Study On The Phase Changes Of Water-salt Systems In Li-containing Salt Lake At Low Temperature

In this paper,the change of liquid phase composition and crystallization regularity of brine with different composition characteristics under natural and artificial cooling conditions are studied for salt lake brine containing Li⁺,Na⁺,K⁺,Mg²⁺,Cl^-,SO₄^2-at first.It provides theoretical guidance for the development of lithium-bearing salt lake technology at low temperature.In addition,Based on the NRTL model of electrolyte solution,the freezing point calculation model of water-salt system is established,and the freezing points of some binary and ternary water-salt systems containing the above components and the common binary and ternary water-salt systems are simulated and calculated and compared with the literature data.The results show that:?1?For the brines with the approximate concentrations,different cooling models have little effected on the change of liquid composition and crystallization regularity of the brine;for the brine with high concentration of sulfate,as fall of temperature,the sulfate content would reduce rapidly;for the brines with low sulfate and high lithium,as the temperature reduction,potassium chloride would crystallize out,and lithium be enriched;Compared with the normal temperature,the salt lake brine containing Li⁺,Na⁺,K⁺,Cl^-,SO₄^2-does not have crystals of double salts at low temperature.These works will provide a theoretical guidance to exploit the lake source at cool environment.?2?Based on the NRTL model of electrolyte solution,the freezing point calculation models are established,and the freezing points of binary water and salt system are calculated,and the results are satisfactory.For 1:1 type of water and salt system,the average relative deviation between the calculated freezing point and the experimental value is about 4%;For 1:2,2:1 and 2:2 binary water and salt systems,the deviation is slightly greater than 1:1 solution,especially for 2:2 MgSO₄ solution,the relative deviation is 22.4%.However,after adjusting the binary action parameters,the average relative deviation of MgSO₄ solution decreases to 5.72%.?3?The freezing points of six kinds of ternary water and salt systems,such as NaCl-KCl-H₂O,are calculated by using the established freezing point calculation model.For the ternary water and salt systems that charges'number are 1,the average relative deviation is about 5.94%,The maximum relative deviation is 7.475%and the deviation is not more than 1.834?;For the ternary water-salt systems that charges'number are greater than 1,the calculated results have a slightly larger deviation,the average relative deviation is about 14.94%,the maximum relative deviation is 31.84%.The total calculation results show that it is feasible to use the electrolyte solution NRTL model to predict the freezing point of the ternary water and salt system,and this model can play a guiding role in the prediction of the freezing point of the polybasic water and salt system.?4?The NRTL model of electrolyte solution is used to calculate the freezing point.The number of ion charges and binary energy interaction parameters are the main factors that affect the deviation of the results.The calculation deviation of high valence solution is larger than that of low valence solution.For the same water-salt system,the calculated results from different binary energy interaction parameters are different that compared by the experimental values.If the suitable binary interaction parameters are selected,the calculation results of freezing point are more ideal.