Distribution Characteristics And Enrichment Factors Of Fluoride In Groundwater In Typical Areas Of Southern Xinjiang

Fluoride is one of the necessary trace elements in the human body.Its chemical properties are active,and the ionic form is easily soluble in water and absorbed by the human body.It is an indispensable mineral of teeth and bones,but it is also a toxic element.Fluoride concentration is too high or too low will endanger human health and cause endemic diseases.Fluoride poisoning caused by high fluoride concentration was more harmful.In the northwest inland arid areas of China,especially in the Tarim Basin,Junggar Basin,Guanzhong Basin fluorosis phenomenon is the most serious.To study the distribution of groundwater fluoride in southern Xinjiang,Kashi Prefecture was selected as the typical areas.Based on the groundwater test data of typical areas,this paper analyzed the spatial distribution characteristics,enrichment factors and formation mechanism of groundwater fluoride in Kashi Prefecture.The main conclusions were as follows:?1?The spatial distribution characteristics of groundwater fluoride in the study area:horizontally,Fluoride concentration in groundwater had no obvious zoning in Kashgar River Basin.Fluoride concentration in groundwater gradually increased from the south to the north in Yarkant River basin.Vertical distribution of fluoride concentration in confined groundwater was that in Kashgar River Basin,deep confined groundwater>shallow confined groundwater;and of which in Yarkant River basin,shallow confined groundwater>deep confined groundwater.?2?Groundwater fluoride of the study area was mainly derived from fluoride minerals,fluoride-containing soils and fluoride in surface water.?3?The topography was the main external factors that affect the groundwater fluoride concentration in unconfined groundwater.The hydrogeological condition was the main external factors of confined groundwater fluoride enrichment.?4?High fluoride groundwater appeared within a specific pH range,and the weak alkaline groundwater environment had a certain effect on fluoride enrichment.Hydrochemistry environment of high TDS,TH,HCO₃^-and Na⁺can promoted fluoride enrichment.In the study area,the hydrochemistry type of high fluoride groundwater was not consistent with the previous study that the main hydrochemistry type of high fluoride groundwater was HCO₃ type,which was caused by the high TDS in groundwater of the study areas.?5?The saturation index and the activity relationship between F^-and Ca²⁺indicated that high fluoride groundwater was due to the dissolution of fluorite.The precipitation of dolomite and calcite decreased the Ca²⁺and Mg²⁺concentration and provided the conditions for fluoride enrichment.Gibbs diagram showed that the high fluoride groundwater in Kashgar Prefecture was mainly controlled by the dual effects of rock weathering and evaporation,and the evaporation effect was stronger than rock weathering.?6?PHREEQC software was used to calculate the transfer amount of minerals in unconfined groundwater,shallow confined groundwater and deep confined groundwate.Results showed that the increase of fluoride concentration in groundwater was mainly derived from the dissolution of fluorite minerals.