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1.
The stability constants of the ion pairs NaSO4?, KSO4?, MgSO4?, CaSO4, MgCl+ and CaCl+ were determined at 25°C and 0.7 M formal ionic strength, by measuring the solubility of gypsum (CaSO4 · 2H2O) in different media. The media used contained one or two of the following electrolytes: NaCl, KCl, MgCl2, NaClO4, Mg(ClO4)2, Na2SO4. Values for the stability constants are 1.22, 1.84, 12.3, 30.6, 0.48 and 1.20 M?1, respectively, and the solubility product for gypsum is 2.87 · 10?4M2. The distribution of the main constituents of seawater was calculated using these results and the values of the carbonate and bicarbonate constants given by Dyrssen and Hansson (1972–1973). The solubility of gypsum in seawater as calculated and determined experimentally was 21.43 mM and 21.10 mM, respectively.  相似文献   

2.
The conditional stability constant of HSO4? has been determined at 25°C, 1 atm and a formal ionic strength of 0.7 M in solutions containing sodium, magnesium, chloride and sulphate. This was done spectrophotometrically (UV), using diphenylamine as indicator. The value obtained was 17.0 ± 0.1 (molar scale). Single ion activity coefficients for Na2SO4, K2SO4 and MgSO4 have been calculated according to the Bates et al. (1970) model, assuming that the sulphate ion is not hydrated. It was found that the single ion activity coefficient of sulphate changes very little between Na2SO4, K2SO4 and MgSO4 when the formal ionic strength is kept constant.These results have been used to obtain relations between the stability constants of NaSO4? and MgSO4 valid for seawater.  相似文献   

3.
The stability constants K1 and K12 of phosphoric acid were determined for artificial seawater of six different salinities (5, 10, 20, 30, 35, 40‰) and in 0.2, 0.4 and 0.7 M NaCl at three temperatures (5, 15, 25°C). The results are compared with those of Kester and Pytkowicz (1967), Atlas et al. (1976) and Dickson and Riley (1979). The ionic product of water, Kw, was determined in sodium chloride media at 5, 15 and 25°C. Complex formation among Ca2+, Mg2+, HPO42? and PO43? is discussed.  相似文献   

4.
Various investigators reported a decrease in pH as seawater is concentrated. A similar phenomenon was reported for Dead Sea waters which are about ten times more saline than seawater. The reasons for the low pH values of Dead Sea waters (pH 5.9–6.5), which precipitate CaCO3, were investigated by determining the apparent dissociation constants of carbonic acid in these brines. A new method, based on alkalinity titration and least-squares fitting, was used to estimate the proton activity coefficient (γH+) and the first and second dissociation constants of carbonic acid (K1′, K2′) in natural and artificial Dead Sea waters. It was found that as the salt content increases, pK′1 and pK′2 values progressively decrease whereas γH+ sharply increase. At the highest salinity investigated (TDS = 330 gl?1) γH+ pK′1 and pK′2 values are 24.5, 5.09 and 6.23, respectively, as compared to about 0.8, 5.9, 9.1 respectively for normal seawater (19‰ chlorinity) at the same temperature (30°C).The implication of the results of this study regarding solubility of CaCO3 and the general behavior of the carbonate system in hypersaline solutions is discussed.  相似文献   

5.
Spectrophotometric measurements are reported for the first apparent dissociation constant of hydrogen sulfide in seawater over the temperature range 7.5–25°C and 2–35.8‰ salinity. These data are described by the expression pK1′ = 2.527 ? 0.169 Cl13 + 1359.96/T. The second apparent dissociation constant in potassium chloride solution was estimated potentiometrically using a sulfide specific ion electrode. A value of ～13.6 was found for pK2′ at a KCl concentration of 0.67 M. It is suggested that explicit reference to the sulfide ion, S2?, in describing equilibria in marine waters be dropped in favor of a formulation involving the bisulfide ion, HS?.  相似文献   

6.
The thermodynamics and kinetics of the H2S system in natural waters have been critically reviewed. Equations have been derived for the solubility and ionization of H2S in water and seawater as a function of salinity, temperature and pressure. Pitzer parameters for the interaction of the major cations (Na+, Mg2+ and Ca2+) with HS− have been determined to allow one to calculate values of pK1* in various ionic media. The limited data available for the interaction of trace metals for HS− are summarized and future work is suggested.The kinetics of oxidation of H2S have also been examined as a function of pH, temperature, and salinity. The discrepancies in the available data are largely due to the different [O2]/[HS−] ratios used in various studies. Over a limited pH range (6–8) the pseudo first order rate constant for the oxidation is shown to be directly proportional to the activity of HS−. Further studies are suggested to examine the effect of ionic media and temperature on the rate of oxidation.  相似文献   

7.
Hydration, ion-water interactions, and water structure effects in seawater were studied by determining differences (Δβ) between the compressibilities of test salt solutions and the compressibilities of reference solutions. The reference solutions were distilled water and seawater (35%0), and the test salt solutions were either 0.13 m or 0.26m with respect to one of the following test salts: LiCl, NaCl, KCl, CsCl, NaF, NaI, MgCl2, CaCl2, BaCl2, Na2SO4, K2SO4, and MgSO4. The compressibility measurements (to 900 bars) were carried out at 2°C and also at 15°C using a differential method in which a pressure increase or a temperature increase causes Δβ to become less negative. At 1 bar and 15°C, the Δβ (0.26 m, distilled water reference) values ranged from ?1.14 × 10?6 bar? for NaI to ?3.84 × 10?6 bar?1 for Na2SO4, and the Δβ (0.26 m, seawater reference) values ranged from ?1.30 × 10?6 bar?1 for NaCl to ?3.04 × 10?6 bar?1 for Na2SO4. The Δβ values were used to calculate hydration numbers. Entropy of transfer, excess hydrogen bond breaking (determined by NMR), and effective radii of ions are properties which can be used to describe the influence of ions on water structure. The extent to which these properties correlate with Δβ values depends upon whether the ion is an anion or a cation, and this correlation forms the thesis that anions alter water structure in a different way than do cations.  相似文献   

8.
The activity of NaCl in artificial seawater was measured potentiometrically with Na+- and Cl? -sensitive electrodes. The salinity of the solutions, examined at 25°C, ranged from 10–40‰ salinity. The change in the activity from 5–25°C was measured at 35‰ salinity.The molal mean activity coefficient of NaCl in 35‰ seawater at 25°C is 0.667. The relative partial molal enthalpy of NaCl in 35‰ seawater is ?130 ±50 cal mol?1. This value is in good agreement with the value measured in pure 0.72 M NaCl.The results were compared with activity coefficients predicted by a specific interaction model and by an ion association model. Good agreement was found in both cases.  相似文献   

9.
The formation of the ion pairs MgSO4 and NaSO4? was investigated calorimetrically at 0.75 M ionic strength, 25°C, 1 atm. Simultaneous determinations of enthalpy changes, ΔH10, and stability constants, K1, were not possible, and values of K1 determined independently had to be introduced for the calculation of ΔH10. The values of ΔH10 obtained were 1–3 kJ mol?1 for MgSO4 and 0 kJ mol?1 for NaSO4?.  相似文献   

10.
The stability of the ion pair NaSO4 was determined by measuring the change in sodium activity with medium composition at constant ionic strength, using a sodium-sensitive glass electrode. The stability constants of MgSO4 and MgCl+ were determined indirectly from measurements of the stability of MgF+ in different media. All measurements were performed at 1 atm pressure, 25 ± 0.1 °C and 0.7 M formal ionic strength. The stability constants for NaSO4?, MgSO4, MgF+ and MgCl+ are 1.8 ± 0.1, 6.3 ± 0.1, 22.9 ± 0.1 and 0.34 ± 0.02 M?1, respectively.  相似文献   

11.
Distribution coefficients, iKFe, were measured for sorption of yttrium and the rare earth elements (YREEs) on hydrous ferric oxide (HFO) in 0.5 M NaCl solutions over the pH range 3.9–8.4 (T = 25 °C). An existing, non-electrostatic model [Quinn, K.A., Byrne, R.H., Schijf, J., 2006. Sorption of yttrium and rare earth elements by amorphous ferric hydroxide: influence of pH and ionic strength. Mar. Chem. 99, 128–150] was modified to account for sorption of YREE–chloride complexes, as well as YREE–hydroxide complexes at elevated pH. The extended model, which allows calculation of iKFe as a function of [H+], contains two parameters, SK1 and SK2, to describe the equilibrium between positive, neutral, and negative forms of the hydroxyl functional groups on the HFO surface. In addition, it contains several composite, conditional stability constants, An, that represent YREE bonding to the neutral groups with release of n protons and/or to the negatively charged groups with release of n ? 1 protons.In 0.5 M NaCl solutions, YREE sorption on HFO is weaker and less pH dependent, yielding only 0.7–0.9 protons per YREE cation on average, vs. about 1.5 at low ionic strength. This is due to enhanced deprotonation of the HFO surface (SK1 ~ 0, pSK2 = 6.16), leading to an increase in the proportion of negatively charged groups, which release fewer protons per YREE cation sorbed. On a logarithmic scale, iKFe is a nearly linear function of pH, except at pH > 8 where cumulative sorption of YREE–hydroxide complexes causes it to rise more rapidly, especially for the heavy REEs. Both our own data and prior results from the literature are well described by the extended model, using only three adjustable parameters, A1–A3. The constant A3, representing YREE bonding to the negatively charged groups with release of two protons, shows an excellent linear free-energy relation when plotted against the first YREE hydrolysis constant, β1*. There is no evidence for YREE bonding to the positively charged groups (i.e., A0 = 0).  相似文献   

12.
The apparent solubility product of aragonite in 32‰ seawater at 25.0°C is reported as K′sp = (0.869±0.049) × 10?6(mol2kgseawater?2) thus confirming the value of R.A. Berner, 1976 (Am. J. Sci., 276: 713–730). The apparent solubility product ratio for aragonite and calcite is reported as K′aragoniteK′calcite = 2.05 The deviation of this value from the thermodynamic ratio is atttributed to the formation of a stable low Mg-calcite coating on pure calcite in seawater measurements of solubility.  相似文献   

13.
The rate of iron(II) oxidation in North Sea water of pH 5.5–10 in the range 10–25°C has been studied. The oxygenation rate depends linearly on the iron(II) and dissolved oxygen concentrations. The second-order dependence on [OH?], found by several investigators for synthetic solutions, was confirmed in seawater, but only for pOH > 6.9. For pOH < 5.9 the rate appeared to be independent of the pOH. In the intermediate range, pOH 5.9–6.9, corresponding to the natural pH of seawater, a first-order dependence on the pOH is obeyed. The important discrepancy in the literature between the second-order rate constant for NaCHO3 solutions and for seawater can be attributed predominantly to the incorrect assumption of a second-order pOH dependence in natural seawater. The results can be useful, for example, in predicting the effect of dumping acidic iron waste from the titanium-dioxide industry into the ocean.  相似文献   

14.
The dissociation constants (pK1 and pK2) for methionine have been measured in artificial seawater as a function of salinity (S = 5 to 35) and temperature (5 to 45 °C). The seawater pK2 values were lower than the values in NaCl at the same ionic strength while the pK1 values in seawater were lower only at S = 35. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been used to determine the formation of Mg2+ complexes and Pitzer interaction parameters for Mg2+ with methionine. The seawater model with the interaction parameters accounts for the differences between the value of pK1 and pK2 between NaCl and seawater. This study demonstrates that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.  相似文献   

15.
A. V. Savenko 《Oceanology》2014,54(2):170-172
The solubility of amorphous silica was studied in mixtures of riverine and marine waters simulating the water composition at the river-sea geochemical barrier. The value of the thermodynamical equilibrium constant was determined for the reaction of silicon solubility as K r 0 = (1.71 ± 0.01) × 10?3 at 22°C. A near-linear dependence was found for the activity ratio of the H4SiO 4 0 and the salinity with the increase of this ratio from 1.00 in the riverine to 1.15 in the standard seawater.  相似文献   

16.
The precision of spectrophotometric measurements of indicator absorbance ratios is sufficient to allow evaluation of small isotopically induced differences in the dissociation constant of boric acid (KB). The quotient of 11KB and 10KB, obtained using isotopically ⩾99% pure borate/boric acid buffers, provides an equilibrium constant for the reaction 10B(OH)3+11B(OH)4−⇔11B(OH)3+10B(OH)4− which heretofore had not been experimentally determined. Previous theoretical and semi-empirical evaluations of this equilibrium, which is important for assessments of the paleo-pH of seawater and the paleo-pCO2 of the atmosphere, have yielded constants, 11–10KB=10KB/11KB, that have ranged between 1.0194 and approximately 1.033. The experimentally determined value 11–10KB=1.0285±0.0016 (mean±95% confidence interval) obtained at 25 °C and 0.63 molal (mol kg−1 H2O) ionic strength is in much better agreement with recent theoretical assessments of 11–10KB that have ranged between 1.026 and 1.033, than the much-cited original estimate (1.0194) of Kakihana et al. (1977) [Fundamental studies on the ion-exchange separation of boron isotopes. Bulletin of Chemical Society of Japan 50, 158–163]. Since the activity quotient for the fractionation reaction is almost equal to unity, it is expected that the 11–10KB value obtained in this study will be applicable over a wide range of solution compositions and ionic strengths.  相似文献   

17.
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   

18.
Abstract

The water chemistry, flora, and fauna of Lake Rotokawa (38° 37.8’ S, 176° 11.2'E) was studied in 1975–76. The mean pH is 2.1 and thermal inflows may elevate the mean summer temperature of the surface waters 4.2°c above that of nearby cold water Lake Rotongaio (18.9°c). The temperature range of surface water was from 10.1 °c in winter to 23.1°c in summer. The major anions were SO4 2? 679 g.m?3, and Cl‐ 314 g.m?3. Mean concentrations of major cations were Na+ 224 g.m?3, K+ 28.9 g.m?3, Ca2+ 13.3 g.m?3, and Mg2+ 2.6 g.m?3.

Two species of flagellate algae were recorded, of which Euglena anabaena was predominant. Only two benthic macroinvertebrates were found, larvae of Chironomus zealandicus, mean density 253 per square metre, and Helobdella sp., 1.3 per square metre.

The Parariki Stream was influenced by thermal springs in its upper and lower reaches, being cooler (24–25°c) about halfway along its length than near its source (27.8–39.0°c) or confluence (26.5°‐28.0°c) with the Waikato River. In the cooler stretch of the stream where unidentified benthic algae were not limited by high temperature, chlorophyll and total pigment increased from 3.9 to 377.9 mg.m?3 and from 17.5 to 534.4 mg.m?3 respectively, and nutrient levels fell (NO3‐N, 22–10.5 mg.m?3; NH4‐N, 6440–230 mg.m?3; and PO4‐P, 51–19 mg.m?3).  相似文献   

19.
Interaction of 54Mn and 55(59)Fe with EDTA in seawater and NaCl solutions was investigated by high-voltage paper electrophoresis. These two radionuclides were chosen because they represent two modes of behaviour of radionuclides in seawater—EDTA systems. In seawater without EDTA or at low EDTA concentrations in the systems 54Mn behaves as a cation while 55(59)Fe gives a zone at the starting point of the electrophoretic strip. At higher EDTA concentrations, both radionuclides give only one anionic zone showing complexing with EDTA. In the intermediate range of the EDTA concentration (“transition region”) 54Mn shows continuous change of the electrophoretic mobility from cationic to anionic (fast rate of interaction with EDTA), while 55(59)Fe reacts very slowly giving two well-separated zones in the transition region of the EDTA concentration.EDTA concentrations were varied from 10?6 to 10?2M, pH being adjusted to 8.0. The behaviour of radionuclides was followed by measuring the electrophoretic mobilities of radionuclides in dependence on the EDTA concentration at different aging times from 0 to 7 days.From the experimental data effective stability constants and the number of EDTA-ligands of 54MnEDTA and 55(59)FeEDTA complexes in seawater and 0.55 M NaCl solutions were calculated.  相似文献   

20.
A novel technique to determine complexing capacities for zinc is presented. The free zinc concentration is determined by cathodic stripping voltammetry preceded by adsorptive collection of complexes of zinc with ammonium pyrrolidine dithiocarbamate (APDC). The reduction peak of zinc is depressed as a result of ligand competition by natural organic material in the sample. Sufficient time is allowed to reach equilibrium between this material and added APDC, and equilibrium is maintained during the measurement. Both electrochemically reversible and irreversible complexes can therefore be investigated. Values for KZnAPDC′ are calibrated against NTA and EDTA in seawater of several salinities; log KZnAPDC′ was found to be 4.40 at 36‰, 4.36 at 24‰, 4.43 at 12‰, and 4.87 at 2.3‰. The ligand concentration and conditional stability constant, KZnL′, for complexing ligands in a sample from the Irish Sea were determined in the presence of 4 × 10?5 M APDC and with added zinc concentrations between 5 × 10?9 and 3 × 10?7 M. The data best fitted a complexation model containing two ligands with concentrations of 2.6 and 6.2 and 10?8 M, and with values for log KZnL′ of 8.4 and 7.5, respectively. These results are comparable to those obtained with other equilibrium techniques, but the values of the constants are greater than those from ASV measurements.  相似文献   

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