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The Pitzer equations have been used to fit the apparent molal adiabatic compressibility of electrolytes in water as a function of temperature. The equations have been used to estimate the partial molal compressibility for a number of cations and anions in 0.725 m NaCl and average seawater (S = 35 g kg–1). The calculated results for electrolytes are in good agreement with direct measurements in 0.725 m NaCl and seawater. The partial molal compressibilities estimated from the model can be used to make more reliable estimates of the effect of pressure on activity coefficients and ionic equilibria in seawater and other mixed electrolyte solutions at high pressures.

The apparent molal volumes (Vϕ) of the trivalent rare earth (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) chlorides, nitrates and perchlorates have been calculated from the density measurements at 25 °C and (5 to 80) °C and 0.02 – 4 m. The values of Vϕ have been fitted to the Pitzer equations, Vϕ = V0 + (AvI/(1.2m) ln(1 + 1.2I0.5) + 2RTm(βV(0) + βV(1) g(y) + mCV), where V0 is the infinite dilution partial molal volume, Av is the Debye- Huckel slope, I is the ionic strength, and g(y) = (2/y2)·[1 – (1 + y) exp(−y)] where y = 2(I0.5). The Pitzer volume parameters βV(0), βV(1) and CV are functions of temperature. The values of V0, βV(0), βV(1), and CV for most of the rare earth chlorides are similar orders of magnitude. These results should be useful in estimating the effect of pressure on the equilibria of rare earths in natural waters over a wide range of temperature.

The rates of thiourea oxidation with Fe(VI) were determined as a function of pH (8.8−11.5) and temperature (10−35 °C). The rate law for the oxidation of thiourea was found to be −d[Fe(VI)]/dt = k0{...

The TRIS buffer system is frequently used to calibrate electrodes and indicators that are used to determine the pH of natural waters. Most of the potentiometric and spectrophotometric systems used to measure the pH are calibrated with TRIS buffers. Since most natural waters contain high concentrations of NaCl, it is useful to be able to determine the pK of TRIS using ionic interaction models. In this paper, the dissociation constants of TRIS in NaCl solutions from (0 to 100) °C and (0 to 5) mol·kg−1 have been fitted to Pitzer equations. This allows one to estimate the values of the pH for TRIS buffers for natural brines over a wide range of conditions.

The rates of oxidation of hydrogen sulfide with Fe(VI) were made anaerobically as a function of pH (7−12) and temperature (5−15 °C). The reaction was found to be first order for each reactant. The rates decrease with an increase in pH. The energy of activation was found to be 30.1 ± 4.9 kJ mol-1 at pH = 12. When the concentrations of [H2S]T ([H2S] + [HS-]) are in excess, the ratio of [H2S]T consumed to [Fe(VI)] consumed was 1.51 ± 0.14 at pH = 7.0 and 2.50 ± 0.13 at pH = 9.0 and 11.3. Thiosulfate was the main product at pH = 7.0; sulfite, thiosulfate, and sulfate were identified as the products of the reactions at pH = 9.0 and 11.3. In an excess of [Fe(VI)] over [H2S]T, the hydrogen sulfide is fully oxidized to sulfate. A mechanism in which Fe(VI) oxidizes H2S by a one-electron process is proposed. Experiments were conducted to test the Fe(VI) removal efficiency of sulfide in groundwater and wastewater. The results indicate that Fe(VI) can be used as an effective oxidant to remove hydrogen sulfide from wa...

The adsorption of phosphate on manganese dioxide (δMnO2) was determined in seawater as a function of pH, temperature, and salinity. The adsorption in a simple electrolyte solution (0.7 M NaCl) was adequately fitted using the triple-layer surface complexation model, assuming that phosphate formed outer-sphere complexes on the surface of δMnO2. SO42- and humic acid were found to suppress the adsorption at low pH, but had no effect in the pH range of seawater. The addition of Ca2+ and Mg2+ in 0.7 M NaCl was found to enhance the adsorption of phosphate on δMnO2 at pH > 4. This increased adsorption might be due to the changes in both the surface charge of δMnO2 and the solution speciation of phosphate in the presence of Ca2+ and Mg2+. The results suggest that manganese oxides can act as important adsorbents of phosphate in natural waters, as well as in surface sediments, when they are present at higher concentrations than other reactive constituents, such as iron and aluminum oxides.

The apparent molal heat capacities (φCp) of 1−1 electrolytes at 25 °C have been fitted to the Pitzer equation φCp = Cp,2° + (AJ/1.2) ln(1 + 1.2I1/2) − 2RT2[mBJMX + m2CJMX], where Cp,2° is the partial molal heat capacity of at infinite dilution and BJMX and CJMX are empirical constants related to ion−ion interactions. The values of Cp,2° of the electrolytes have been used to determine partial molal heat capacities of ions. The coefficients BJMX and CJMX have been combined with Pitzer coefficients for enthalpies and osmotic coefficients to develop equations that can be used to determine activity coefficients of these electrolytes from 10 to 70 °C and from 0.1 to 2 m to within 1%.

The oxidation of Cu(I) in air-saturated solutions of sea water has been measured as a function of pH (5.3-8.6), temperature (5-45 /sup 0/C), and salinity (5-44). The overall rate constant k (kg mol/sup -1/ min/sup -1/) d(Cu(I))/dt = -k(Cu(I))(O/sub 2/) has been fitted to log k = 10.73 + 0.23 pH - 2373/T - 3.33I/sup 1/2/ + 1.45I with a standard error of 0.08 in log k. The energy of activation was found to be 45.6 +/- in 1.7 kJ mol/sup -1/. The strong chloride dependence of the rates has been attributed to the effect of temperature and ionic strength on the oxidation of Cu/sup +/ and CuCl/sup 0/ species. At a given Cl/sup -/ concentration, the rates of oxidation in sea water are lower than in NaCl or NaCl-NaClO/sub 4/ mixtures. These differences in sea water are due to a decrease in the rates due to Mg/sup 2 +/ and Ca/sup 2 +/ and the increase in the rates due to HCO/sub 3//sup -/. Possible causes of these effects are discussed.

Etude de l'oxydation de Cu(I) par O 2 dans les melanges NaX-NaClO 4 . Constantes de stabilite de CuI

The formation of H/sub 2/S occurs in a number of areas in natural waters.The production in pore waters and anoxic basins is due to biological processes while the production in hydrothermal systems is due to geochemical processes. At the interface between anoxic and oxic waters, large changes occur in the state of metals and nonmetals (1,2). This is due to the changes in the redox conditions, solubility conditions, and bacterial activity. Although one can question the importance of abiotic thermodynamic and kinetic processes at this interface, it is useful to use simple inorganic models to approximate the real system. Recently, researchers (3) have examined the thermodynamics and kinetics of the H/sub 2/S system in natural waters. From this review, it became apparent that large discrepancies existed in the rates of oxidation of H/sub 2/S in natural waters from various studies. Studies on the effect of various parameters such as temperature, salinity, and pH for seawater were nonexistent. In this paper data is presented on the oxidation of H/sub 2/S in water, seawater, and NaCl solutions as a function of temperature (5-65 /sup 0/C), pH (1-12), and ionic strength (I = 0-6 M). These results will hopefully fill some of themore » gaps and yield equations valid for most natural waters. 21 references, 8 figures, 4 tables.« less

for the reference salt, XaC1) show no sign of a discontinuity in the suspected range between 45" and 60°C. On the other hand, it is difficult to see how transitions from the low temperature legs of these curves can be made to the corresponding high temperature sections without multiple inflections or distinct discon- tinuities. These apparent inconsistencies are within the admitted uncertainty of the data above 120°C.

Discusses comparisons of packing densities derived from known molar volume data of liquids and solutions with packing densities that have been observed for assemblies of randomly packed spheres, an...