Characteristics Of Boron Isotopic Fractionation In The Process Of Evaporating And Salting Out Of The Dasugan Lake Water

The evaporation experiments of salt lake brine are mostly concentrated in the sulfate stage of chloride and magnesium,so it is difficult to obtain the law of salt evolution and p H value change in the whole salt lake evolution stage of carbonate sulfate chloride in the same system,and then analyze the characteristics of boron isotope fractionation in the evolution process of salt lake systematically.Based on this,this paper mainly focuses on the study of boron isotope fractionation in the process of evaporation and salting out of brackish water in the Dasugan Lake,involving the evaporation experiment of brine,the determination of boron isotope and the law of salt evolution,the change of p H value and boron isotope fractionation in the process of evaporation.The main research contents are summarized as follows:(1)The evaporation experiment was carried out in a constant temperature chamber at 28±2 ?,and the experimental design was divided into two groups: full separation of solid-liquid phase(CSE)evaporation and continuous deposition of solid phase(PCE)evaporation.In the evaporation process,41 liquid samples and 30 solid samples were collected.(2)The sequence of evaporating and salting out was as follows: calcite monohydrate-halite-nesquehonite-bloedite-epsomite-hexahydrite-burkeite.Based on the analysis of the ion concentration,p H value of the liquid phase and the XRD of the precipitated minerals in the evaporation process,the lake water of the Dasugan Lake was divided into three evolution stages of carbonate-sulfate-chloride in the evaporation and concentration process,and the law of salt evolution and p H value change in the evaporation and concentration of sodium sulfate sub type brackish water lake were clarified.Different from other sodium sulfate subtypes,mirabilite precipitation was not observed in the process of evaporation.The change of mineral phase affected the change of p H value.And the chemical behavior of potassium and boron in the evaporation process was explained.(3)The results of this experiment show that the change of mineral phase in the process of evaporating and salting out is the root cause of the change of boron distribution coefficient.The order of the influence of different minerals on boron distribution is: calcite monohydrate,nesquehonite,sulfate and halite.The boron isotopic fractionation coefficients of the lake water in the carbonate stage of evaporating and salting out were 0.9937 ? 1.0008(CSE)and 0.9964 ? 1.0001(PCE),respectively.Although there was no precipitation of calcium sulfate(such as gypsum)in the sulfate stage,the precipitation of magnesium sulfate(bloedite)also caused higher boron isotope fractionation.Due to the precipitation of sulfate in halite stage,there was also high boron isotope fractionation.The boron isotopic fractionation systems of sulfate and halite were 0.9944 ? 1.0017(CSE)and 0.9913 ? 0.9978(PCE).Based on the above research content,the research results of this paper have a more comprehensive understanding of the salt evolution law and the p H value change law in each salt evolution stage of sodium sulfate subtype brackish water lake,and have a positive significance for the study of boron isotope fractionation in the evolution process of brackish water and brine.