Solid-liquid Equilibria In The Quinary Systems Na⁺,K⁺,Mg²⁺,Sr²⁺//Cl^--H₂O At 348K

The Sr-rich brine resources in the of Sichuan Basin has excellent quality, high salinity, riched in potassium, magnesium, calcium, strontium, boron, halogen and other useful components. The effective development and utilization of the liquid mineral resources has a very important role on regional economic development. System of water and salt balance study has theoretical guidance significance for the utilized of the brine resources. According to the composition of the Sr-rich brine resources in the of Sichuan Basin, phase equilibria in the quinary systems Na+, K+, Mg2+, Sr2+//Cl-–H2O at 348 K and some subsystems were studied by isothermal solution saturation method. It included four ternary subsystems: MgCl2–SrCl2–H2O at 323 K, MgCl2–SrCl2–H2O, NaCl–SrCl2–H2O and KCl–SrCl2–H2O at 348 K, and three quaternary subsystems: NaCl–KCl–SrCl2–H2O, KCl–MgCl2–SrCl2–H2O and NaCl–MgCl2–SrCl2–H2O at 348 K. The solubilities and densities of the solution in these systems are determined experimentally. Using the experimental data, the phase diagrams of listed above systems are obtained. We also concluded and summarized the determination method of strontium ion concentration in the brine, and calculated ion concentration uncertainty by the capacity titration for determination of strontium in brine. This article used the capacity titration and ICP-OES and engages the method of combining analysis result is reliable and has good reproducibility.In the ternary system MgCl2–SrCl2–H2O at 323 K and 348 K, there are two single-salt crystallization regions, which are strontium chloride dihydrate(SrCl2·2H2O) and magnesium chloride hexahydrate(MgCl2·6H2O). Contrasted the phase diagrams of there two systems at 323 K and 348 K: the shape of phase diagrams are slimliar, the two ternary systems aere type of simple common-saturation, and without double salt and solid solution. In these phase diagrams of the ternary systems, it can be found that there were all in one eutectic point, two univariant curves and two regions of crystallization. Two salts solubility all increasing with the temperature rised, salt of the crystallization area with crystallization water are same, but the crystallization area size is different. Due to the same ion effect, MgCl2 has salting out effect for SrCl2. In the ternary system NaCl–Sr Cl2–H2O at 348 K,there are two single-salt crystallization regions are strontium chloride dihydrate(SrCl2·2H2O) and sodium chloride(NaCl).In the ternary system NaCl–SrCl2–H2O at 348 K,there are two single-salt crystallization regions are strontium chloride dihydrate(SrCl2·2H2O) and potassium chloride(KCl). Comparisons between the phase diagram of these four systems at different temperatures show that the crystallization forms have not changed but the size crystallization field have changed. The two ternary systems are type of simple common-saturation, and without double salt and solid solution. In these phase diagrams of the ternary systems, it can be found that there are all in one eutectic point, two univariant curves and two regions of crystallization.The quaternary system NaCl–KCl–SrCl2–H2O and NaCl–MgCl2–SrCl2–H2O at 348 K are simple common-saturation and no double salt and solid solution are found. In the phase diagram,the two quaternary systems at 348 K both have one invariant point, three univariant curve and three crystallization fields corresponding to sodium chloride(NaCl), potassium chloride(KCl) and strontium chloride dihydrate(SrCl2·2H2O), and in the second system, is sodium chloride(NaCl), magnesium chloride hexahydrate(MgCl2·6H2O) and strontium chloride dihydrate(SrCl2·2H2O).The quaternary system KCl–MgCl2–SrCl2–H2O at 348 K has a double salt and no solid solution is found. In the phase diagram, the quaternary system at 348 K have two invariant point, five univariant curve and four crystallization fields corresponding to potassium chloride(KCl), magnesium chloride hexahydrate(MgCl2·6H2O), strontium chloride dihydrate(SrCl2·2H2O) and double salt KCl·MgCl2·6H2O(Car). Potassium chloride(KCl) have larger crystallization field, whereas magnesium chloride hexahydrate(MgCl2·6H2O) has smaller crystallization field.The quinary system Na Cl–KCl–MgCl2–SrCl2–H2O at 348 K has a double salt and no solid solution was found. In the phase diagram,the quaternary system at 348 K has two invariant point, five univariant curve and four crystallization fields corresponding to potassium chloride(KCl), magnesium chloride hexahydrate(MgCl2·6H2O), strontium chloride dihydrate(SrCl2·2H2O) and double salt KCl·MgCl2·6H2O(Car). The phase diagram of the quinary system NaCl–KCl–MgCl2– SrCl2–H2O is similar to quaternary system KCl–MgCl2–SrCl2–H2O at 348 K.