Bracksh and fresh water distribute alternately in inland plains.At present,the cause of salt water and the hydrogeochemical during brackish water quality evolution are lack of awareness.Therefore,on the basis of the research of water chemical characteristics in inland plains and with the method of geological drilling,pumping test,water analysis,samples of clay are taken,the depth of which is from 42 m to 48.2 m.Samples of groundwater are taken in salt water distribution area,and are tested for chemical indicators.Then start isothermal adsorption experiment for Na +,Ca2+,Mg2+ in salt water and the clay.Results show that:①The clay adsorbing the conventional ion reaches adsorption equilibrium in groundwater within 3 h.The adsorption rate is a process that is from quickness to tardiness;②The maximum amount of the clay adsorbing Na +,Ca2+ and Mg2+ in the groumdwater are 1 302 mg/kg,733.1 mg/kg,528.49 mg/kg.The adsorption isotherms that the clay adsorbs the conventional ion are all fit for Langmuir equation.③The clay adsorbing and blocking Na + and Mg2 + are greater than Ca2 + in the groumdwater.Study shows that the clay has the certain control function in the belt of hydrochemistry type in shallow groundwater system and the formation of Na,Mg brackish water.%内陆平原区成淡水交替分布,目前对于咸水成因、咸淡水水质演化过程的水文地球化学作用缺乏认识.因此,在研究内陆平原区水化学特征基础上,采用地质钻探、抽水试验、水质分析等方法,采取研究区深度42～48.2 m的黏土样品和地下水水样,并测试水化学指标,对咸水中Na+、Ca2、Mg2+与黏土进行吸附等温实验.结果表明:①黏土吸附地下水中的常规离子能在3h内达到吸附平衡,吸附速率是一个由快到缓的变化过程;②黏土对地下水中Na+、Ca2、Mg2+的最大吸附量分别为1 302 mg/kg、733.1 mg/kg、528.49 mg/kg,等温吸附曲线较符合Langmuir方程;③黏土对地下水中Na+、Mg2+的吸附、阻滞作用大于对地下水中Ca2+的吸附、阻滞作用.研究表明,黏土对地下水系统中的水化学分带及浅层地下水系统中Na、Mg型微咸水的形成有一定控制作用.
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