Groundwater And Sediment Characteristics Of Kuitun River Basin And Its Influence On Arsenic In Aquifer

Arsenic is a toxic metalloid element.The endemic arsenic poisoning of high arsenic groundwater has become one of the most difficult problems facing the international community in environmental geology.Although Kuitun River Basin is the first endemic arsenism area in China,compared with Songnen Plain and Datong Basin,the geochemical research on high arsenic groundwater in this area is still not deep enough.Relationship between particle size distribution of aquifer sediments and arsenic content in aquifer is not well understood.In this study,the high arsenic groundwater in Kuitun River Basin was taken as the research object.By combining field investigation with laboratory experiment,physical analysis,chemical analysis and mathematical statistical analysis,the influence of groundwater and sediment characteristics in Kuitun River Basin on arsenic in aquifer was discussed,which provided a scientific theoretical basis for the development and utilization of groundwater,the prevention and treatment of endemic arsenic water poisoning.The main conclusions of this study are as follows:(1)The p H value of high arsenic groundwater in Kuitun River basin is 7.7?9.0,and the Eh of high arsenic groundwater is-216?-3 m V,which indicates that alkalescence,alkaline water and reducing environment are beneficial to the formation of high arsenic groundwater in the study area.Hydrochemical types are mainly SO₄·HCO₃-Na and Cl·HCO₃-Na.According to Gibbs diagram analysis,evaporation concentration and rock weathering in this study area both control the ion composition of groundwater.(2)The As content of sediments in the study area is 8.36?28.41 mg·kg^-1.As content in clay layer is higher than that in sand layer,which indicates that the As content in sediments is closely related to lithology.Sediments with different grain sizes play different roles in arsenic migration and transformation.When the grain size is less than 16m,there is a significant positive correlation(the strongest correlation)between sediment As content and grain proportion,followed by 16<?<20?m;between 20<?<63?m,63<?<200?m and?>200?m,there is a negative correlation between sediment As content and grain proportion.The negative correlation keeps increasing,which indicates that the content of As in sediments is closely related to the particle size,and the smaller the particles in sediments,the more arsenic is enriched.The hydraulic conductivity coefficient of C1 and C2 borehole sediments is negatively correlated with As content in sediments,which indicates that the hydrodynamic conditions of groundwater have great influence on arsenic enrichment.Aquifer sediments with smaller hydraulic conductivity coefficient has more As content.(3)The migration of As in groundwater is not only affected by the reduction and dissolution of Fe and Mn hydroxides,but also controlled by the competitive adsorption of PO₄^3-and HCO₃^-.The oxidation environment indicated by high concentrations of NO₃^-and SO₄^2-can restrict the release of As to a certain extent.As(?)is the main existing form of As in groundwater.A large amount of As(?)will reduce the spatial migration ability of arsenic in groundwater.From the hydrogen and oxygen isotope and Gibbs diagram of groundwater in the study area,it can be seen that strong evaporation has a significant impact on the concentration and enrichment of arsenic in groundwater.(4)There is a positive correlation between arsenic content in sediment and in groundwater at corresponding depth,which indicates that As content in sediment is a factor affecting As concentration in groundwater.There is usually a significant positive correlation between As and Fe,Mn content in sediments,which indicates that arsenic tends to be enriched in sediments with high Fe,Mn content,while in a strong reduction environment,there is a negative correlation between As and Fe,Mn content due to adsorption of analytical arsenic by iron hydroxide or competitive adsorption between As and other anions(such as phosphate and bicarbonate)on the surface of iron and manganese oxides.