The study identifies the role played by different components of natural aquatic systems on the poorly known geochemistry of antimony. Different chemical forms of antimony were measured in porewaters and sediments of two Sudbury lakes characterized by contrasting redox conditions at the sediment-water interface. In porewaters, Sb(III) was present under reducing conditions where it could exist as SbS2- according to thermodynamic calculations. Sb(V) was detected mainly under oxic and mildly reducing environments where its presence was attributed to the oxidizing effect of iron and manganese oxyhydroxides or to the slow kinetics of reduction by dissolved sulfide or possible complexation by it. A third form of Sb identified as refractory was obtained after UV irradiation of the water samples, suggesting an association of Sb to low molecular weight natural organic matter. The distribution of Sb in sediments of the two lakes revealed (through the comparison of profiles and statistical correlations) the importance of iron and manganese oxyhydroxides in controlling the behavior of Sb, particularly in the lake where the interface was clearly oxic. Porewater profiles indicate that the dissolution of manganese and iron oxyhydroxides under anoxic conditions leads to the simultaneous release of dissolved Sb previously sorbed onto those compounds. In reducing sediments, the control of the solubility of Sb by iron sulfides is suggested.

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The solubility of the aqueous system containing lithium, sodium, potassium, chloride, and borate ions and the densities, viscosities, refractive indexes, conductivities, and pH at 298.15 K of the system have been studied. On the basis of the Ja ˜neche index values, the phase diagrams of dry salt, sodium, and water of the system were plotted. The dry-salt phase diagram of the system includes two four-salt cosaturation points, five solubility isotherm curves, and four crystallization zones all saturated with sodium chloride corresponding to potassium chloride, lithium chloride monohydrate, borax, and lithium borate trihydrate. No solid solution and double salts were found. On the basis of Pitzer's semiempirical equation for a mixed aqueous electrolytic solution, the chemical equilibrium model of Harvie was used to fit the single-salt Pitzer parameters of lithium borate, β (0) , β (1) , and C φ and the triplet mixed parameters Ψ Li,Cl,B4O5(OH)4 , Ψ Li,K,B4O5(OH)4 , and Ψ Li,Na,B4O5(OH)4 in this system, which are not reported in the literature. The prediction of the solubilities of salts in the five-component system was then demonstrated. The calculated solubilities agree well with the experimental values.

The Pitzer thermodynamic model for liquid-solid equilibrium in the quinary system LiCl-NaCl-KCl-SrCl 2 -H 2 O at 298.15 K was constructed by selecting the proper parameters and standard chemical potential. The solubility data and water activity data of the systems SrCl 2 -H 2 O, NaCl-SrCl 2 -H 2 O, KCl-SrCl 2 -H 2 O, LiCl-SrCl 2 -H 2 O, and NaCl-KCl-SrCl 2 -H 2 O were used to evaluate the model. Good agreement between the calculated and experimental solubility data indicates that the model is reliable. The Pitzer model for the above system at 298.15 K was then used to calculate the component solubilities and conduct computer simulation of isothermal evaporation of the mother liquor for the oilfield brine in Nanyishan region of Qaidam Basin (China). The evaporation-crystallization route and order of salt precipitation, changes in concentration and precipitation of lithium, sodium, potassium, and strontium, and water activities during the evaporation process were demonstrated. The salts crystallized from the brine in the order : KCl, NaCl, SrCl 2 ·6H 2 O, SrCl 2 ·2H 2 O, and LiCl·H 2 O. The whole evaporation-crystallization process may consist of six stages. In each stage the variation trends for the relationships between ion concentrations or water activities and the evaporation ratio are different. This result of the simulation of brines can be used as a theoretical reference for comprehensive exploitation and utilization of this type of brine resources.

The solubility and the physicochemical properties (density and refractive index) in the liquid–solid metastable system (KCl−CaCl2−H2O) at (288.15 and 308.15) K were determined using the isothermal evaporation method. Based on the experimental data, the metastable phase diagrams and the diagrams of physicochemical properties vs composition in the system at (288.15 and 308.15) K were plotted. In the metastable phase diagrams of the ternary system at (288.15 and 308.15) K, there are in all one invariant point, two univariant curves, and two crystallization zones, corresponding to potassium chloride, antarcticite (CaCl2·6H2O) at 288.15 K, and potassium chloride, and calcium chloride tetrahydrate (CaCl2·4H2O), at 308.15 K. This system at both temperatures belongs to a simple eutectic type, and neither double salts nor solid solution were found. Based on the extended Harvie−Weare (HW) models and temperature-dependent equations at (288.15 and 308.15) K, respectively, the values of the Pitzer parameters β(0), β(1),and C φ for KCl and CaCl2, the mixed ion-interaction parameters θK,Ca and ΨK,Ca,Cl, the Debye–Hückel parameter A φ, and the standard chemical potentials of the minerals in the ternary system were obtained by fitting. Using the temperature-dependent equations and the standard chemical potentials of the minerals respectively, the predictive solubilities for the ternary system at both temperatures are presented. A comparison between the calculated and experimental results at each temperature shows that the predicted solubilities obtained with the extended HW model agree well with experimental data.

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With the isothermal dissolution equilibrium method and wet-residue method, the solubility data as well as physicochemical properties including density, refractive index, and pH value of the two ternary systems (NaCl + NaBO 2 + H 2 O) and (Na 2 SO 4 + NaBO 2 + H 2 O) at 298.15 K and 0.1 MPa have been experimentally determined, and the relatively phase diagrams have been established for the first time. In the ternary system (NaCl + NaBO 2 + H 2 O), two invariant points, three univariant curves, and three crystallization regions corresponding to sodium chloride (NaCl), sodium metaborate tetrahydrate (NaBO 2 •4H 2 O), and a congruent double salt teepleite (NaCl•NaBO 2 •2H 2 O) were detected. While in the ternary system (Na 2 SO 4 + NaBO 2 + H 2 O), there are one invariant point, two univariant curves, and two crystallization regions corresponding to NaBO 2 •4H 2 O and mirabilite (Na 2 SO 4 •10H 2 O). The physicochemical properties (density, refractive index, and pH value) in the two systems present a regular variation versus that with the changes of sodium metaborate concentration in the solution. Moreover, on the basis their empirical equations, the calculated values of refractive index and density are consistent with the experimental data.

The metastable solubility of the reciprocal quaternary system containing sodium, potassium, chloride, and borate ions and the physicochemical properties corresponding to density, viscosity, pH value, and refractive index at 308.15 K have been studied with the isothermal evaporation method. According to the experimental data, the metastable equilibrium phase diagrams of dry salt and the water phase diagram of the system were plotted. In the dry-salt phase diagram, there are two invariant points, five univariant curves, and four crystallizing regions corresponding to sodium chloride, potassium chloride, borax (Na 2 B 4 O 7 · 10H 2 O), and potassium tetraborate tetrahydrate (K 2 B 4 O 7 · 4H 2 O). The crystallized region of borax is the largest, while the phase region of NaCl is the smallest with the highest concentration and a strong salting-out effect to borax. There are neither double salts nor solid solutions formed in the metastable system. When compared with the stable phase diagram at 298.15 K of the system, the areas of both metastable phase regions of borax and potassium chloride are enlarged, while other metastable phase regions are decreased. The calculated values of densities and refractive index in the metastable quaternary system with the empirical equations are in good agreement with the experimental values.