Stable isotope fractionation of chlorine during evaporation of brine from a saline lake  

作　　者：LUO ChongGuang XIAO YingKai MA HaiZhou MA YunQi ZHANG YanLing HE MaoYong 

机构地区：[1]CAS Key Laboratory of Salt Lake Resources and Chemistry,Qinghai Institute of Salt Lakes,Chinese Academy of Sciences,Xining 810008,China [2]State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710075,China [3]Graduate University,Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Chinese Science Bulletin》2012年第15期1833-1843,共11页

基　　金：supported by the National Basic Research Program of China (2011CB403000);the National Natural Science Foundation of China (40776071,40976074 and 41173019)

摘　　要：Brine from the saline Qarhan Lake was evaporated at 28±2°C in a clean environment.Two groups of experiments were conducted;one with complete separation of precipitate and brine at different stages of evaporation,and the other with continuous precipitation during the evaporation.Seventy-nine precipitate and brine samples were collected during the experiments,and the δ37 Cl values were determined using an improved thermal ionization mass spectrometry procedure for precise measurement of chlorine isotopes based on Cs2Cl+ ions.Based on the concentrations of Na+,K+,and Mg2+,evaporation was divided into three main precipitation stages as follows:halite dominant,carnallite dominant,and bischofite dominant.The δ37 Clsolid and δ37 Clliquid values of the precipitate and coexisting brine samples at different stages showed the following characteristics.The precipitates were enriched with 37 Cl relative to the coexisting brine samples,and the δ37 Cl of both the precipitate and brine samples decreased gradually during evaporation.The fractionation factors(αh) between halite and brine were the highest,followed by that(αc) between carnallite and brine,and then that(αb) between bischofite and brine.The αc and αb values of less than one,which indicate the precipitate is enriched in 35 Cl,were found when the evaporation process entered a new stage.However,the δ37 Cl values of carnallite,bischofite,and the coexisting brine samples decreased during evaporation.The residual brine is a 35 Cl reservoir.The experimental phenomena were consistent with the δ37 Cl values in saline deposits in the literature.δ37 Cl can be used as an indicator of brine evaporation processes,which is important in the exploration of sylvinite deposits.Brine from the saline Qarhan Lake was evaporated at 28±2 ℃in a clean environment. Two groups of experiments were conducted; one with complete separation of precipitate and brine at different stages of evaporation, and the other with continuous precipita- tion during the evaporation. Seventy-nine precipitate and brine samples were collected during the experiments, and the δ^37Cl values were determined using an improved thermal ionization mass spectrometry procedure for precise measurement of chlorine isotopes based on Cs2Cl^＋ ions. Based on the concentrations of Na^＋, K^＋, and Mg^2＋, evaporation was divided into three main precipitation stages as follows： halite dominant, carnallite dominant, and bischofite dominant. The δ^37Clsolid and δ^37Clliquid values of the precipitate and coexisting brine samples at different stages showed the following characteristics. The precipitates were enriched with δ^37Cl relative to the coexisting brine samples, and the δ^37Cl of both the precipitate and brine samples decreased gradually during evaporation. The fractionation factors （ah） between halite and brine were the highest, followed by that （ac） between carnallite and brine, and then that （ab） between bischofite and brine. The ac and ab values of less than one, which indicate the precipitate is enriched in 35^Cl, were found when the evaporation process entered a new stage. However, the δ^37Cl values of carnallite, bischofite, and the coexisting brine samples decreased during evaporation. The residual brine is a 35^Cl reservoir. The experimental phenomena were consistent with the δ^37Cl values in saline deposits in the literature. δ^37Cl can be used as an indicator of brine evaporation processes, which is important in the exploration of sylvinite deposits.

关 键 词：盐湖卤水 蒸发过程 氯同位素 同位素分馏 稳定 水氯镁石 卤水蒸发 实验过程 

分 类 号：P619.211[天文地球—矿床学]