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1.
Francesco Crea Alba Giacalone Antonio Gianguzza Daniela Piazzese Silvio Sammartano 《Marine Chemistry》2006,99(1-4):93
In this paper SIT and Pitzer models are used for the first time to describe the interactions of natural and synthetic polyelectrolytes in natural waters. Measurements were made potentiometrically at 25 °C in single electrolyte media, such as Et4NI and NaCl (for fulvic acid 0.1 < I /mol L− 1 < 0.75), and in a multi-component medium simulating the composition of natural waters at a wide range of salinities (for fulvic and alginic acids: 5 < S < 45) with particular reference to sea water [Synthetic Sea Water for Equilibrium studies, SSWE]. In order to simplify calculations, SSWE was considered to be a “single salt” BA, with cation B and anion A representing all the major cations (Na+, K+, Mg2+, Ca2+) and anions (Cl−, SO42−) in natural sea water, respectively. The ion pair formation model was also applied to fulvate and alginate in artificial sea water by examining the interaction of polyanions with the single sea water cation. Results were compared with those obtained from previous speciation studies of synthetic polyelectrolytes (polyacrylic and polymethacrylic acids of different molecular weights). Results indicate that the SIT, Pitzer and Ion Pairing formation models used in studies of low molecular weight electrolytes may also be applied to polyelctrolytes with a few simple adjustments. 相似文献
2.
The hydrolysis of silicic acid, Si(OH)4, was studied in a simplified seawater medium (0.6 M Na(Cl)) at 25°C. The measurements were performed as potentiometric titrations (hydrogen electrode) in which OH− was generated coulometrically. The total concentration of Si(OH)4, B, and log[H+] were varied within the limits 0.00075 B 0.008 M and 2.5 -log[H+] 11.7, respectively. Within these ranges the formation of SiO(OH)3− and SiO2(OH)22− with formation constants log β−11(Si(OH)4 SiO(OH)3− + H+) = −9.472 ±0.002 and log β−21(Si(OH)4 SiO2(OH)22− + 2H+) = −22.07 ± 0.01 was established. With B > 0.003 M polysilicate complexes are formed, however, with -log[H+] 10.7 their formation does not significantly affect the evaluated formation constants. Data were analyzed with the least squares computer program LETAGROPVRID. 相似文献
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4.
The interactions of Fe(II) and Fe(III) with the inorganic anions of natural waters have been examined using the specific interaction and ion pairing models. The specific interaction model as formulated by Pitzer is used to examine the interactions of the major components (Na+, Mg2+, Ca2+, K+, Sr2+, Cl−, SO4−, HCO3−, Br−, CO32−, B(OH)4−, B(OH)3 and CO2) of seawater and the ion pairing model is used to account for the strong interaction of Fe(II) and Fe(III) with major and minor ligands (Cl−, SO42−, OH−, HCO3−, CO32− and HS−) in the waters. The model can be used to estimate the activity and speciation of iron in natural waters as a function of composition (major sea salts) and ionic strength (0 to 3 M). The measured stability constants (KFeX*) of Fe(II) and Fe(III) have been used to estimate the thermodynamic constants (KFeX) and the activity coefficient of iron complexes (γFeX) with a number of inorganic ligands in NaClO4 medium at various ionic strengths: In(KFeX/γFeγX) = InKFeX − In(γFeX) The activity coefficients for free ions (γFe, γx) needed for this extrapolation have been estimated from the Pitzer equations. The activity coefficients of the ion pairs have been used to determine Pitzer parameters (BFeX, BFeX0, CFeXφ) for the iron complexes. These results make it possible to estimate the stability constants for the formation of Fe(II) and Fe(III) complexes over a wide range of ionic strengths and in different media. The model has been used to determine the solubility of Fe(III) in seawater as a function of pH. The results are in good agreement with the measurements of Byrne and Kester and Kuma et al. When the formation of Fe organic complexes is considered, the solubility of Fe(III) in seawater is increased by about 25%. 相似文献
5.
P. Lpez 《Estuarine, Coastal and Shelf Science》2003,56(5-6):943-956
The effect of a sudden increase in salinity from 10 to 37 in porewater concentration and the benthic fluxes of ammonium, calcium and dissolved inorganic carbon were studied in sediments of a small coastal lagoon, the Albufera d'Es Grau (Minorca Island, Spain). The temporal effects of the changes in salinity were examined over 17 days using a single diffusion-reaction model and a mass-balance approach. After the salinity change, NH4+-flux to the water and Ca-flux toward sediments increased (NH4+-flux: 5000–3000 μmol m−2 d−1 in seawater and 600/250 μmol m−2 d−1 in brackish water; Ca-flux: −40/−76 meq m−2 d−1 at S=37 and −13/−10 meq m−2 d−1 at S=10); however, later NH4+-flux decreased in seawater, reaching values lower than in brackish water. In contrast, Ca-flux presented similar values in both conditions. The fluxes of dissolved inorganic carbon, which were constant at S=10 (55/45 mmol m−2 d−1), increased during the experiment at S=37 (from 30 mmol m−2 d−1 immediately after salinity increase to 60 mmol m−2 d−1 after 17 days).In brackish conditions, NH4+ and Ca2+ fluxes were consistent with a single diffusion-reaction model that assumes a zero-order reaction for NH4+ production and a first-order reaction for Ca2+ production. In seawater, this model explained the Ca-flux observed, but did not account for the high initial flux of NH4+.The mass balance for 17 days indicated a higher retention of NH4+ in porewater in the littoral station in seawater conditions (9.5 mmol m−2 at S=37 and 1.6 mmol m−2 at S=10) and a significant reduction in the water consumption at both sites (5 mmol m−2 at S=37; 35/23 mmol m−2 at S=10). In contrast, accumulation of dissolved inorganic carbon in porewater was lower in seawater incubations (−10/−1 meq m−2 at S=37; 50/90 meq m−2 at S=10) and was linked to a higher efflux of CO2 to the atmosphere, because of calcium carbonate precipitation in water (675/500 meq m−2). These results indicate that increased salinity in shallow coastal waters could play a major role in the global carbon cycle. 相似文献
6.
Sorption of yttrium and rare earth elements by amorphous ferric hydroxide: Influence of pH and ionic strength 总被引:1,自引:0,他引:1
The sorption of yttrium and the rare earth elements (YREEs) by amorphous ferric hydroxide at low ionic strength (0.01 M ≤ I ≤ 0.09 M) was investigated over a wide range of pH (3.9 ≤ pH ≤ 7.1). YREE distribution coefficients, defined as iKFe = [MSi]T / (MT[Fe3+]S), where [MSi]T is the concentration of YREE sorbed by the precipitate, MT is the total YREE concentration in solution, and [Fe3+]S is the concentration of precipitated iron, are weakly dependent on ionic strength but strongly dependent on pH. For each YREE, the pH dependence of log iKFe is highly linear over the investigated pH range. The slopes of log iKFe versus pH regressions range between 1.43 ± 0.04 for La and 1.55 ± 0.03 for Lu. Distribution coefficients are well described by an equation of the form iKFe = (Sβ1[H+]− 1 + Sβ2[H+]− 2) / (SK1[H+] + 1), where Sβn are stability constants for YREE sorption by surface hydroxyl groups and SK1 is a ferric hydroxide surface protonation constant. Best-fit estimates of Sβn for each YREE were obtained with log SK1 = 4.76. Distribution coefficient predictions, using this two-site surface complexation model, accurately describe the log iKFe patterns obtained in the present study, as well as distribution coefficient patterns obtained in previous studies at near-neutral pH. Modeled log iKFe results were used to predict YREE sorption patterns appropriate to the open ocean by accounting for YREE solution complexation with the major inorganic YREE ligands in seawater. The predicted log iKFe′ pattern for seawater, while distinctly different from log iKFe observations in synthetic solutions at low ionic strength, is in good agreement with results for natural seawater obtained by others. 相似文献
7.
The effect of ionic interactions on the kinetics of disproportionation of HO2, and the oxidation of Fe(II) and Cu(I) has been examined. The interactions of O2 with Mg2+ and Ca2+ ions in seawater increases the lifetime by 3–5 times compared to water. The effect of OH− on the oxidation of Fe(II) in water and seawater shows a second degree dependence from 5 to 45°C. The effect of salinity on the oxidation of Fe(II) was found to be independent of temperature, while the effect of temperature was found to be independent of salinity. The energy of activation for the overall rate constant was found to be 7 ± 0.5 kcal mol−1.The effect of pH, temperature, salinity and ionic composition on the oxidation of Cu(I) has also been examined. In NaCl solutions from 0.5 to 6 M, the log k for the oxidation was a linear function of pH (6–8) with a slope of 0.2 ± 0.05. The reaction was strongly dependent on the Cl− concentration with variation of
from 0.3 to 340 min from 0.5 to 6 M Cl−. The rates of oxidation of Cu+ and CuCl0 responsible for these effects are dependent upon ionic strength. The energy of activation for the reaction was 8.5–9.9 kcal mol−1 from 0.5 to 6 M. Studies of the oxidation in various NaX salts (X = I−, Br− and Cl−) give rates in the order Cl− > Br− > I− as expected, due to complex formation of Cu+ with X−. 相似文献
8.
Effects of irradiance on benthic and water column processes in a Gulf of Mexico estuary: Pensacola Bay, Florida, USA 总被引:1,自引:0,他引:1
Michael C. Murrell Jed G. Campbell James D. Hagy III Jane M. Caffrey 《Estuarine, Coastal and Shelf Science》2009,81(4):501-512
We examined the effect of light on water column and benthic fluxes in the Pensacola Bay estuary, a river-dominated system in the northeastern Gulf of Mexico. Measurements were made during the summers of 2003 and 2004 on 16 dates distributed along depth and salinity gradients. Dissolved oxygen fluxes were measured on replicate sediment and water column samples exposed to a gradient of photosynthetically active radiation. Sediment inorganic nutrient (NH4+, NO3−, PO43−) fluxes were measured. The response of dissolved oxygen fluxes to variation in light was fit to a photosynthesis–irradiance model and the parameter estimates were used to calculate daily integrated production in the water column and the benthos. The results suggest that shoal environments supported substantial benthic productivity, averaging 13.6 ± 4.7 mmol O2 m−2 d−1, whereas channel environments supported low benthic productivity, averaging 0.5 ± 0.3 mmol O2 m−2 d−1 (±SE). Estimates of baywide microphytobenthic productivity ranged from 8.1 to 16.5 mmol O2 m−2 d−1, comprising about 16–32% of total system productivity. Benthic and water column dark respiration averaged 15.2 ± 3.2 and 33.6 ± 3.7 mmol O2 m−2 d−1, respectively Inorganic nutrient fluxes were generally low compared to relevant estuarine literature values, and responded minimally to light exposure. Across all stations, nutrient fluxes from sediments to the water column averaged 1.11 ± 0.98 mmol m−2 d−1 for NH4+, 0.58 ± 1.08 mmol m−2 d−1 for NO3−, 0.01 ± 0.09 mmol m−2 d−1 for PO43−. The results of this study illustrate how light reaching the sediments is an important modulator of benthic nutrient and oxygen dynamics in shallow estuarine systems. 相似文献
9.
The rates of the reduction of Cr(VI) with S(IV) were measured in deaerated NaCl solution as a function of pH, temperature and ionic strength. The rates of the reaction were found to be first order with respect to Cr(VI) and second order with respect to S(IV), in agreement with previous results obtained at concentrations two order higher than the present study. The reaction also showed a first-order dependence of the rates on the concentration of the proton and a small influence of temperature with an apparent energy of activation ΔHapp of 22.8 ± 3.4 kJ/mol. The rates were independent of ionic strength from 0.01 to 1 M. The rate of Cr(VI) reduction is described by the general expression
−d[Cr(VI)]/dt=k[Cr(VI)][S(IV)]2