Mol Of Na Research Articles

Accessing Cation and Anion Redox in a 1-D Iron-Chalcogenide, Na3Fe2S4-XSex (x = 0, 2, & 4), in Na-Ion Batteries

The utilization of anionic redox activity is gaining significant interest in chalcogen based alkali-ion batteries. In this study, we are reporting reversible Na-ion (de)intercalation in one-dimensional structure of Na3Fe2S4-xSex (x = 0, 2, and 4). The crystal structure of Na3Fe0.5 2+Fe0.5 3+Q4 (Q = S and Se) can be visualized as a mixed valent iron, Fe2+/Fe3+ , forming infinite edge-shared chain of FeQ 4 tetrahedra with Na-ion residing in the interchain voids. While cycling the cathodes within a potential range of 1.5 – 2.5 V vs. Na/Na+, we could reversibly (de)intercalate one mole of Na from the structure. Mössbauer spectroscopy reveals a complete Fe2+ to Fe3+ oxidation in all the charged samples. Substitution of less electronegative Se2– in the structure systematically lowers the Fe2+/3+ redox couple during cycling. After 100 cycles at 1C rate, the cathode retains 83 % of its initial reversible capacity. While cycling the same cathode at a higher voltage range of 1.5 – 3.0 V, we observed a flat plateau profile at ~2.6 V with capacity reaching 255 mAh/g for Na3Fe2S4 cathode. This high capacity can be directly attributed to the anion oxidation for the charge compensation process during ~3.0 Na-ion deintercalation as supported by XPS analysis. The flat plateau profile further decreases from 2.6 to 2.5 V with the substitution of Se2–. The GITT results show two distinct kinetic behavior for the cation (fast) and anion (sluggish) redox. The decoupling of cation and anion redox in this system can enable us to understand and optimize the utilization of both redox chemistries to achieve a high energy density cathode.

Cathode reaction models for Braga-Goodenough Na-ferrocene and Li-MnO2 rechargeable batteries

Braga-Goodenough all-solid-state Na-Fc and Li-MnO2 batteries demonstrate deposition of Na and Li on the cathode during discharge. These reaction mechanisms were investigated in light of the generalized charge neutrality level and the experimental results of Braga et al., and two new types of mechanisms were proposed. The Na-Fc mechanism is represented by a multi-step C[(CE)cC]n mechanism where C is the chemical step, E is the electrochemical step, c is the catalytic (CE) step, and n denotes the number of [(CE)cC] part cycles. The nth cycle corresponds to n moles of Na and Li deposition. For Li-MnO2, two mechanisms were considered. One is the C[(CE)cC]n mechanism which is the same as Na-Fc, and the other is the C[2(CE)cC]n mechanism, which involves two consecutive (CE)c steps. In the C step of (CE)c of both mechanisms, Fc and MnO2 reduce Na+(sf) and Li+(sf) (sf - surface states) to deposit Na and Li, respectively, which are intramolecular charge transfer reactions within the adsorbed molecules. Fc and MnO2 are oxidized to inter­mediates immediately reduced to Fc and MnO2 by their anodes in the subsequent E step. Based on these mechanisms, these batteries' discharge capacity and cathode alkali metal deposition were examined in detail.

Understanding the Structural Phase Transitions in Na3V2(PO4)3 Symmetrical Sodium-Ion Batteries Using Synchrotron Based X-Ray Techniques

Sodium ion batteries (SIBs) are the promising candidate for large scale applications due to their high abundance and low cost.The symmetrical SIBs (similar cathode and anode configuration) are highly promising as they exhibit negligible volume changes during the charge/discharge process and making SIBs highly stable. Several NASICON (sodium superionic conductor) have high potential towards symmetrical SIBs due to presence of multi-redox reactions in both anodic and cathodic regions. Na3V2(PO4)3 (NVP) has been found to be appeal for symmetrical SIB systems due to presence of flat voltage profile, multi-redox with a single transition metal, and a large working voltage difference between anodic and cathodic regions can greatly improve the output of the NVP symmetrical cell. However, the phase transitions associated during the electrochemical reaction in the symmetrical NVP cells are not widely studied. The synchrotron X-ray studies in NVP symmetrical cells confirms the redox reaction involving ≈2 moles of Na+ reaction instead of 1 mole of Na+ reaction. The in-situ X-ray diffraction and X-ray absorption spectroscopy during the electrochemical cycling confirms the reversible formation of Na5V2(PO4)3 phase in the anode and NaV2(PO4)3 phase in the cathode. The charge storage process in NVP cathode region is through V3+/V4+ redox, and charge storage process in NVP anode region is through V3+/V2+ redox. The 2 moles sodium-ion storage process can make a discharge capacity of ≈99 mAh g−1, increasing the energy output of the symmetrical NVP.

Thermodynamic and kinetic properties of Li3BO3 modified by the alkali fluorides addition in the CO2 capture process

Tri-lithium borate (Li3BO3) is a high-capacity CO2 sorbent recently proposed for the intermediate temperature range of 500 °C to 650 °C. Up to date, only a study of CO2 sorption kinetic behavior of Li3BO3 modified by nitrite salts has been carried out. The equilibrium properties that relate the dependence of the partial pressure of CO2 and temperature are also unknown. In this work, a novel two-step mechano-thermal method was optimized to produce both pure and modified Li3BO3 by addition of 0.1 mol of Na- and K-fluorides. Fast reaction by milling of Li2CO3 and H3BO3 forms the intermediate LiB5O8·5H2O compound at room temperature, which transforms to Li3BO3 as single phase by heating at 600 °C. Pressure-composition isotherms allow to determine the existence of two plateaus, each of them ascribed to different phases: Li6B4O9 at low CO2 partial pressure (ΔH = 58 ± 5 kJ/mol) and LiBO2 at high CO2 partial pressure (ΔH = 106 ± 6 kJ/mol). The mathematical expression that relates the equilibrium CO2 absorption partial pressure and the temperature of modified and unmodified Li3BO3 was reported. Na- and K-modified Li3BO3 show remarkably fast kinetics with high CO2 capture capacity (e.g. greater than 45 wt% at 500 °C) and excellent regenerability, with minor deterioration in performance over 30 cycles of CO2 sorption. The kinetic behavior of modified Li3BO3 by alkali fluorides is enhanced by the formation of an eutectic melt phase during carbonation, as confirmed by differential scanning calorimetry and the simultaneous detection of LiF. In addition, alkali fluorides could generate oxygen vacancies and modify the surface composition by enrichment of Li-O sites, also favoring the CO2 sorption kinetics.

Understanding the Structural Phase Transitions in Na3 V2 (PO4 )3 Symmetrical Sodium-Ion Batteries Using Synchrotron-Based X-Ray Techniques.

Sodium-ion batteries (SIBs) hold great potential for use in large-scale grid storage applications owing to their low energy cost compared to lithium analogs. The symmetrical SIBs employing Na3 V2 (PO4 )3 (NVP) as both the cathode and anode are considered very promising due to negligible volume changes and longer cycle life. However, the structural changes associated with the electrochemical reactions of symmetrical SIBs employing NVP have not been widely studied. Previous studies on symmetrical SIBs employing NVP are believed to undergo one mole of Na+ storage during the electrochemical reaction. However, in this study, it is shown that there are significant differences during the electrochemical reaction of the symmetrical NVP system. The symmetrical sodium-ion cell undergoes ≈2 moles of Na+ reaction (intercalation and deintercalation) instead of 1 mole of Na+ . A simultaneous formation of Na5 V2 (PO4 )3 phase in the anode and NaV2 (PO4 )3 phase in the cathode is revealed by synchrotron-based X-ray diffraction and X-ray absorption spectroscopy. A symmetrical NVP cell can deliver a stable capacity of ≈99mAhg-1 , (based on the mass of the cathode) by simultaneously utilizing V3+ /V2+ redox in anode and V3+ /V4+ redox in cathode. The current study provides new insights for the development of high-energy symmetrical NIBs for future use.

Electrostatic Self-Assembly Synthesis of Three-Dimensional Mesoporous Lepidocrocite-Type Layered Sodium Titanate as a Superior Adsorbent for Selective Removal of Cationic Dyes via an Ion-Exchange Mechanism.

Three-dimensional mesoporous lepidocrocite-type layered sodium titanate (LST) was constructed at room temperature by the electrostatic interaction between Ti1-δO24δ- nanosheets and Na+ ions. The results of a systematic X-ray diffraction investigation manifested the transition from the Ti1-δO24δ- nanosheets phase to the titanate/titania phase, which determined a phase diagram as a function of the temperature and NaCl concentration. In addition, scanning electron microscopy, inductively coupled plasma-mass spectrometry, thermogravimetric and differential thermal, N2 adsorption-desorption, Raman spectroscopy, Fourier transform infrared spectroscopy, as well as ζ-potential analyses were utilized for adequate characterization of the LST physical and chemical properties. Furthermore, batch adsorption experiments demonstrated that LST had superior adsorption property and adsorption selectivity toward cationic dyes compared to those of anionic dyes. A multifarious influencing effect on the cationic dye adsorption behavior during the adsorption process was systematically investigated. Moreover, the pseudo-second-order kinetic model felicitously depicted the cationic dye adsorption behavior through an elaborate kinetic study, namely, chemisorption was the main adsorption action. Meanwhile, different adsorption isotherm models were utilized to process the experimental data, uncovering that the adsorption isotherms of cationic dyes on LST were suitable for a Langmuir isothermal model. More importantly, an ion-exchange mechanism was proposed for the cationic dye adsorption on LST, and the ion-exchange reaction occurred with a stoichiometric exchange between 1 mol of Na+ ions in the LST interlayer and 1 mol of MB molecules in the solution. In parallel, the electrochemical impedance spectroscopy and cyclic voltammogram measurements verified that the high ionic conductivity of Na+ ions in the LST interlayer resulted in a superior adsorption property. A two-step acid-base procedure was ultimately adopted to effectively regenerate LST adsorbent. This work provides not only an alternative adsorbent with superior adsorption capacity and adsorption selectivity but also some guiding significance for research on the adsorption mechanism of layered titanates.

Multi-Redox (V5+/V4+/V3+/V2+) Driven Asymmetric Sodium (De)intercalation Reactions in NASICON-Na3VIn(PO4)3 Cathode

NASICON-Na3V2−xMx(PO4)3 (M = Al3+, Cr3+, Fe3+ & Ga3+) cathodes are attractive for sodium-ion battery application due to their high voltage multi-redox (V5+/V4+/V3+) couples and faster sodium-ion diffusivity. However, they suffer from rapid capacity decay due to irreversible structural changes occurring at high voltages. Herein, we present the structural and electrochemical sodium (de)intercalation properties of NASICON-Na3VIn(PO4)3 (NVIP) cathode. Although, this In3+-substituted cathode also undergoes similar high voltage structural degradation, but its structure is rejuvenated through the following low voltage deep-sodiation process, resulting in reversible capacities of ∼145 mA h g−1 (i.e., equivalent to ∼2.82 moles of Na per vanadium). Our combined electrochemical, in-operando X-ray diffraction and exsitu X-ray absorption spectroscopy analyses reveal asymmetric sodium (de)intercalation pathways of the NVIP cathode in the window of 4.2–1.2 V vs Na+/Na0 that is driven by multi-redox (V5+/V4+/V3+/V2+) couples.

Fabricating 3D ordered marcoporous Na2MnSiO4/C with hierarchical pores for fast sodium storage

Despite being considered as a promising candidate for cathode of next-generation batteries, sodium manganese orthosilicate suffers from sluggish kinetics, while no effective enhancement through structural manipulation has been reported yet. Herein a three-dimensionally ordered macroporous Na2MnSiO4/C is fabricated via a templated sol-gel method and investigated as a cathode material for sodium ion batteries. It delivers a high initial reversible capacity of 207 mAh g−1 (∼1.5 mol of Na+ insertion/extraction) at 0.1 C (1C = 139 mAh g−1), excellent high-rate capability (76 mAh g−1 at 5 C) and long-term cyclability (76.0% after 345 cycles at 2 C). The superior electrochemical properties are ascribed to short Na-ion diffusion path of honeycomb-like 3D ordered macroporous structure, fast electron transportation of interconnected carbon frameworks and effective constraint of volumetric changes upon electrochemical cycling. The rational design of 3D ordered porous structure may facilitate the development of silicate-based cathode materials that have problems of low electronic conductivity, slow ion diffusion and structural instability for new high-energy sodium ion batteries.

P2-type Na0.53MnO2 nanorods with superior rate capabilities as advanced cathode material for sodium ion batteries

Layered P2-type Na0.53MnO2 nanorods is prepared by a simple solution reaction. When used as cathode material for sodium ion batteries, the P2-Na0.53MnO2 delivers a high reversible capacity up to 135.7mAhg−1 (theoretical capacity is 140mAhg−1) at 0.1C in the voltage range of 2–4.3V vs. Na+/Na, corresponding to 0.51mol of Na insertion/extraction. It presents good cycling performance and high rate capabilities. After 50 cycles, the capacity is just fading about 6.8% at the rate of 2C. The significant behaviour of fast charging makes it be very attractive for practical application. The electrochemical impedance spectroscopy and galvanostatic intermittent titration technique are employed to investigate its sodium diffusion kinetics. The ex-situ X-ray diffraction technology is also used to study the intercalation/de-intercalation of sodium ions and the phase transition in the charging/discharging processes.

Effect of Carbon Content on Morphology, Size and Phase of Submicron Tungsten Carbide Powders by Salt-assisted Combustion Synthesis

Abstract The diluent NaCl was introduced into the WO 3 -Mg-C-Na 2 CO 3 system to prepare submicron tungsten carbide (WC) powders via salt-assisted combustion synthesis. The products were analyzed by SEM, EDS and XRD, and the effects of C content on morphology, average particle size and phase composition of the products were studied. Results show that on basis of the m = 0.125 (the number of moles of Na 2 CO 3 ), when the number of moles of carbon in raw material increases from l =2 to 2.25 and 2.5, before leaching, the product is made up of a small number of large size particles and a large number of small size particles; after leaching, samples are composed of aggregates of submicron particles, and the sintering phenomenon between particles is very weak, indicating low degree of aggregation. Particle size distribution of leached product almost falls into the normal distribution, and the particle sizes range from 200 nm to 350 nm. Under the condition of l =2.25, a main target product is WC, and the content of by-products W 2 C is extremely few. That is, k = 2.0 (the number of moles of NaCl), m = 0.125, and l =2.25 are the process conditions for single-phase WC synthesis.

Synthesis and Electrochemical Performance of the Na3V2(PO4)3 Cathode for Sodium-Ion Batteries

Rhombohedral Na3V2(PO4)3 with a Na+ superionic conductor structure was synthesized using a solid-state reaction method. Citric acid was used as a carbon resource for carbon-thermal reduction reaction to reduce the oxidation state of vanadium. The shape of Na3V2(PO4)3 particles is irregular and its average diameter is in the range 30–50 nm. The Na3V2(PO4)3 exhibits a superior cycling ability and rate capability. The discharge capacity retains 74.3% of the discharge capacity of its first cycle with coulombic efficiency of 99.3% after 100 cycles. The discharge capacity of Na3V2(PO4)3 at 10 C is 48.87 mAh g−1, which is 58.4% of the cell cycled at 0.1 C. Furthermore, the structure of Na3V2(PO4)3 is stable for a considerable amount of Na+ ions (2 mol of Na+ ions) insertion and extraction with only 0.42% difference of unit-cell volume between fully charged and discharged states. Na3V2(PO4)3 is a potential cathode material for sodium-ion battery applications.

Layer-by-Layer Modification of Cation Exchange Membranes Controls Ion Selectivity and Water Splitting

The present study investigates the possibility of inducing monovalent ion permselectivity on standard cation exchange membranes, by the layer-by-layer (LbL) assembly of poly(ethyleneimine) (PEI)/poly(styrenesulfonate) (PSS) polyelectrolyte multilayers. Coating of the (PEI/PSS)N LbL multilayers on the CMX membrane caused only moderate variation of the ohmic resistance of the membrane systems. Nonetheless, the polyelectrolyte multilayers had a substantial influence on the monovalent ion permselectivity of the membranes. Permselectivity comparable to that of a commercial monovalent-ion-permselective membrane was obtained with only six bilayers of polyelectrolytes, yet with significantly lower energy consumption per mole of Na(+) ions transported through the membranes. The monovalent ion permselectivity stems from an increased Donnan exclusion for divalent ions and hydrophobization of the surface of the membranes concomitant to their modification. Double-layer capacitance obtained from impedance measurements shows a qualitative indication of the divalent ion repulsion of the membranes. At overlimiting current densities, water dissociation occurred at membranes with PEI-terminated layers and increased with the number of layers, while it was nearly absent for the PSS-terminated layers. Hence, LbL layers allow switching on and turning off water splitting at the surface of ion exchange membranes.

Carbon‐Coated LiTi2(PO4)3: An Ideal Insertion Host for Lithium‐Ion and Sodium‐Ion Batteries

We report the extraordinary performance of carbon-coated sodium super ion conductor (NASICON)-type LiTi2 (PO4 )3 as an ideal host matrix for reversible insertion of both Li and Na ions. The NASICON-type compound was prepared by means of a Pechini-type polymerizable complex method and was subsequently carbon coated. Several characterization techniques such as XRD, thermogravimetric analysis (TGA), field-emission (FE) SEM, TEM, and Raman analysis were used to study the physicochemical properties. Both guest species underwent a two-phase insertion mechanism during the charge/discharge process that was clearly evidenced from galvanostatic and cyclic voltammetric studies. Unlike that of Li (≈1.5 moles of Li), Na insertion exhibits better reversibility (≈1.59 moles of Na) while experiencing a slightly higher capacity fade (≈8 % higher than Li) and polarization (780 mV) than Li. However, excellent rate capability profiles were noted for Na insertion relative to its counterpart Li. Overall, the Na insertion properties were found to be superior relative to Li insertion, which makes carbon-coated NASICON-type LiTi2 (PO4 )3 hosts attractive for the development of next-generation batteries.

Thermodynamic Profiles and Nuclear Magnetic Resonance Studies of Oligonucleotide Duplexes Containing Single Diastereomeric Spiroiminodihydantoin Lesions

The spiroiminodihydantoins (Sp) are highly mutagenic oxidation products of guanine and 8-oxo-7,8-dihydroguanine in DNA. The Sp lesions have recently been detected in the liver and colon of mice infected with Helicobacter hepaticus that induces inflammation and the development of liver and colon cancers in murine model systems [Mangerich, A., et al. (2012) Proc. Natl. Acad. Sci. U.S.A. 109, E1820-E1829]. The impact of Sp lesions on the thermodynamic characteristics and the effects of the diastereomeric Sp-R and Sp-S lesions on the conformational features of double-stranded 11-mer oligonucleotide duplexes have been studied by a combination of microcalorimetric methods, analysis of DNA melting curves, and two-dimensional nuclear magnetic resonance methods. The nonplanar, propeller-like shapes of the Sp residues strongly diminish the extent of local base stacking interactions that destabilize the DNA duplexes characterized by unfavorable enthalpy contributions. Relative to that of an unmodified duplex, the thermally induced unfolding of the duplexes with centrally positioned Sp-R and Sp-S lesions into single strands is accompanied by a smaller release of cationic counterions (Δn(Na⁺) = 0.6 mol of Na⁺/mol of duplex) and water molecules (Δn(w) = 17 mol of H₂O/mol of duplex). The unfolding parameters are similar for the Sp-R and Sp-S lesions, although their orientations in the duplexes are different. The structural disturbances radiate one base pair beyond the flanking C:G pair, although Watson-Crick hydrogen bonding is maintained at all flanking base pairs. The observed relatively strong destabilization of B-form DNA by the physically small Sp lesions is expected to have a significant impact on the processing of these lesions in biological environments.

Localization of Ubiquinone-8 in the Na+-pumping NADH:Quinone Oxidoreductase from Vibrio cholerae

Na(+) is the second major coupling ion at membranes after protons, and many pathogenic bacteria use the sodium-motive force to their advantage. A prominent example is Vibrio cholerae, which relies on the Na(+)-pumping NADH:quinone oxidoreductase (Na(+)-NQR) as the first complex in its respiratory chain. The Na(+)-NQR is a multisubunit, membrane-embedded NADH dehydrogenase that oxidizes NADH and reduces quinone to quinol. Existing models describing redox-driven Na(+) translocation by the Na(+)-NQR are based on the assumption that the pump contains four flavins and one FeS cluster. Here we show that the large, peripheral NqrA subunit of the Na(+)-NQR binds one molecule of ubiquinone-8. Investigations of the dynamic interaction of NqrA with quinones by surface plasmon resonance and saturation transfer difference NMR reveal a high affinity, which is determined by the methoxy groups at the C-2 and C-3 positions of the quinone headgroup. Using photoactivatable quinone derivatives, it is demonstrated that ubiquinone-8 bound to NqrA occupies a functional site. A novel scheme of electron transfer in Na(+)-NQR is proposed that is initiated by NADH oxidation on subunit NqrF and leads to quinol formation on subunit NqrA.

The kinetics of cation exchange of amorphized terskite

The kinetics of cation exchange between natural amorphized microporous zirconosilicate terskite Na4ZrSi6O15(OH)2 · H2O and aqueous solutions of cesium fluoride was studied calorimetrically under isothermal conditions, in the temperature range of 27.5 to 55.2°C, at CsF concentrations of 0.6–2.2 mol/l. The rate of the process was described by the first-order kinetic equation with the rate constant k, h−1 = 3.1 × 103CCsF0.92 exp(−(21 ± 8) × 103/RT). Upon replacing Na+ with Cs+, the first-order equilibrium was observed to shift abruptly toward the Cs-substituted sorbent form, where Cs2O content after saturation was 25.5–29.1 wt %. The average heat of ion exchange Q0 over the temperature range 27.5–32.4°C was shown to be ∼3.4 kJ per 1 mol of Na+ ions. We conclude that sorbents based on A-terskite are of practical interest for the processes of extracting 137Cs isotope from water.

Influences of chemical activators on incinerator bottom ash

This research has applied different chemical activators to mechanically and thermally treated fine fraction (<14 mm) of incinerator bottom ash (IBA), in order to investigate the influences of chemical activators on this new pozzolanic material. IBA has been milled and thermally treated at 800 degrees C (TIBA). The TIBA produced was blended with Ca(OH)(2) and evaluated for setting time, reactivity and compressive strength after the addition of 0.0565 mole of Na(2)SO(4), K(2)SO(4), Na(2)CO(3), K(2)CO(3), NaOH, KOH and CaCl(2) into 100g of binder (TIBA+Ca(OH)(2)). The microstructures of activated IBA and hydrated samples have been characterized by X-ray diffraction (XRD) and thermogravimetry (TG) analysis. Thermal treatment is found to produce gehlenite (Ca(2)Al(2)SiO(7)), wollastonite (CaSiO(3)) and mayenite (Ca(12)Al(14)O(33)) phases. The thermally treated IBA samples are significantly more reactive than the milled IBA. The addition of Na(2)CO(3) can increase the compressive strength and calcium hydroxide consumption at 28-day curing ages. However, the addition of Na(2)SO(4), K(2)SO(4), K(2)CO(3), NaOH and KOH reduces the strength and hydration reaction. Moreover, these chemicals produce more porous samples due to increased generation of hydrogen gas. The addition of CaCl(2) has a negative effect on the hydration of TIBA samples. Calcium aluminium oxide carbonate sulphide hydrate (Ca(4)Al(2)O(6)(CO(3))(0.67)(SO(3))(0.33)(H(2)O)(11)) is the main hydration product in the samples with activated IBA, except for the sample containing CaCl(2).

Plotting of isolines of equal degree of precipitation in the FeCl2-Na2SO3-H2O system as the basis for isolation of ferrous sulfite from solution

Ferrous ions are removed from acidic solutions of nonferrous metal compounds by precipitation of Fe(OH) 3 after oxidation of Fe 2+ in solutions while increasing their pH. The mother solution of this product continues to contain valuable components, in particular, nonferrous metal ions irremovable by repeated repulping of the solution by acidified water. The utilization of ferric hydroxide is an important problem for various industries, first of all, nonferrous metallurgy [1]. We solved the problem of utilizing ferric hydroxide, which is now a production waste, by developing a technology based on sulfite conversion, the theoretical basis for which was a study of the pseudoquaternary system Fe(OH) 3 (H 2 SO 4 )‐Na 2 SO 3 ‐H 2 O [2]. For the first time, information was visualized by plotting on a plane of the multicomponent system a combination of two surfaces using two types of isolines: isolines of equal Fe(III) reduction state FeO 1.5 (final)/FeO 1.5 (initial) (%) and isolines of equal molar ratio Na 2 SO 3 /FeO 1.5 . This related the redox process with the reactant ratio and, thereby, clarified the mechanism of interaction in the system that is necessary for optimization and practical application of the process [3]. In the system Fe(OH) 3 (H 2 SO 4 )‐Na 2 SO 3 ‐H 2 O, three moles of Na 2 SO 3 react with one mole of Fe(OH) 3 to lead to virtually complete precipitation of ferrous sulfite. In this reaction, the reduction of Fe(III) to Fe(II) consumes two moles of Na 2 SO 3 , which is oxidized to dithionate Na 2 S 2 O 6 , and only one mole of Na 2 SO 3 is used to precipitate Fe(II) as sulfite FeSO 3 · 2.5H 2 O. In the technological process of sulfite conversion of ferrous cake, cake is initially separated by oxidizing the solution while increasing pH and then sulfitized to convert Fe(III) to Fe(II); ferrous sulfite precipitates; and sodium sulfite is recovered by thermal hydrolysis of the suspension, with SO 2 being distilled off and trapped by a Na 2 CO 3 solution. It seemed reasonable to develop a process of direct removal of ferrous sulfite from solution without a complex step of ferric hydroxide separation. For this purpose, it is necessary to investigate the FeCl 2 ‐Na 2 SO 3 ‐ H 2 O system at room temperature. This system has not yet been studied. The FeCl 2 ‐Na 2 SO 3 ‐H 2 O system was produced from a 0.18 M FeCl 2 solution (pH 2.6) and a 0.18 M Na 2 SO 3 solution (pH 8.4). The FeCl 2 solution was added to the H 2 SO 3 solution, and the mixture was supplemented with a 1 M H 2 SO 4 solution or a 1 M NaOH solution until a certain pH value from 4.0 to 1.5 at an interval of 0.5 was reached. H 2 SO 4 or NaOH was not a component of the pseudoternary system FeCl 2 ‐Na 2 SO 3 ‐(H + or OH ‐ )‐ H 2 O since either of the two substances was introduced only for reaching a certain pH value and was not involved in phase formation.

Reach-Scale Cation Exchange Controls on Major Ion Chemistry of an Antarctic Glacial Meltwater Stream

McMurdo dry valleys of Antarctica represent the largest of the ice-free areas on the Antarctic continent, containing glaciers, meltwater streams, and closed basin lakes. Previous geochemical studies of dry valley streams and lakes have addressed chemical weathering reactions of hyporheic substrate and geochemical evolution of dry valley surface waters. We examine cation transport and exchange reactions during a stream tracer experiment in a dry valley glacial meltwater stream. The injection solution was composed of dissolved Li+, Na+, K+, and Cl-. Chloride behaved conservatively in this stream, but Li+, Na+, and K+ were reactive to varying degrees. Mass balance analysis indicates that relative to Cl-, Li+ and K+ were taken up in downstream transport and Na+ was released. Simulations of conservative and reactive (first-order uptake or generation) solute transport were made with the OTIS (one-dimensional solute transport with inflow and storage) model. Among the four experimental reaches of Green Creek, solute transport simulations reveal that Li+ was removed from stream water in all four reaches, K+ was released in two reaches, taken up in one reach, and Na+ was released in all four reaches. Hyporheic sediments appear to be variable with uptake of Li+ in two reaches, uptake of K+ in one reach, release of K+ in two reaches, and uptake of Na+ in one reach. Mass balances of the conservative and reactive simulations show that from 1.05 to 2.19 moles of Li+ was adsorbed per reach, but less than 0.3 moles of K+ and less than 0.9 moles of Na+ were released per reach. This suggests that either (1) exchange of another ion which was not analyzed in this experiment or (2) that both ion exchange and sorption control inorganic solute transport. The elevated cation concentrations introduced during the experiment are typical of initial flows in each flow season, which flush accumulated dry salts from the streambed. We propose that the bed sediments (which compose the hyporheic zone) modulate the flushing of these salts during initial flows each season, due to ion exchange and sorption reactions.

Incorporation of a cationic aminopropyl chain in DNA hairpins: thermodynamics and hydration.

We report on the physicochemical effects resulting from incorporating a 5-(3-aminopropyl) side chain onto a 2'-deoxyuridine (dU) residue in a short DNA hairpin. A combination of spectroscopy, calorimetry, density and ultrasound techniques were used to investigate both the helix-coil transition of a set of hairpins with the following sequence: d(GCGACTTTTTGNCGC) [N = dU, deoxythymidine (dT) or 5-(3-aminopropyl)-2'-deoxyuridine (dU*)], and the interaction of each hairpin with Mg(2+). All three molecules undergo two-state transitions with melting temperatures (T(M)) independent of strand concentration that indicates their intramolecular hairpin formation. The unfolding of each hairpin takes place with similar T(M) values of 64-66 degrees C and similar thermodynamic profiles. The unfavorable unfolding free energies of 6.4-6.9 kcal/mol result from the typical compensation of unfavorable enthalpies, 36-39 kcal/mol, and favorable entropies of approximately 110 cal/mol. Furthermore, the stability of each hairpin increases as the salt concentration increases, the T(M)-dependence on salt yielded slopes of 2.3-2.9 degrees C, which correspond to counterion releases of 0.53 (dU and dT) and 0.44 (dU*) moles of Na(+) per mole of hairpin. Absolute volumetric and compressibility measurements reveal that all three hairpins have similar hydration levels. The electrostatic interaction of Mg(2+) with each hairpin yielded binding affinities in the order: dU > dT > dU*, and a similar release of 2-4 electrostricted water molecules. The main result is that the incorporation of the cationic 3-aminopropyl side chain in the major groove of the hairpin stem neutralizes some local negative charges yielding a hairpin molecule with lower charge density.