Volumetric Properties Of Subsystems Carbonate-type And Chloride-type Salt Lake Brines At Various Temperatures

The salt lakes on the Qinghai-Tibet Plateau are rich in resources and are famous for being rich in boron and lithium.According to composition of brine,the salt lakes can be divided into chloride type,sulfate type and carbonate type.Salt lake brine can be regarded as a complex electrolyte solution system.To develop and utilize salt lake resources,it is necessary to study various physical and chemical properties of brine,including the volume properties.The volume property is one of the most basic and important physical and chemical properties of the solution,which includes density,apparent molar volume,excess volume,and so on.Research on the volume properties of brine systems can not only provide basic data for the industrial production of salt lakes,but also help understand the physical and chemical phenomena that occur during the evaporation of brine and the interaction between solutes and water molecules in the solution.Because the composition of salt lake brine is very complex,it usually needs to be simplified into a multiple system for research.During the evaporation process,the ion composition and content of brine are not static,it is a dynamic process.Therefore,it is undoubtedly necessary to study the volume properties of different types of salt lake brines.In addition to experimental methods,modern electrolyte theory represented by the Pitzer ion interaction model has been successfully used in the study of the physical and chemical properties of natural water systems.According to the composition characteristics of carbonate and chloride salt lake brines in the Qinghai-Tibet Plateau and the temperature range involved in the natural evaporation of brines,a combination of experiment and Pitzer model was used to study the volume properties of Na–Cl–SO₄–CO₃–BO₂–H₂O and Na–K–Mg–Ca–Cl–H₂O systems from 293.15 K to 323.15 K.(1)The density of Na₂CO₃–H₂O?Na BO₂–H₂O?KCl–H₂O?Mg Cl₂–H₂O?Ca Cl₂–H₂O and Na₂B₄O₇–H₂O systems were measured from 293.15 K to 323.15 K with a high-precision oscillating tube density meter,the density decreases with the increase of temperature.Then the apparent molar volume and limit partial molar volume of the corresponding binary system are calculated according to the measured density.According to the calculation results,the apparent molar volume of the binary system changes with temperature and concentration,and the limit partial molar volume is analyzed and obtained.The results show that the binary systems are characterized by"structural destruction"between water molecules.Raman spectroscopy was used to study the effects of anions in the binary sub-systems of the Na–Cl–SO₄–CO₃–BO₂–H₂O system on the hydroxyl stretching spectrum of water.The results show that the anions in each solution have an effect on the microstructure of water.The influence is consistent with the calculated results of the volume properties.(2)The density of Na Cl–Na₂SO₄–H₂O,Na Cl–Na₂CO₃–H₂O,Na Cl–Na BO₂–H₂O,Na₂CO₃–Na BO₂–H₂O,Na₂SO₄–Na BO₂–H₂O,Na₂CO₃–Na₂SO₄–H₂O,KCl–Ca Cl₂–H₂O and Mg Cl₂–Ca Cl₂–H₂O systems were measured from 293.15 K to 323.15 K with a high-precision oscillating tube density meter.The relationship between the volume properties of the ternary system and the temperature and ionic strength is obtained.By calculating the excess volume of the ternary system before and after mixing,it is found The volume of ternary systems such as Na Cl–Na₂SO₄–H₂O and Na Cl–Na₂CO₃–H₂O all expand after being mixed.(3)According to the measured volume property data of the binary and ternary sub-systems studied above from 283.15 K to 323.15 K,fit the Pitzer ion interaction model to obtain the corresponding Pitzer single electrolyte parameters and mixing parameters.Using the obtained Pitzer parameters construct the volume properties model of two five-element systems from 283.15 K to 323.15 K,predict the density of Na–Cl–SO₄–CO₃–BO₂–H₂O and Na–K–Mg–Ca–Cl–H₂O at multiple temperatures.The predicted results are in good agreement with the experimental values,indicating that the Pitzer parameters obtained in this paper are reliable.The Pitzer model is suitable for the prediction of the volume properties of salt lake brine.