Search results for "Pitzer."
showing 10 items of 28 documents
Modeling S-carboxymethyl-L-cysteine protonation and activity coefficients in sodium and tetramethylammonium chloride aqueous solutions by SIT and Pit…
2007
Solubility and acid–base properties of S-carboxymethyl-l-cysteine (carbocysteine, ccys) in NaClaq and tetramethylammonium chloride, (CH3)4NClaq ,a tt =2 5 ◦ C and at different ionic strengths were investigated. Solubility was studied at 1.0 ≤ I (mol L −1 ) ≤ 5.0 for NaClaq and 1.0 ≤ I (mol L −1 ) ≤ 3.0 for (CH3)4NClaq, while potentiometric measurements (by ISE-H + , glass electrode) were performed at 0.1 ≤ I (mol L −1 ) ≤ 5.0 for NaClaq and 0.5 ≤ I (mol L −1 ) ≤ 3.0 for (CH3)4NClaq. Solubility data allowed us to determine Setschenow constants and activity coefficients of neutral carbocysteine (H2ccys). Dependence on ionic strength and ionic medium of protonation constants and activity coeff…
Hydrolysis and chemical speciation of dioxouranium(VI) ion in aqueous media simulating the major ion composition of seawater
2004
Abstract The hydrolysis and chemical speciation of the dioxouranium(VI) ion at 25 °C was studied in a number of binary electrolytes (LiCl, NaCl, MgCl2, CaCl2, Na2SO4) and some mixtures (NaCl–Na2SO4, NaNO3–Na2SO4, CaCl2–MgCl2) as well as artificial seawater (SSWE) as a function of ionic strength. The results in LiCl, CaCl2 and MgCl2 solutions confirmed the formation of (UO2)2(OH)22+, (UO2)3(OH)42+, (UO2)3(OH)5+ and (UO2)3(OH)7− species (at I=0 mol l−1: log Tβ22=−5.76, log Tβ34=−11.82, log Tβ35=−15.89 and log Tβ37=−29.26). For NaNO3, NaCl and artificial seawater the hydrolysis constant for the formation of the UO2(OH)+ species was also determined (at I=0 mol l−1: log Tβ11=−5.19). The results …
Novel solutions for closed-loop Reverse Electrodialysis: thermodynamic characterisation and perspective analysis
2019
Abstract Closed-loop Reverse Electrodialysis is a novel technology to directly convert low-grade heat into electricity. It consists of a reverse electrodialysis (RED) unit where electricity is produced exploiting the salinity gradient between two salt-water solutions, coupled with a regeneration unit where waste-heat is used to treat the solutions exiting from the RED unit and restore their initial composition. One of the most important advantages of closed-loop systems compared to the open systems is the possibility to select ad-hoc salt solutions to achieve high efficiencies. Therefore, the properties of the salt solutions are essential to assess the performance of the energy generation a…
Modeling ATP protonation and activity coefficients in NaClaq and KClaq by SIT and Pitzer equations.
2006
Abstract The acid–base properties of Adenosine 5′-triphosphate (ATP) in NaCl and KCl aqueous solutions at different ionic strengths (0 I / mol L − 1 ≤ 5 for NaCl aq , 0 I / mol L − 1 ≤ 3 for KCl aq ) and at t = 25 °C were investigated. A selection of literature data on ATP protonation constants and on activity isopiestic coefficients was performed, together with new potentiometric measurements (by ISE-H + , glass electrode). Both literature and new experimental data were used to model the dependence on ionic strength and ionic medium of ATP protonation by SIT (Specific ion Interaction Theory) and Pitzer equations. In addition to values of first and second ATP protonation constants in…
A stellar flare-coronal mass ejection event revealed by X-ray plasma motions
2019
Coronal mass ejections (CMEs), often associated with flares, are the most powerful magnetic phenomena occurring on the Sun. Stars show magnetic activity levels up to 10^4 times higher, and CME effects on stellar physics and circumstellar environments are predicted to be significant. However, stellar CMEs remain observationally unexplored. Using time-resolved high-resolution X-ray spectroscopy of a stellar flare on the active star HR 9024 observed with Chandra/HETGS, we distinctly detected Doppler shifts in S XVI, Si XIV, and Mg XII lines that indicate upward and downward motions of hot plasmas (~10-25 MK) within the flaring loop, with velocity v~100-400 km/s, in agreement with a model of fl…
The interaction of amino acids with the major constituents of natural waters at different ionic strengths
2000
Abstract The interaction of amino acids with the major constituents of natural waters has been studied potentiometrically by determining protonation constants at different ionic strengths (e.g., I ≤5.6 mol (kg H 2 O) −1 (NaCl)) and in artificial seawater (containing Na + , K + , Ca 2+ , Mg 2+ , Cl − and SO 4 2− ) at different salinities. For glycine determinations in mixed NaCl–MgCl 2 , electrolyte solutions were also performed. The data included in this work, together with some already published, make it possible to calculate parameters for dependence on ionic strength using different models, i.e. an extended Debye–Huckel type equation and Pitzer equations. The results can be interpreted b…
Protonation of Carbonate in Aqueous Tetraalkylammonium Salts at 25°C.
2006
Protonation constants of carbonate were determined in tetramethylammonium chloride (Me4NClaq 0.1≤I/mol kg−1 ≤4) and tetraethylammonium iodide (Et4NIaq 0.1≤I/mol kg−1 ≤1) by potentiometric ([H+]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaClaq (0.1≤I/mol kg−1 ≤6) were also critically analysed. Both protonation constants of carbonate follow the trend Et4NI>Me4NCl > NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electr…
SAX J1808.4-3658, an accreting millisecond pulsar shining in gamma rays?
2016
We report the detection of a possible gamma-ray counterpart of the accreting millisecond pulsar SAX J1808.4-3658. The analysis of ~6 years of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi-LAT) within a region of 15deg radius around the position of the pulsar reveals a point gamma-ray source detected at a significance of ~6 sigma (Test Statistic TS = 32), with position compatible with that of SAX J1808.4-3658 within 95% Confidence Level. The energy flux in the energy range between 0.6 GeV and 10 GeV amounts to (2.1 +- 0.5) x 10-12 erg cm-2 s-1 and the spectrum is well-represented by a power-law function with photon index 2.1 +- 0.1. We searched for si…
Multiple accelerated particle populations in the Cygnus Loop with Fermi-LAT
2021
The Cygnus Loop (G74.0-8.5) is a very well-known nearby supernova remnant (SNR) in our Galaxy. Thanks to its large size, brightness, and angular offset from the Galactic plane, it has been studied in detail from radio to $\gamma$-ray emission. The $\gamma$ -rays probe the populations of energetic particles and their acceleration mechanisms at low shock speeds. We present an analysis of the $\gamma$-ray emission detected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope over 11 years in the region of the Cygnus Loop. We performed detailed morphological and spectral studies of the $\gamma$-ray emission toward the remnant from 100 MeV to 100 GeV and compared it with X-ra…
Evaluation of saltwork ponds operation through brine characterization and geochemical modelling using PHREEQC code integrating the Pitzer correction
2021
Seawater represents a potential resource for the extraction of salts and raw materials [1]. About one-third of the global table-salt production is manufactured in solar saltworks [2], being the most representative product of seawater processing. However, other valuable compounds such as Magnesium, Lithium and trace elements belonging to the alkaline/alkaline-earth metals (e.g. Rb, Cs, Sr) and transition/post-transition metals (e.g. Co, Ga, Ge) are present. Many of these elements are included in the EU Critical Raw Materials (CRM) list, grouping natural assets classified as fundamental for the wealth of the socio-economic structure of Europe [3]. In saltworks, natural evaporation of seawater…