Measured and Predicted Solubility Phase Diagrams of Quaternary Systems LiBr-NaBr-MgBr 2 -H 2 O and LiBr-KBr-MgBr 2 -H 2
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doi: 10.1007/s40242-020-0154-7
Article
Measured and Predicted Solubility Phase Diagrams of Quaternary Systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K CUI Ruizhi1,2*, LI Wu1,2, DONG Yaping1,3 and LI Jun1,2 1. Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, P. R. China; 2. Key Laboratory of Salt Lake Resources Chemistry of Qinghai Province, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, P. R. China; 3. Qinghai Engineering and Technology Research Center of Comprehensive Utilization of Salt Lake Resources, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining 810008, P. R. China Abstract The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr 2·6H2O formed. In addition to this double salt, the three single salts LiBr∙2H 2O, KBr and MgBr2∙6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer’s electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones. Keywords Brine; Solubility; Phase diagram; Bromide; Pitzer’s model
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Introduction
Qinghai, located in western China, is rich in brine resources in its oil and gas field, as well as in salt lake. The oil and gas field brine belongs to calcium chloride type and contains many effective elements, such as lithium, potassium, boron, bromine, iodine, strontium, and thorium, which is known as an important liquid mineral resource. The comprehensive development is urgently needed for the development of the national economy. Brine is a naturally occurring multi-component system of salt and water. Experimental and theoretical phase equilibrium studies, as well as relevant thermodynamic properties, of brine systems are the focus and basic contents of salt mine geochemistry. The compositions of oil and gas field brine in Nanyishan region of Qinghai show that the complex brine system can be represented as Na-Cl-Ca-K-B4O7-Mg-Li-Sr-Br-H2O system. In the previous works, solid-liquid phase equilibrium of
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