The effect of pressure on the solubility of minerals in water and seawater

The effect of presure on the solubility of minerals in water and seawater can be estimated from In

$\text{(}\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^0{}_{\mathrm{sp}}\text{) +}\text{(?ΔVP + 0.5ΔKP}{}^2\text{)}\text{RT}$

where the volume (ΔV) and compressibility (ΔK) changes at atmospheric pressure (P = 0) are given by

$\text{ΔV =}\text{V}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{V}\text{?}\text{[MX(s)]ΔK =}\text{K}\text{?}\text{(M}{}^{\mathrm{+}}\text{, X}{}^{\mathrm{?}}\text{) ?}\text{K}\text{?}\text{[MX(s)]}$

Values of the partial molal volume ($\text{V}\text{?}$) and compressibilty ($\text{K}\text{?}$) in water and seawater have been tabulated for some ions from 0 to 50°C. The compressibility change is quite large (~10 × 10^?3 cm³ bar^?1 mol^?1) for the solubility of most minerals. This large compressibility change accounts for the large differences observed between values of ΔV obtained from linear plots of In K_sp versus P and molal volume data (Macdonald and North, 1974; North, 1974). Calculated values of $\text{K}{}^{\mathrm{P}}{}_{\mathrm{sp}}\text{K}{}^{\mathrm{o}}{}_{\mathrm{sp}}$ for the solubility of CaCO₃, SrSO₄ and CaF₂ in water were found to be in good agreement with direct measurements (Macdonald and North, 1974). Similar calculations for the solubility of minerals in seawater are also in good agreement with direct measurements (Ingle, 1975) providing that the surface of the solid phase is not appreciably altered.     

Salting-out of methane in single-salt solutions at 25°C and below 800 psia

Aqueous solubilities of methane at 25°C have been determined in single-salt solutions equilibrated with a CH₄ gas phase at 350, 550, and 750 psia. Measurements were made over a range of ionic strengths in NaCl, KCl, CaCl₂, MgCl₂, Na₂SO₄, K₂SO₄, MgSO₄, Na₂CO₃, K₂CO₃, NaHCO₃, and KHCO₃ aqueous solutions.At 25°C and constant pressure and methane fugacity, methane solubilities were largely controlled by the stoichiometric ionic strength, I, and the cation of the salt. Except for an increased salting-out due to HCO₃^?, the anion effect was relatively insignificant. Different but consistent solubility trends were followed in monovalent and divalent cation salt solutions as a function of I. Solubilities increased in salt solutions having a common anion in the following cation sequence: Na⁺ < K⁺ ? Ca²⁺ < Mg²⁺.The molal salting coefficient, k_m, for each salt was constant under the experimental conditions of the study, k_m is defined by $\text{log}\text{γ}\text{ch}{}_4\text{I}$ where $\text{γ}\text{ch}{}_4$, the molal activity coefficient, is the methane solubility ratio () measured at constant temperature, pressure, and CH₄ fugacity. Single-salt k_m values are as follows: 0.121, NaCl (4m); 0.121, Na₂SO₄ (1m); 0.118, Na₂CO₃ (1.5m); 0.146, NaHCO₃ (0.5m); 0.101, KCl (4m); 0.108, K₂SO₄ (0.5m); 0.111, K₂CO₃ (2m); 0.145, KHCO₃ (0.5m); 0.071, CaCl₂ (2m); 0.063, MgCl₂ (2m); and 0.066, MgSO₄ (1.5m) where the molalities in parentheses refer to the maximum salt concentrations used in this study.     

Constantes de formation des complexes hydroxydés de l'aluminium en solution aqueuse de 20 a 70°C

Stability constants of hydroxocomplexes of Al(III):Al(OH)²⁺ and A1(OH)₄^? have been measured in the 20–70°C temperature range by reactions involving only dissolved species. The stability constant ${}^1\text{K}{}_1$ of the first complex ion is studied by measuring pH of solutions of aluminium salts at several concentrations. ${}^1\text{β}{}_4$ of aluminate ion is deduced from equilibrium constants of the reaction between the trioxalato aluminium (III) complex ion and Al³⁺ in acid medium, and between the same complex ion and A1(OH)₄^? in alkaline medium. The K values and the associated ΔH are ${}^1\text{K}{}_1\text{= 10}{}^{\mathrm{?5.00}}$ and ΔH₁ = 11.8 Kcal; ${}^1\text{β}{}_4\text{= 10}{}^{\mathrm{?22.20}}$ and ΔH₄ = 42.45 Kcal. These last results are not in agreement with the values of recent tables for $\text{ΔG}{}^0\text{?}$ and $\text{ΔH}{}^0\text{?}$ of Al³⁺ and Al(OH)₄^?. We suggest a consistent set of data for dissolved and solid Al species and for some aluminosilicates.     

Effet de la température sur les distributions de Na,Rb et Cs entre la sanidine,la muscovite,la phlogopite et une solution hydrothermale sous une pression de 1 kbar

The distribution of trace amounts of Na, Rb and Cs, between muscovite, phlogopite, sanidine and hydrothermal solution have been studied by ion exchange in a temperature range from 400 to 800°C.These distributions have been expressed with a partition ratio P^aq?m_x = $\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{aq}}\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{m}}$ (where X is Na, Rb or Cs).In the case of Na and Cs in muscovite, even for the dilute solutions, the ratio P^aq?m_x is not the equilibrium constant k_x of exchange reactions. In other cases, P^aq?m_x does not depend on the trace alkali ion concentration in silicates (X) and is equal to k_x. Variations of P_x or k_x with T are greater for Na and Cs than for Rb. Generally, k_x decreases with increase in T. The function log $\text{P}{}_{\mathrm{x}}\text{= f(}\text{1}\text{T}\text{)}$ is not linear for Na or Cs, but in the case of Rb, $\text{f(}\text{1}\text{T}\text{)}$ is linear and the standard enthalpy and entropy of exchange reactions have been estimated by applying the Arrhenius relation.The distribution relations obtained between silicate and vapour phase permit the determination of distributions of Na, Rb and Cs between two minerals mI and mII, relative to K. These have been expressed with the partition ratio Q_x =$\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{mI}}\text{(}\text{X}\text{K}\text{)}{}^{\mathrm{mII}}$. Variations of Q_x with T are not remarkable, and even for Rb between phlogopite and feldspar are negligible. Nevertheless, one may use the distributions of Rb and Cs between muscovite and feldspar for geothermometry. Experimental results have been applied to some rocks by effecting corrections from the major element composition of the natural minerals. Estimated temperatures are near to 400°C in the granites and pegmatite studied here.     

The ionization of acids in estuarine waters

The stoichiometric, $\text{K}{}_{\mathrm{HA}}{}^1$, and apparent, K'_HA, constants for the ionization of a number of weak acids (NH₄⁺, HSO₄^?, HF, H₂O, B(OH)₃, H₂CO₃, HCO₃^?, H₃PO₄, H₂PO₄^?, HPO₄², H₃AsO₄ H₂AsO₄^? and HAsO₄^2?) in seawater at 25°C diluted with water have been fitted to equations of the form (Millero, 1979). In $\text{K}{}_{\mathrm{HA}}{}^1\text{= In K}{}_{\mathrm{HA}}\text{+ AS}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ BS}$ where In K_HA is the thermodynamic constant in water, S is the salinity, A and B are adjustable parameters. The validity of this equation in estuarine waters has been examined by using an ion pairing model (Millero and Schreiber, 1981). The calculated values of $\text{K}{}_{\mathrm{HA}}{}^1$ and K'_HA at S = 35%. are in good agreement with the measured values for all the systems examined. The equation used to extrapolate the measured values to pure water K_HA predicted values that agreed with those determined by using the ion pairing model. The exception was the ionization of HPO₄^2? due to the strong interactions of Ca²⁺ and Mg²⁺ with PO₄^3?. The differences in the predicted values of $\text{K}{}_{\mathrm{HA}}{}^1$ in seawater diluted with pure water and average river water were very small for all the acids except HPO₄^2? (the maximum ΔpK = 0.96 in average river water). The larger difference in the $\text{K}{}_{\mathrm{HA}}{}^1$ for HPO₄^2? in river waters is due to the strong interactions of Ca²⁺ and PO₄^3?.     

The thermodynamics of the carbonate system in seawater

The apparent constants (K'_i) for the ionization of carbonic acid in seawater at various salinities (S,%.) have been fit to equations of the form ln $\text{K'}{}_{\mathrm{i}}\text{= ln K}{}_{\mathrm{i}}\text{+ A}{}_{\mathrm{i}}\text{S}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+ B}{}_{\mathrm{i}}\text{S}$whereK_i is the thermodynamic ionization constant in water, A_i, and B_i are adjustable parameters. The temperature dependence (TK) of K_i, A_i and B_i were of the form, a₀ + a₁/T + a₃ ln T. Equations of similar forms have been used to analyze the ionization constants for water and boric acid and the solubility product of calcite in seawater. The effect of pressure on the apparent constants ($\text{K}{}^{\mathrm{p}}{}_{\mathrm{i}}\text{K}{}^{\mathrm{o}}{}_{\mathrm{i}}$) have been fit to equations of the form ln $\text{(}\text{K}{}^{\mathrm{p}}{}_{\mathrm{i}}\text{K}{}^{\mathrm{o}}{}_{\mathrm{i}}\text{) = ? (ΔVP + 0.5 ΔK P}{}^2\text{)/RT}$ where the volume (ΔV) and compressibility (ΔK) changes are polynomial functions of temperature. The equations generated for various açids in seawater have been used to examine the carbonate system in seawater. Equations relating the NBS and Tris pH scales have been derived as well as equations of pH as a function of temperature and pressure. The equations from Hansson (1972, Ph.D. Thesis, University of Göteborg, Sweden) and Mehrbachet al. (1973, Limnol. Oceanogr.18, 897–907) have been used to examine the components of the carbonate system. At a fixed total alkalinity and total carbon dioxide, differences of ±0.01 m-equiv kg^?1 in HCO^?₃ and CO^2?₃ were found; however, the [CO₂] and P_co2 are nearly the same. The contribution of borate ion, B(OH)^?₄ determined from the equations of Hansson (1972, Ph.D. Thesis, University of Göteborg, Sweden) and Lyman (1957, Ph.D. Thesis, University of California, Los Angeles) differ by ±0.01 m-equiv kg^?1 for waters with the same salinity and temperature.     

Gibbsite solubility and thermodynamic properties of hydroxy-aluminum ions in aqueous solution at 25°C

Solubility curves were determined for a synthetic gibbsite and a natural gibbsite (Minas Gerais, Brazil) from pH 4 to 9, in 0.2% gibbsite suspensions in 0.01 M NaNO₃ that were buffered by low concentrations of non-complexing buffer agents. Equilibrium solubility was approached from oversaturation (in suspensions spiked with Al(NO₃)₃ solution), and also from undersaturation in some synthetic gibbsite suspensions. Mononuclear Al ion concentrations and pH values were periodically determined. Within 1 month or less, data from over-and undersaturated suspensions of synthetic gibbsite converged to describe an equilibrium solubility curve. A downward shift of the solubility curve, beginning at pH 6.7, indicates that a phase more stable than gibbsite controls Al solubility in alkaline systems. Extrapolation of the initial portion of the high-pH side of the synthetic gibbsite solubility curve provides the first unified equilibrium experimental model of Al ion speciation in waters from pH 4 to 9.The significant mononuclear ion species at equilibrium with gibbsite are Al³⁺, AlOH²⁺, Al(OH)⁺₂ and Al(OH)^?₄, and their ion activity products are $\text{1K}{}_{50}\text{= 1.29 × 10}{}^8$, $\text{1K}{}_{\mathrm{s1}}\text{= 1.33 × 10}{}^3$, $\text{1K}{}_{\mathrm{s2}}\text{= 9.49 × 10}{}^{\mathrm{?3}}$ and $\text{1K}{}_{\mathrm{s4}}\text{= 8.94 × 10}{}^{\mathrm{?15}}$. The calculated standard Gibbs free energies of formation (ΔG°_f) for the synthetic gibbsite and the A1OH²⁺, Al(OH)⁺₂ and Al(OH)^?₄ ions are ?276.0, ?166.9, ?216.5 and ?313.5 kcal mol^?1, respectively. These ΔG°_f values are based on the recently revised ΔG°_f value for Al³⁺ (?117.0 ± 0.3 kcal mol_?1) and carry the same uncertainty. The ΔG°_f of the natural gibbsite is ?275.1 ± 0.4 kcal mol^?, which suggests that a range of ΔG°_f values can exist even for relatively simple natural minerals.     

The chemistry of geothermal waters in Iceland. III. Chemical geothermometry in geothermal investigations

New data from geothermal wells in Iceland have permitted empirical calibration of the chalcedony and $\text{Na}\text{K}$ geothermometers in the range of 25–180°C and 25–250°C respectively. The temperature functions are:

$\text{t°C=}\text{1112}\text{4.91?}\text{log SiO}{}_2\text{?273.15}$

$\text{t°C=}\text{933}\text{0.993+}\text{log Na/K}\text{?273.15}$

Concentrations are expressed in ppm. These temperature functions correspond well with the chalcedony solubility data of Fournier (1973) and the thermodynamic data for low-albite/microcline/solution equilibria of Heloeson (1969).A new CO₂ geothermometer is proposed which is considered to be useful in estimating underground temperatures in fumarolic geothermal fields. Its application involves analysis of CO₂ concentrations in the fumarole steam. The temperature function which applies in the range 180?300°C is: logCO₂ = 37.43 + 73192/T- 11829· 10₃/T² + 0.18923T- 86.187·logT where T is in °K and CO₂ in moles per kg of steam.     

Carbonate equilibria in hydrothermal systems: First ionization of carbonic acid in NaCl media to 300°C

The ionization quotients of aqueous carbon dioxide (carbonic acid) have been precisely determined in NaCl media to 5 m and from 50° to 300°C using potentiometric apparatus previously developed at Oak Ridge National Laboratory. The pressure coefficient was also determined to 250°C in the same media. These results have been combined with selected information in the literature and modeled in two ways to arrive at the best fits and to derive the thermodynamic parameters for the ionization reaction, including the equilibrium constant, activity coefficient quotients, and pressure coefficients. The variation with temperature of the two fundamental quantities $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ and $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ were examined along the saturation vapor pressure curve and at constant density. The results demonstrated again that for reactions with minimal electrostriction changes the magnitudes and variations of $\text{Δ}\text{C}\text{?}{}^{\mathrm{o}}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}{}^{\mathrm{o}}$ with temperature are small and, in addition, $\text{Δ}\text{C}\text{?}{}_{\mathrm{p}}$ and $\text{Δ}\text{V}\text{?}$ are approximately independent of salt concentration.The results have also been applied to an examination of the solubility of calcite as a function of pH (in a given NaCl medium) for the neutral to acidic region both for systems with fixed CO₂ pressure and systems where the calcium ion concentration equals the concentration of carbon. The pH of saturated solutions of calcite with P_CO2 of 12 bars increases from 5.1 to 5.5 between 100° and 300°C.     

Matrix corrections in trace-element analysis by X-ray fluorescence: An extension of the Compton scattering technique to long wavelengths

Mass absorption coefficients (A₂) for a series of standard rocks, have been calculated in the wavelength region 0.492–3.03 $\text{a}\text{?}$. Plots of these data against the intensity of the Compton scattered peak [(I) Compton] give an excellent correlation for the wavelengths 0.429 $\text{a}\text{?}$ to the Fe-absorption edge (1.74 $\text{a}\text{?}$); the data confirm the observations of Reynolds. Hence, routine measurement of one peak will give the mass absorption coefficient of a sample in an analytically important region (Sn/1bK_α to Ni/1bK_α). A₂ has also been directly measured on three of the samples and systematic differences between calculated and measured are attributed to the measuring technique. At wavelengths longer than the Fe-absorption edge, (up to 3.03 $\text{a}\text{?}$) A₂ can be estimated using a combination of (I) Compton and Fe/1bK_α c.p.s. This technique enables meaningful matrix corrections to be carried out on the elements Co, Mn, Cr, V, Ti, Sc (K spectra) and Ba (L spectra). Cr and Ba results are presented for some standard rocks.     

Kiglapait geochemistry V: Strontium

The Kiglapait intrusion contains 330 ppm Sr and has $\text{Sr}\text{Ca}\text{= 5 × 10}{}^{\mathrm{?3}}$ and $\text{Rb}\text{Sr}\text{= 3 × 10}{}^{\mathrm{?3}}$, as determined by summation over the Layered Group of the intrusion. Wholerocks in the Lower Zone contain 403 F_L^0.141 ppm Sr, where F_L is the fraction of liquid remaining; Sr drops to 180 ppm at the peak of augite production (F_L = 0.11) and rises to a maximum of 430 ppm in the Upper Zone before decreasing to 172 ppm at the end of crystallization. Feldspars in the Lower Zone contain 532 F_L^0.090 ppm Sr, increasing to 680 ppm in the Upper Zone before decreasing to 310 ppm at the end. Clinopyroxenes contain 15 to 30 ppm Sr and have a mineral-melt distribution coefficient D = 0.06 except near the top of the intrusion where D = 0.10.The calculated feldspar-liquid distribution coefficient has an average value near 1.75 but shows four distinct trends when plotted against X_An of feldspar. The first two of these are strongly correlated with the modal augite content of the liquid, on average by the relation D = 1.4 + 0.02 Aug^L. The third (decreasing) trend is due to co-crystallization of apatite, and the fourth (increasing) trend can best be attributed to a triclinic-monoclinic symmetry change in the feldspar at An₂₆, 1030°C. The compound feldspar-liquid distribution coefficient K_D for $\text{Sr}\text{Ca}$ bears out these deductions in detail and yields ΔG_r for the Sr-Ca exchange ranging from nearly zero at the base of the Lower Zone to ?26 kJ/gramatom at the end of crystallization. The compound feldspar-liquid distribution coefficient K_D for $\text{Rb}\text{Sr}$ varies from 0.3 in the Lower Zone to 1.1 at the end of crystallization.The ratio $\text{Ca}{}^{\mathrm{F}}\text{Ca}{}^{\mathrm{L}}$ is about 1.45 for troctolitic liquids containing 5% augite, for which K_D (Sr-Ca) = 1.0 and D_Ca = D_Sr. For common basaltic liquids containing 20% augite, the Kiglapait data predict $\text{solSr}{}^{\mathrm{F}}\text{Sr}{}^{\mathrm{L}}\text{= 1.8}$, as commonly found elsewhere. The strong dependence of D_sr on augite content of the liquid illuminates the role of liquid composition and structure in determining the feldspar-liquid distribution coefficient. Conversely, a discontinuous change in the trend of D_Sr when apatite arrives shows that the effect is due to apatite crystallization itself, not to the continuous variation of the liquid as it becomes enriched in apatite component.     

Alkali differentiation in LL-chondrites

The LL-group chondrites Krähenberg (Krbg) and Bhola are heterogeneous agglomerates containing a variety of lithic fragments and chondrules as well as crystal fragments. The $\text{Fe}\text{Fe}$ + Mg content of most olivine grains is uniform (Fa₂₈), although a few with distinctly lower Fe contents were found (Fa₁₉). Both meteorites contain large, cm-sized, fragments with high enrichments of K (~12×), Rb (~45×) and Cs (~70×) relative to LL-chondrites, while the REE concentrations are normal (except for a negative Eu anomaly); Na and Sr are depleted (~0.5×) and the $\text{Na}\text{K}$ weight ratio is 0.33 compared to 11 in the host. However, there is no difference in the sum of Na + K atoms. Also, the major elements, Si, Al, Mg, Ca and Fe, are nearly the same in fragments as in the host material. The K-rich igneous lithic fragments have a microporphyritic texture of euhedral to skeletal olivines in a partly devitrified glass with ~4% K₂O. The main pans of both Krbg and Bhola contain mesostasis glasses in porphyritic chondrules and lithic fragments with varying K content (0.1–8.6% K₂O) and $\text{Na}\text{K}$ ratios (0.2–100). Crystalline plagioclase is depleted in K with an average $\text{Na}\text{K}$ ratio of 22, i.e. higher than that for ordinary chondritic plagioclase, 8.4. Olivines in the large, K-rich fragments and in the host meteorites have the same iron content (Fa₂₈), indicating that both formed under the same oxygen fugacity and probably on the same parent body.Conceivable mechanisms for the formation of the K-rich rocks from normal LL-chondrite parent material are: 1, magmatic differentiation: 2. Na-K exchange via a vapor phase; 3. silicate liquid immiscibility; 4. volatilization and condensation in impact events. Process 2 appears most feasible for forming a rock enriched only in K and heavier alkalies and depleted in Na without noticeably changing other elements including the REE.     

Enthalpy of formation of forsterite,enstatite, akermanite,monticellite and merwinite at 1073 K determined by alkali borate solution calorimetry

Enthalpies of solution of synthetic enstatite (Mg₂Si₂O₆), forsterite (Mg₂SiO₄), akermanite (Ca₂MgSi₂O₇), monticellite (CaMgSiO₄), and merwinite (Ca₃MgSi₂O₈) and their component oxides were determined in eutectic (Li, Na)BO₂ at 1073 K. Resulting enthalpies of formation at 1073 are enstatite: $\text{?8.10 ± 0.42}\text{kcal}$; forsterite: $\text{?14.23 ± 0.45}\text{kcal}$; akermanite: $\text{?42.60 ± 0.39}\text{kcal}$; monticellite: $\text{?25.05 ± 0.41}\text{kcal}$; and merwinite: $\text{?51.10 ± 0.49}\text{kcal}$. The value for the synthetic monticellite of composition Mo_.965Fo_.035 was corrected slightly for non-stoichiometry based on experimental monticellite-forsterite phase equilibrium relations.The enthalpies of formation of enstatite and forsterite are somewhat less negative than yielded by several other solution calorimetric studies but are in good agreement with the recent Pb₂B₂O₅ solution calorimetry of Kiselevaet al. (1979), and are in good agreement with values to be derived from reliable phase equilibrium data in the system MgO-Al₂O₃-SiO₂. The enthalpies of formation of akermanite, monticellite and merwinite are all much less negative than values tabulated by robieet al. (1978) and helgesonet al. (1978) but are shown to be compatible with reliable phase equilibrium data for the system CaO-MgO-SiO₂, whereas the tabulated values are not. Several methods of analysis yield an entropy of monticellite at 1000 K of $\text{69.9 ± 0.2 cal/K}$.     

Density calculations for silicate liquids. I. Revised method for aluminosilicate compositions

Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature T_r, is given by $\text{V}{}_{\mathrm{r}}\text{= ∑X}{}_{\mathrm{i}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{i}}\text{+ X}{}_{\mathrm{A}}\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$, where the summation is taken over all oxide components except A1₂O₃, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is the composition-dependent apparent partial molar volume of Al₂O₃. The thermal expansion coefficient of aluminosilicate liquids is given by $\text{α = ∑X}{}_{\mathrm{i}}\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}\text{+ X}{}_{\mathrm{A}}\text{}\text{?}\text{ga}{}_{\mathrm{A}}{}^{\mathrm{o}}$, where $\text{}\text{?}\text{ga}{}_{\mathrm{i}}{}^{\mathrm{o}}$ terms are constants independent of temperature and composition, and $\text{}\text{?}\text{ga}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is a composition-dependent term representing the effect of Al₂O₃ on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V(T) = V_rexp[α(T-T_r)], where T_r = 1400°C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 $\text{cc}\text{mole}$ and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of $\text{V}\text{?}{}^{\mathrm{o}}{}_{\mathrm{A}}$ is discussed in terms of several possible interpretations of the structural role of Al³⁺ in aluminosilicate melts.     

An ion-association model for PbO-SiO2 melts: interpretation of thermochemical,conductivity, and density data

We propose that within PbO-SiO₂ melts the component species PbO(1) and SiO₂(1) associate to form a lead orthosilicate complex [Pb₂SiO₄(1)] according to $\text{2PbO(1) + SiO}{}_2\text{(1)}\text{a}\text{?}\text{f Pb}{}_2\text{SiO}{}_4\text{(1)}$ The association constant (K) for the above reaction is near 30 at 900 and 1000°C On the premises that the enthalpy of the above reaction is the only contributor to the enthalpy of mixing and that three melt species [PbO(1), SiO₂(1), Pb₂SiO₄(1)] mix ideally (Raoult's Law obeyed), the partial molar properties and the integral mixing properties of the melt have been calculated and have been found to accurately reproduce the measured thermochemical data.The conductivity data and density data for PbO-SiO₂ melts have been calculated using the association model. The calculated data again are remarkably consistent with the experimental data.Other silicate-melt models have been reinterpreted and that of Toop and Samis is compatible with the proposed model. In fact the Toop and Samis model implicitly assumes the formation of orthosilicate species rather than condensed polymeric species.     

The effect of pressure on the ionization of boric acid in sodium chloride and seawater from molal volume data at 0 and 25°C

The apparent molal volume, φ_V of boric acid, B(OH)₃ and sodium borate, NaB(OH)₄, have been determined in 35%. salinity seawater and 0·725 molal NaCl solutions at 0 and 25°C from precise density measurements. Similar to the behavior of nonelectrolytes and electrolytes in pure water, the φ_V of B(OH)₃ is a linear function of added molality and the φ_V of NaB(OH)₄ is a linear function of the square root of added molarity in seawater and NaCl solutions. The partial molal volumes, $\text{V}\text{?}\text{1}$, of B(OH)₃ and NaB(OH)₄ in seawater and NaCl were determined from the φ_V's by extrapolating to infinite dilution in the medium. The $\text{V}\text{?}\text{1}$ of B(OH)₃ is larger in NaCl and seawater than pure water apparently due to the ability of electrolytes to dehydrate the nonelectrolyte B(OH)₃. The $\text{V}\text{?}\text{1}$ of NaB(OH)₄ in itself, NaCl and seawater is larger than the expected value at 0·725 molal ionic strength due to ion pair formation [Na⁺ + B(OH)₄^? → NaB(OH)₄⁰]. The volume change for the formation of NaB(OH)₄⁰ in itself and NaCl was found to be equal to 29·4 ml mol^?1 at 25°C and 0·725 molal ionic strength. These large $\text{Δ}\text{V}\text{?}\text{1}$'s indicate that at least one water molecule is released when the ion pair is formed [Na⁺ + B(OH)₄^? → H₂O + NaOB(OH)₂⁰]. The observed $\text{V}\text{?}\text{1}$ in seawater and the $\text{Δ}\text{V}\text{?}\text{1}$ (NaB⁰) in water and NaCl were used to estimate $\text{Δ}\text{V}\text{?}\text{1 (MgB}{}^{\mathrm{+}}\text{) = Δ}\text{V}\text{?}\text{1 (CaB}{}^{\mathrm{+}}\text{) = 38·4 ml mol}{}^{\mathrm{?1}}$ for the formation of MgB⁺ and CaB⁺. The volume change for the ionization of B(OH)₃ in NaCl and seawater was determined from the molal volume data. Values of $\text{Δ}\text{V}\text{?}\text{1 = ?29·2 and ?25·9 ml mol}{}^{\mathrm{?1}}$ were found in seawater and $\text{Δ}\text{V}\text{?}\text{1 = ?21·6 and ?26·4}$ in NaCl, respectively, at 0 and 25°C. The effect of pressure on the ionization of B(OH)₃ in NaCl and seawater at 0 and 25°C determined from the volume change is in excellent agreement with direct measurements in artificial seawater (culberson and Pytkowicz, 1968; Disteche and Disteche, 1967) and natural seawater (Culberson and Pytkowicz, 1968).     

Use of Pitzer's equations to determine the media effect on the formation of lead chloro complexes

The spectrophotometric measurements of chloro complexes of lead in aqueous HCl, NaCl, MgCl₂ and CaCl₂ solutions at 25°C have been analyzed using Pitzer's specific interaction equations. Parameters for activity coefficients of the complexes PbCl⁺, PbCl₂⁰ and PbCl₃^? have been determined for the various media. Values of $\text{K}{}_1\text{= 30.0 ± 0.6}$, $\text{K}{}_2\text{= 106.7 ± 2.1}$ and $\text{K}{}_3\text{= 73.0 ± 1.5}$ were obtained for the cumulative formation constants. [$\text{Pb}{}^{\mathrm{2+}}\text{+ nCl}{}^{\mathrm{?}}\text{→ PbCl}{}_{\mathrm{n}}{}^{\mathrm{2?n}}\text{)}$]. These values are in reasonable agreement with literature data. The Pitzer parameters for the PbCl ion pairs in various media were used to calculate the speciation of Pb²⁺ in an artificial seawater solution.     

Petrochemical constraints on the models of Cretaceous-Eocene tectonic evolution of the Eastern Pontic chain (Turkey)

Sixteen selected samples from the Upper Cretaceous volcanic belt of the Eastern Pontids have been analysed for major elements, Rb, Sr and Zr. On the basis of the K₂O versus SiO₂ distribution, two groups of rocks have been distinguished, one with calc-alkaline affinity and a second group with shoshonitic character. The calc-alkaline rocks have porphyritic texture with clinopyroxene, plagioclase and orthopyroxene as phenocryst and in the groundmass. The orthopyroxene is lacking in the shoshonites where plagioclase, clinopyroxene and, in the more evolved terms, amphibole and biotite are the main phenocryst minerals. The shoshonitic rocks have higher $\text{K}{}_2\text{O}\text{Na}{}_2\text{O}$ ratio, K₂O, P₂O₅ and Rb, contents with respect to the calc-alkaline samples. The TiO₂ content is invariably low, never exceeding approximately 1%. The occurrence of volcanic rocks ranging in composition from calc-alkaline to shoshonitic in the Upper Cretaceous volcanic belt of the Eastern Pontids suggests that the Upper Cretaceous volcanic cycle reached its mature stage before the onset of the Eocene calc-alkaline volcanism which is believed to be neither genetically nor tectonically related with the Upper Cretaceous volcanism.     

The solubilities of calcite,aragonite and vaterite in CO2-H2O solutions between 0 and 90°C,and an evaluation of the aqueous model for the system CaCO3-CO2-H2O

Calculations based on approximately 350 new measurements (Ca_T-PCO₂) of the solubilities of calcite, aragonite and vaterite in CO₂-H₂O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants K_C, K_A, and K_V respectively, for the reaction CaCO₃(s) = Ca²⁺ + CO^2?₃: $\text{Log K}{}_{\mathrm{C}}\text{= ?171.9065 ? 0.077993T +}\text{2839.319}\text{T}\text{+ 71.595 log T}$$\text{Log K}{}_{\mathrm{A}}\text{= ?171.9773 ? 0.077993T +}\text{2903.293}\text{T}\text{+71.595 log T}$$\text{Log K}{}_{\mathrm{V}}\text{= ?172.1295 ? 0.077993T +}\text{3074.688}\text{T}\text{+ 71.595 log T}$ where T is in ^oK. At 25°C the logarithms of the equilibrium constants are ?8.480 ± 0.020, ?8.336 ± 0.020 and ?7.913 ± 0.020 for calcite, aragonite and vaterite, respectively.The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO⁺₃ and CaCO⁰₃ ion pairs, revised analytical expressions for CO₂-H₂O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO₂-dependence if the CaHCO⁺₃ association constant is between 0 and 90°C, corresponding to the value logK_Cahco⁺3 = 1.11 ± 0.07 at 25°C. The CaCO⁰₃ association constant was measured potentiometrically to be between 5 and 80°C, yielding logK_CaCO⁰3 = 3.22 ± 0.14 at 25°C.The CO₂-H₂O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of K_H, K₁ and K₂ are $\text{log K}{}_{\mathrm{H}}\text{= 108.3865 + 0.01985076T ?}\text{6919.53}\text{T}\text{? 40.45154 log T +}\text{669365.}\text{T}{}^2$, $\text{log K}{}_1\text{= ?356.3094 ? 0.06091964T +}\text{21834.37}\text{T}\text{+ 126.8339 log T —}\text{1684915.}\text{T}{}^2$ and logK₂ = ?107.8871 ? 0.03252849T + 5151.79/T + 38.92561 logT ? 563713.9/T² which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures.Extensive measurements of the pH of Ca-HCO₃ solutions at 25°C and 0.956 atm PCO₂ using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH.Earlier arguments suggesting that the CaHCO⁺₃ ion pair should not be included in the CaCO₃-CO₂-H₂O aqueous model were based on less accurate calcite solubility data. The CaHCO⁺₃ ion pair must be included in the aqueous model to account for the observed PCO₂-dependence of aragonite solubility between 317 ppm CO₂ and 100% CO₂.Previous literature on the solubility of CaCO₃ polymorphs have been critically evaluated using the aqueous model and the results are compared.