AgBr₂ ^?, PdBr₄ ^2?, and AuBr₄ ^? single solutions and in AgBr^2?/PdBr₄ ^2?, AgBr^2?/AuBr₄ ^?, and PdBr₄ ^2?/AuBr₄ ^? binary solutions. The presence of DC18C6 in the toluene membrane is found to greatly enhance ion transport. When MgS₂O₃ is in the receiving phase, AuBr_{4 -} is found to transport well even without DC18C6 in the membrane. The transport of AgBr₂ ^?, PdBr₄ ^2?, and AuBr₄ ^? is greater for those systems containing MgS₂O₃ in the receiving phase than for those with Mg(NO₃)². In binary studies with MgS₂O₃ in the receiving phase, PdBr₄ ^2? is transported selectively over AgBr₂ ^? and AuBr₄ ^? is transported selectively over either PdBr₄ ^2? or AgBr₂ ^?.     

Behaviour of nitrate impurity in nickelcadmium cells

The oxidation-reduction behaviour of NO₃ ^?, NO₂ ^?, N₂O₂ ^2?, NH₂OH and NH₃ at a platinum electrode in alkaline solution has been investigated using cyclic voltammetry. The results have been compared with the corresponding behaviour of these species at charged, porous cadmium and nickel hydroxide electrodes in order to understand the likely behaviour of NO₃ ^? impurities in nickelcadmium cells. The reactions are shown to be irreversible processes and strongly dependent on the nature of the electrode surfaces. The reactions which are likely to be involved in a charged cell can be represented by the overall scheme: $${\text{NO}}_{\text{3}} ^\_ {\text{NO}}_{\text{2}} ^\_ {\text{NH}}_{\text{3}} \xrightarrow{{{\text{slow}}}}{\text{N}}_2 $$ It is suggested that the self-discharge of cells containing NO₃ ^? is limited by slow kinetic effects rather than by diffusion as previously supposed.     

Simultaneous sulfide and acetate oxidation under denitrifying conditions using an inverse fluidized bed reactor

BACKGROUND: Simultaneous removal of sulfur, nitrogen and carbon compounds from wastewaters is a commercially important biological process. The objective was to evaluate the influence of the CH₃COO^?/NO₃^? molar ratio on the sulfide oxidation process using an inverse fluidized bed reactor (IFBR). RESULTS: Three molar ratios of CH₃COO^?/NO₃^? (0.85, 0.72 and 0.62) with a constant S^2?/NO₃^? molar ratio of 0.13 were evaluated. At a CH₃COO^?/NO₃^? molar ratio of 0.85, the nitrate, acetate and sulfide removal efficiencies were approximately 100%. The N₂ yield (g N₂ g^?1 NO₃^?‐N consumed) was 0.81. Acetate was mineralized, resulting in a yield of 0.65 g inorganic‐C g^?1 CH₃COO^?‐C consumed. Sulfide was partially oxidized to S⁰, and 71% of the S^2? consumed was recovered as elemental sulfur by a settler installed in the IFBR. At a CH₃COO^?/NO₃^? molar ratio of 0.72, the efficiencies of nitrate, acetate and sulfide consumption were of 100%, with N₂ and inorganic‐C yields of 0.84 and 0.69, respectively. The sulfide was recovered as sulfate instead of S⁰, with a yield of 0.92 g SO₄^2?‐S g^?1 S^2? consumed. CONCLUSIONS: The CH₃COO^?/NO₃^? molar ratio was shown to be an important parameter that can be used to control the fate of sulfide oxidation to either S⁰ or sulfate. In this study, the potential of denitrification for the simultaneous removal of organic matter, sulfide and nitrate from wastewaters was demonstrated, obtaining CO₂, S⁰ and N₂ as the major end products. Copyright © 2008 Society of Chemical Industry     

Radiolysis of Fremy's Salt in the Presence of Some Hydrated Electron Scavengers in Alkaline Aqueous Solution

Fremy's salt, ON(SO₃)₂^2?, was irradiated with γ-rays in deaerated alkaline aqueous solutions in the presence of NO₃^?, N₂O. In the presence of N₂O an increase of the G(-ON(SO₃)₂^2? = G from 6.1 to about 6.7 was observed within a limited range of concentration, while with NO₃^? the change is gradual. This is consistent with NO₂ and OH produced, respectively, in the reaction of e_aq^? with Fremy's salt, taking place in one-electron-equivalent processes, and with the assumption that pairs of radicals may originate from water molecules.     

Electrical Aspects of Adsorbing Colloid Flotation. X. Pretreatments,Multiple Removals,Interferences, and Specific Adsorption

Abstract

The compatibility of the adsorbing colloid flotation of Cu(II) with Fe(OH)₃ and sodium lauryl sulfate with a variety of precipitation pretreatment techniques was studied. Procedures were developed which permitted precipitation pretreatment and effective foam flotation polishing. The interferences of glycerol, ClO₄ ^?, NO₃ ^?, C1^?, CN^?, CNS^?, F^?, SO4₄ ^2?, HPO₄ ^2?, HAsO₄ ^2?, C₂O₄ ^2?, (PO₃)₆ ^6?, and EDTA with the precipitate flotation of ferric hydroxide by sodium lauryl sulfate were studied. The simultaneous adsorbing colloid flotation of Cu(II), Pb(II), and Zn(II) with Fe(OH)₃ and sodium lauryl sulfate was found to be effective in the pH range 6 to 7 at ionic strengths below 0.1 mole/l. A model was analyzed for calculating surface potentials for floe surfaces having the charge distributed at discrete sites in the presence of electrolytes. Plots of surface potential versus adsorbable ion concentration were calculated for various values of the model parameters.     

The mechanism of the nitrate (platinum) electrode in molten alkali nitrates

The mechanism for the nitrate electrode, (Pt)NO₂, O₂/NO^?₃, is shown to be: NO^?₂ = NO₂ + e; NO₂ = NO + $\text{1}\text{2}$O₂; NO^?₃ + NO = NO^?₂ + NO₂; with the overall reaction: NO^?₃ = NO₂ + $\text{1}\text{2}$O₂ + e.     

Kinetics,degradation pathway and reaction mechanism of advanced oxidation of 4‐nitrophenol in water by a UV/H2O2 process

Photooxidation of 4‐nitrophenol (4‐NP) in water by the UV/H₂O₂ advanced oxidation process was carried out in order to investigate the kinetics and pathway of 4‐NP degradation. The experimental results showed that the photodegradation of 4‐NP accorded well with pseudo‐first order kinetics. The effects of different parameters, such as H₂O₂ dosage, pH value and various anion scavengers on the degradation of 4‐NP have been investigated in detail. It was found that acidic conditions are more favorable to the degradation of 4‐NP but many anions, such as HCO₃^?, NO₃^? and Cl^?, slow down the photooxidation rate of 4‐NP. Hydroquinone, 1,2,4‐trihdroxybenzene, 4‐nitropyrogallol, and 4‐nitrocatechol were tentatively identified as the intermediates of 4‐NP degradation by GC/MS after samples were derivatized by N,O‐bis(trimethylsilyl)‐trifluoroacetamide (BSTFA). A degradation pathway was proposed to account for the observed intermediates produced during 4‐NP degradation by the UV/H₂O₂ process. Copyright © 2003 Society of Chemical Industry     

Membrane separation process modeling for CO2 partial removal in prepurification of air separation units

A novel membrane/adsorption hybrid system was proposed for air prepurification in large scale air separation units. Mathematical models were established for cocurrent and countercurrent flow patterns with crude nitrogen as purge stream to describe the membrane separation performance. The experimental and predicted results are in good agreement confirming the validity of the mathematical models. Effects of membrane properties and operation parameters on O₂ recovery, N₂ recovery, and membrane area requirement were investigated. For countercurrent flow pattern, O₂ recovery and N₂ recovery were larger than 98 and 99%, respectively, and membrane area requirement was less than 0.25?m²/m³?h^?1 with feed side pressure of 0.6?MPa and the purge gas/feed gas ratio of 0.2.     

Ion Flotation of Chromium(VI) Species: pH,Ionic Strength,Mixing Time,and Temperature

Abstract

Batch foam separation experiments of Cr(VI) anions with the cationic surfactant, ethylhexadecyldimethylammonium bromide, show a sharp increase in the flotation stoichiometry from 1.0 to 2.0⁺ over pH 6-8, corresponding to the conversion of Cr₂O₇ ^2?(HCrO₄ ^?) to CrO₄ ^2? with pH. In the acidic region for approximately 1.0×10^?3 M Cr(VI) solutions, the maximum increase in the flotation stoichiometry and decrease in the fractional removal of Cr₂O₇ ^2? is 12% over a fortyfold increase in ionic strength, varied with four different monoand divalent salts; the effect is produced by a small increase in the solubility of the (EHDA)₂Cr₂O₇ precipitate. In the basic region, a twentyfold increase in ionic strength with NaCl produces greater than 100% changes in the same flotation parameters, indicating a foam fractionation mechanism and competition between Br^?, Cl^? and CrO₄ ^2? for surfactant exchange sites. A temperature increase from 23 to 33°C in the acidic region has no effect on the flotation, and the lack of the effect of the mixing time between the Cr(VI) and surfactant solutions over the full range of variables permits all reported data points to be the average of four replicates, within ±3%.     

Foam Separation of Anions: Stoichiometry

Abstract

Experimental studies have been carried out on the foam separation of I^?, HCrO₄ ^?, S₂O₃ ^2?, and Ag(S₂O₃)₂ ^3? using a cationic surfactant as the collector-frother. The object of the work is the establishment of the Stoichiometry of the foam-separated surfactant cation-anion product to gain some insight into the mode of interaction between the surfactant and the anion. The Stoichiometry, S, defined as the ratio of the rate of surfactant removal to the rate of anion (colligend) removal at the gas bubble interfaces, ranges from 2.2–2.8 mole/mole (average values) for S₂O₃ ^2?, being a function of foaming time for the only system which does not involve the formation of particulates between the surfactant and the colligend. For HCrO₄ ^?, I^?, and Ag(S₂O₃)₂ ^3?, S is constant with foaming time and a participate product is formed in the bulk solution and/or the froth. For HCrO_4-, S is close to unity and is almost independent of the feed surfactant/colligend ratio, indicating minimum free surfactant. For I-, S averages 1.3 and is a weak function of the feed ratio, indicating that free surfactant is significant. Steric effects or secondary adsorption or exchange of Ag(S₂O₃)₂ ^3? the particulates makes S a linear function of the feed ratio.     

A chromotropic acid modified SBA-15 as a highly sensitive fluorescent probe for determination of Fe<Superscript>3+</Superscript> and I<Superscript>−</Superscript> ions in water

A novel organic–inorganic hybrid nanomaterial (SBA-15-CA) was prepared by covalent immobilization of chromotropic acid onto the surface of mesoporous silica material SBA-15. Different techniques such as XRD, TEM, FT-IR, N₂ adsorption–desorption and TGA analyses were employed to characterize the grafting process. The data showed that the organic moiety (0.41 mmol g^?1) was successfully grafted to the SBA-15 and the primary hexagonally ordered mesoporous structure of SBA-15 was preserved after the grafting procedure. SBA-15-CA has been realized as a highly sensitive and selective fluorescent probe towards Fe³⁺ and I^? ions in aqueous media. SBA-15-CA exhibited a remarkable fluorescent quenching in the presence of Fe³⁺ ion over other competitive cations including Na⁺, Mg²⁺, Al³⁺, K⁺, Ca²⁺, Cr³⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Hg²⁺, and Pb²⁺ as well as I^? ion among a series of anions including F^?, Cl^?, Br^?, CO₃^2?, HCO₃^?, CN^?, NO₃^?, NO₂^?, SCN^?, SO₄^2?, H₂PO₄^?, HPO₄^2?, and CH₃COO^?. A good linear response was observed between the concentration of the quenchers (Fe³⁺ and I^? ions) and fluorescence intensity of SBA-15-CA with detection limits of 1.5?×?10^?7 M for Fe³⁺ and 0.2?×?10^?7 M for I^?. Moreover, the effects of various pH values on the sensing ability of SBA-15-CA were investigated. Finally, the proposed method was successfully utilized for the determination of Fe³⁺ and I^? ions in river water, well water and tap water samples.     

Intermediate temperature electrochemical properties of lutetium-doped SrCeO3/SrZrO3-molten carbonate composite electrolyte

A SrCe_0.6Zr_0.3Lu_0.1O_3-α electrolyte was synthesized via a citric-nitrate auto-combustion (CNA) method using Sr(NO₃)₂, Zr(NO₃)₄·5H₂O, (NH₄)₂Ce(NO₃)₆, Lu₂O₃, HNO₃ and citric acid as raw materials. Subsequently, it reacted with the molten carbonate salt to obtain the SrCe_0.6Zr_0.3Lu_0.1O_3-α-Li₂CO₃-Na₂CO₃ composite electrolyte. The morphology, structure, conductivity and fuel cell performance of the obtained samples were investigated. SrCe_0.6Zr_0.3Lu_0.1O_3-α is fully dense after calcinated at 1540?°C for 5?h SrCe_0.6Zr_0.3Lu_0.1O_3-α and Li₂CO₃-Na₂CO₃ combined with each other to form a homogeneous interconnected structure. The highest power density and conductivity of SrCe_0.6Zr_0.3Lu_0.1O_3-α-Li₂CO₃-Na₂CO₃ are 255?mW?cm^?2 and 8.6?×?10^?2?S?cm^?1 at 600?°C, respectively.     

EFFECT OF ANIONS ON THERMODYNAMICS OF EXTRACTION OF Am(III) AND Eu(III) WITH OCTYL(PHENYL)-N,N-DIISOBUTYL-CARBAMOYLMETHYLPHOSPHINE OXIDE

The extraction of Am(III) and Eu(III) by octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) in xylene from aqueous media containing 1.0 M NH₄NO₃, NH₄SCN, NH₄ClO₄ or a mixture of 0.3 M NH₄NO₃ + 0.7 M NH₄ClO₄ at pH 2.70 and at the temperatures of 15, 25, 35 and 45±0.1 °C has been studied. At all the temperatures, the species extracted were ML₃ · 3CMPO (M = Am(III) or Eu(III), L = NO₃ ^?, SCN^? or ClO₄ ^?) and M(NO₃)(ClO₄)₂ · 3CMPO. The thermodynamic parameters of the extraction reactions have been evaluated using the temperature coefficient method. The ?ΔG values follow the order SCN^? > NO₃ ^? + ClO₄ ^? > NO₃ ^? ≈ ClO₄ ^?, whereas the ?ΔH values an order NO₃ ^? + ClO₄ ^? > SCN^? > NO₃ ^? ≈ ClO₄ ^?. The effect of these anions on the thermodynamic parameters have been discussed employing compensation effects and also on the basis of the energy associated with the transfer of these anions from aqueous to the extractant phase.     

Effects of anions on the photocatalytic and photoelectrocatalytic degradation of reactive dye in a packed‐bed reactor

The effects of various anions, Cl^?, ClO₄^?, SO₄^2?, NO₃^?, HCO₃^?, H₂PO₄^? and C₂O₄^2?, on the photocatalytic and photoelectrocatalytic degradation of reactive Brilliant Orange K‐R have been investigated in a packed‐bed photoelectrocatalytic reactor. It was found that the nature and concentrations of these inorganic anions significantly affected the photocatalytic and photoelectrocatalytic degradation performance of the reactive dye. The results indicated that the external electric field was successfully applied to improve the photocatalytic efficiency of reactive Brilliant Orange K‐R in the presence of Cl^?, especially at higher concentrations, while other inorganic anions displayed more or less negative effects on the degradation of the dye. The strongest inhibition effect on photocatalytic and photoelectrocatalytic degradation of the dye was observed in the presence of HCO₃^? ions. Copyright © 2004 Society of Chemical Industry     

Synthesis of Fe3O4/polyaniline nanocomposite and its application for nitrate removal from aqueous solutions

The aim of this work was to investigate the sorption characteristics of Fe₃O₄ coated on polyaniline (Fe₃O₄/PAn) for the removal of NO₃^? ions from aqueous solutions. The sorption of NO₃^? ions by the batch method was carried out. The optimum conditions of sorption were found to be a Fe₃O₄/PAn dose of 0.4 g in 100 mL of NO₃^? solution, a contact time of 10 min, pH and temperature 7 and 40°C, respectively. Temperature had a negative effect on the removal efficiency. Three equations, i.e., Morris–Weber, Lagergren, and pseudo‐second‐order, were tested to track the kinetics of the removal process. The Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models were subjected to sorption data in order to estimate sorption capacity, intensity, and energy. The thermodynamic parameters ΔH, ΔS, and ΔG were evaluated. They showed that the adsorption of NO₃^? onto Fe₃O₄/PAn was feasible, spontaneous, and exothermic under the studied conditions. It can be concluded that Fe₃O₄/PAn has potential to remove NO₃^? ions from aqueous solutions at different concentrations. The system Fe₃O₄/Pan was successfully tested for a high removal efficiency of NO₃^? from urban wastewater. J. VINYL ADDIT. TECHNOL., 19:147–156, 2013. © 2013 Society of Plastics Engineers     

Low-Temperature NOX (x = 1, 2) Removal with •OH Radicals from Catalytic Ozonation over α-FeOOH

FeOOH(H), FeOOH(P) and FeOOH(O) prepared by hydrothermal, precipitant-hydrolysis and oxidation-hydrolysis methods were tested as ozonation catalysts for the low-temperature NO_X (x = 1, 2) removal. FeOOH(H) exhibits higher catalytic activities than FeOOH(P) and FeOOH(O), achieving 85.6% of NO_X removal efficiency with a low ozone concentration. Compared to FeOOH(P) and FeOOH(O), FeOOH(H) shows much higher BET surface areas and higher density of surface -OH, both of which are critical for the ?OH radical generation over the catalysts. These radicals can be successfully transferred into the duct under the coupling effect of hydroxyl radicals and O₃, oxidizing and removing the NO_X (x = 1, 2). Results of ion chromatography (IC) indicate that the oxidation products are all NO₃^? without any NO₂^? in the tail solutions.     

The effect of sintering atmospheres on the properties of CSBT-0.15 ferroelectric ceramics

Ca_0.15Sr_1.85Bi₄Ti₅O₁₈ (CSBT-0.15) ferroelectric ceramics were developed by the conventional solid-state reaction method under various sintering atmospheres. The influences of these sintering atmospheres on grain orientation, grain size, oxygen vacancies, ferroelectric properties and leakage mechanisms were systematically investigated. It was found that the samples sintered under N₂ showed higher a-axis orientation and smaller grain sizes than those sintered under O₂ and air. From XPS analysis, it can be observed that the amount of Ti³⁺ in the ceramics sintered under N₂ is relatively high, which indicates a high number of oxygen vacancies in these samples. The samples sintered under N₂, air and O₂ all delivered well-saturated hysteresis loops with a remnant polarization (2Pr) of 13.8?μC/cm², 12.4?μC/cm² and 7.2?μC/cm² and corresponding coercive fields (2Ec) of 100?kV/cm, 86?kV/cm and 80?kV/cm, respectively. At 70?kV/cm, the leakage current densities of the samples sintered under N₂, air and O₂ are 4.2?×?10^?6 A/cm², 1.9?×?10^?6 A/cm² and 1.0?×?10^?6 A/cm², respectively. The leakage conduction mechanism transformed from Ohmic conduction in a relatively low applied electric field range (0–15?kV/cm) to space-charge-limited conduction (SCLC) in higher electric field ranges.     

Kinetic modeling and dynamic simulation for the catalytic wet air oxidation of aqueous ammonia to molecular nitrogen

A kinetic model for the catalytic wet air oxidation of aqueous ammonia over Ru/TiO₂ catalyst was developed considering the consecutive reaction steps as follows: (i) formation of active oxygen sites O* by the dissociative adsorption of aqueous O₂ on the catalyst, (ii) oxidation of aqueous NH₃ by the reaction with three O* sites to produce HNO₂, (iii) aqueous phase dissociation of HNO₂ into H⁺ and NO ₂ ^? , (iv) formation of NH ₄ ⁺ by the association of NH₃ with the HNO₂-dissociated H⁺, (v) formation of N₂ by the aqueous phase reaction between NO ₂ ^? and NH ₄ ⁺ , (vi) formation of NO₃ by the reaction of NO ₂ ^? with an O* site. For each reaction step, a rate equation was derived and its kinetic parameters were optimized by experimental data fitting. Activation energies for the reactions (ii), (v), and (vi) were 123.1, 76.7, and 54.5 kJ/mol, respectively, suggesting that the oxidation reaction of aqueous NH₃ to HNO₂ was a ratedetermining step. From the simulation using the kinetic parameters determined, the initial pH adjustment of the ammonia solution proved to be critical for determining the oxidation product selectivity between desirable N₂ and undesirable NO ₃ ^? as well as the degree of oxidation conversion of ammonia.     

Electrode reactions of nickel(II) at mercury electrodes in aqueous solutions of pyridine at high ionic strengths

At high ionic strength the ion pair (NiPy²⁺₄, nX^?) or complex (NiPy₄X₂), n = 0, 1, 2; X^? = Cl^?, Br^?, SCN^?, N^?₃, F^?, NO^?₃, ClO^?₄; is adsorbed at the surface of mercury electrode. Under specified conditions in chloride, bromide, and thiocyanates solutions the electroreduction is preceded by a crystallization of a complex on the electrode surface. The inductive role of specifically coadsorbed Cl^? ions is discussed.     

The absorption rate of CO2/SO2/NO2 into a blended aqueous AMP/ammonia solution

The Inter-governmental Panel on Climate Change (IPCC) reported that human activities result in the production of greenhouse gases (CO₂, CH₄, N₂O and CFCs), which significantly contribute to global warming, one of the most serious environmental problems. Under these circumstances, most nations have shown a willingness to suffer economic burdens by signing the Kyoto Protocol, which took effect from February 2005. Therefore, an innovative technology for the simultaneously removal carbon dioxide (CO₂) and nitrogen dioxide (NO₂), which are discharged in great quantities from fossil fuel-fired power plants and incineration facilities, must be developed to reduce these economical burdens. In this study, a blend of AMP and NH₃ was used to achieve high absorption rates for CO₂, as suggested in several publications. The absorption rates of CO₂, SO₂ and NO₂ into aqueous AMP and blended AMP+NH₃ solutions were measured using a stirred-cell reactor at 293, 303 and 313 K. The reaction rate constants were determined from the measured absorption rates. The effect of adding NH₃ to enhance the absorption characteristics of AMP was also studied. The performance of the reactions was evaluated under various operating conditions. From the results, the reactions with SO₂ and NO₂ into aqueous AMP and AMP+NH₃ solutions were classified as instantaneous reactions. The absorption rates increased with increasing reaction temperature and NH₃ concentration. The reaction rates of 1, 3 and 5 wt% NH₃ blended with 30 wt% AMP solution with respect to CO₂/SO₂/NO₂ at 313 K were 6.05～8.49×10^?6, 7.16–10.41×10^?6 and 8.02～12.0×10^?6 kmol m^?2s^?1, respectively. These values were approximately 32.3–38.7% higher than with aqueous AMP solution alone. The rate of the simultaneous absorption of CO₂/SO₂/NO₂ into aqueous AMP+NH₃ solution was 3.83–4.87×10^?6 kmol m^?2s^?1 at 15 kPa, which was an increase of 15.0–16.9% compared to 30 wt% AMP solution alone. This may have been caused by the NH₃ solution acting as an alternative for CO₂/SO₂/NO₂ controls from flue gas due to its high absorption capacity and fast absorption rate.