Changes Of Salt Content And Ion Migration During Freezing And Thawing Of Salt Water In Southern Xinjiang

Xinjiang is located in an arid inland area,with little rainfall,more evaporation,and lack of fresh water resources,which seriously restricts the social and economic development of Xinjiang.The southern Xinjiang region has abundant salt water resource,but it has not been effectively utilized,causing serious pollution to the irrigation drainage carrier..Therefore,the development and utilization of saltwater in the southern Xinjiang is urgent.As an effective way to alleviate the shortage of freshwater resources and reduce water pollution,salt water desalination has attracted many scholars’attention.The freezing method has the advantages of low energy consumption,simple pretreatment,and light corrosion.It is an efficient salt water desalination technology,and has made in-depth research in desalination efficiency,economic effect,and energy loss.However,the variation law of salt and ions in freezing and thawing process is not clear.Therefore,this paper takes salt water（farmland drainage,groundwater）in southern Xinjiang as the research object,and explores different temperature treatments（-6,-12,-18°C）,different cold area treatments（20 cm×20cm,25 cm×25 cm,30 cm×30 cm）,different freezing methods（graded freezing,complete freezing）and different melting methods（conventional melting,gravity desalination）through indoor simulation experiments of freezing method..The main conclusions of the experiment are as follows:（1）During the freezing process of farmland drainage and groundwater grading freeze-thaw test,the salinity of the ice-melt water increased with the increase of the freezing stage,and increased significantly with the decrease of the freezing temperature（P<0.05）.The salt removal effect was the worst at-18℃.There is a good linear fitting relationship between the salinity of ice melt water and the salinity of concentrated water;the salinity threshold of concentrated water decreases with the decrease of freezing temperature,and the slope of the fitting line is-18℃>-12℃>-6℃distribution law.（2）During the freezing process of farmland drainage and groundwater classification freeze-thaw test,the ion concentration of ice-melt water increased with the increase of freezing stage,and the decrease of freezing temperature increased significantly（P<0.05）,and the ion removal effect was the best at-6℃.In the progressive freezing process of ice crystals,,when the freezing stage is the first stage,the freezing ratio of each ion follows the distribution law of SO₄^2->Na⁺>Cl^->K⁺,and the freezing ratio of SO₄^2-is higher than that of other ions under each temperature treatment.The migration rates of each ion into the ice crystal are different,and the slope of ion icing ratio fitting line is K⁺>Cl^->Na⁺>SO₄^2-.（3）During the ice melting process of farmland drainage and groundwater grading freeze-thaw test the salinity of ice-melt water decreased rapidly at first,then slowly,and finally tended to be stable.There is a good exponential decay relationship between the salinity and melting amount of ice-melt water..Under the same solution concentration,the melting amount threshold decreases with the increase of freezing temperature;under the same freezing temperature,the melting threshold increases with the increase of freezing stage.（4）During the ice thawing process of the farmland drainage and groundwater grading freeze-thaw test,the Cl^-,K⁺,Na⁺concentrations showed a trend of rapid decline at first,then a slow decline,and finally stabilized during the ice crystal thawing process;SO₄^2-concentration The downward trend is stable.（5）During the freezing process of the complete freeze-thaw test of farmland drainage,the salinity and ion concentration of the ice-melt water decreased with the increase of the freezing temperature,and increased with the increase of the thickness of the ice layer.Under-6℃treatment,the salt and ion content in the ice-melting water is the lowest,and the salt and ion removal effect is the best.（6）During the freezing process of the complete freeze-thaw test of farmland drainage,during the gradual melting of ice crystals,the salinity,Cl^-,K⁺,and Na⁺concentrations of the ice-melt water decreased rapidly at first,then decreased slowly,and finally stabilized.The decreasing trend of SO₄^2-concentration is stable.To sum up,in the staged freezing test,when the freezing temperature is-6°C,the freezing stage is the first stage during the ice crystal freezing process,and the ice melting stage is the fifth stage during the ice crystal melting process,melt water has the lowest salt and ion content.In the complete freezing test,when the freezing temperature is-6°C,the thickness of the ice layer is 3 cm,and the ice crystals are melted step by step,the salt and ion content in the ice melting water is the lowest when the ice melting stage is the fifth level.