| Groundwater is a very important natural resources,as the development of industry and agriculture,groundwater has becoming the most important water-supply source in many cities.In recent years,with the exploitation of mineral resources and the unconscionable using of the resources,which cause a series of geology and groundwater pollution problems that intensifies water resources crisis.Groundwater ammonia nitrogen pollution led to water rich nutrition has become a hot issue in a remediation of groundwater pollution.The area of southern Jiangxi Province is one of the most rare earth reserves in our country,mining process develops form the original pool leaching and dump leaching to in-situ leaching process now,which makes the rate of rare earth mining comprehensive recovery increasing and the ecological pollution decreasing obviously.Due to using the ammonia sulfate as liquid injection in mining process, the leaching of ammonia nitrogen can cause the groundwater nitrogen pollution problem.According to the hydrology and geological conditions,geological features and terrain characteristics of the test ore block in southern Jiangxi province,the study can be generalized as two-dimensional unconfined heterogeneous of unsteady groundwater flow system.The paper dissects the study region by the FEFLOW software.According to the pumping and water pressure test get the permeability coefficient of aquifer,which can know the reasonable hydrology parameters zoning and simulates calculation of groundwater flow field.By compared with the actual flow achieves the purpose of identification authentication.Based on the generalization of groundwater flow system, it is divided into normal exploitation without measures, leaching measures and leaching + hydraulic capture to take prediction of ammonia transport modeling. The prediction results show that in terms of excessive ammonia area of groundwater, it were reduced by 6.3% and 90% in excessive area according to leaching measures and leaching + hydraulic capture measures, compared to normal measures, which the hydraulic capture effect is evident; and it were reduced by 74% and 78% as well in terms of peak concentration of ammonia nitrogen in groundwater, having a evident leaching result; and yet the age of ammonia restore in groundwater reduced 1.5 years than normal situation. According to the duration curve of concentration changes from 8 observation points, the ammonia concentration were first increased and then rapidly decays exponentially and in turn significantly reduced downstream from ore block edge to downstream; After setting hydraulic capture line in ore block edge, the downstream groundwater ammonia concentration outside of the line significantly reduced and compliance, which therefore explains that hydraulic capture can effectively prevent the high concentrationof ammonia from moving outside.The in-situ leaching process, although almost has no damage to the surface, and does not produce any waste, early liquid collection system of witch was imperfect, and the mother liquor collection rate was not high without taking comprehensive liquid collection system, resulting in higher ammonia nitrogen in groundwater. According to the characteristics of in-situ leaching technology and pollution pathways of groundwater, the groundwater pollution prevention and control measures should be in the light of the principle of combining with source control, zoning prevention and cure, pollution monitoring and emergency response. Taking the groundwater environmental protection measures can make the in-situ leaching index increased, and mother liquor recovery rate reaches more than 90%, thus effectively reducing the pollution to groundwater. |
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