Characteristics Of Groundwater Environment And Heavy Metals Transport In A Typical Metal Mine In Tongling,Anhui Province

The solid waste,waste water and the heavy metals released during the mining and production of large scale metal mines pose a threat to the surrounding ecological environment and the residents'health.Tongling is a typical ore concentration area in the ore belt of the middle and lower reaches of the Yangtze River,and also an important non-ferrous metal production base in China.Therefore,the impact of the development of the Tongling metal mine on the ecological environment is a typical regional representation.At present,the research on the environment of Tongling ore concentration area mainly concentrates on heavy metals pollution in the tailings pond,surface water bodies and soil.This study focuses on the groundwater in the concentration area.The Xinqiao-Shizishan mining area was taken as the research object,using wild field investigation,soil and water samples testing,combined with hydrochemistry analysis,isotope analysis,groundwater quality assessment,heavy metal pollution index,Self-Organizing Features Map(SOFM)neural network modeling and speciation analysis of heavy metals to explore the groundwater environment characteristics and the distribution and transport of heavy metals in groundwater.The following understandings have been obtained.1.The groundwater in the study area are mainly recharged by atmospheric precipitation and groundwater from mountain areas.The plain area is the main runoff and discharge area of groundwater.The hydrochemistry of the groundwater is determined by the discharge of acid mine water and the water-rock interaction of groundwater during runoff.The chemical characteristics of groundwater in the plain area are also affected by evaporation concentration,surface water recharge and runoff velocity.There is a distinct zonation of hydrochemical characteristics in the groundwater of this study area.The groundwater in mountainous areas is mainly SO₄-Ca type water with high TDS and low p H.The groundwater in runoff areas is mainly HCO₃-Ca type water with reduced TDS and increased p H.The groundwater in discharge areas has more complicated type with the TDS and SO₄^2-increased.2.The distribution of heavy metal elements is similar to that of TDS.In the mountainous area,the contents of heavy metals in groundwater are relatively high,which in the runoff area are relatively low,and in the discharge area are slightly increased.The heavy metal content of the groundwater is mainly affected by mining activities,industrial production,oxidation conditions and p H of the mining area.According to Class III water standard in groundwater quality standards,the EWQI(Entropy Water Quality Index)limit value of the regional groundwater is 100,and the HPI(Heavy mental Pollution Index)limit value is 8.0.The quality of groundwater in the area is generally good,and the excess components of individual water samples are SO₄^2-,NO₃^-,Mn,and Ni.3.The SOFM model can be used to comprehensively evaluate the major components and heavy metal components with great differences in groundwater of this study area.The optimal cluster number of groundwater samples calculated by SOFM in this area is five.These five types of groundwater are distributed along the groundwater runoff direction in the area,which represents the groundwater environment characteristics with different hydrogeological and hydrochemical characteristics in the study area.Groundwater of the area in summer is slightly better than in winter,and seasonal changes will also have an impact on the groundwater environment.4.The types and distribution of heavy metals in tailings reservoir,groundwater and soil are similar to those in the research area,the tailings reservoir is the main source of heavy metals,and the acidic mine water is formed by the high content of sulfur element oxidation to promote the release of heavy metals.However,the heavy metals speciation in the tailings reservoir is mainly residual state with low mobility.At the same time,lots of Fe and Mn in the zone become high valence state sediments after they enter the groundwater with higher oxidation and p H,and adsorb the heavy metal elements to form coprecipitation.The above reasons lead to a low content and poor mobility of heavy metals in groundwater,and enrichment in the soil.