Simulation Study On Groundwater Dynamics Control Of Leaching Range Of In-situ Uranium Well Field

Uranium is an important national strategic resource.With the innovation of technology,the application field is becoming more and more extensive.At present,there are different methods for mining uranium.Among them,the in-situ leaching production process has become the main uranium mining technology in China due to its short construction period,low production cost,high resource utilization rate and good safety.Although compared with conventional uranium mining,in-situ leaching uranium has less environmental pollution,but because its production process is to inject leaching agent into the ore-bearing layer through liquid injection drilling,there is also existence the problem of environmental protection,Among them,the control of in-situ leaching range is the most important factor affecting the groundwater environment.Based on the survey of hydrogeological data of a sandstone uranium mine in Inner Mongolia,combined with the data collected by the survey,this study uses the groundwater numerical simulation software Visual Modflow.Compared with the previous studies only focusing on individual pumping units,based on the macroscopic analysis of the groundwater dynamics of the entire wellsite,the author studied the groundwater flow velocity field through microscopic simulation of groundwater dynamics,According to the characteristics of groundwater flow velocity field in the injection hole at the edge of the well pad,the determination method and influence mechanism of the leaching range are discussed.the research results are as follows:(1)A dynamic model for groundwater production in the study area was established,and a simulation calculation method for the groundwater flow rate field was added to the visual modflow groundwater dynamics simulation platform.The simulation calculation results are highly reliable and suitable for regional groundwater dynamic analysis.(2)Under the combined action of the hydrodynamics of natural groundwater flow field,pumping hole and injection hole,a depression is formed on the profile of the pumping hole in the in-situ leaching well site with the pumping hole as the center drawdown line,and the groundwater around the well site flows into the well site;in the profile of the injection hole,the water level rises higher at the injection hole,and most of the solvent flows back into the well due to the influence of the adjacent pumping hole In the field,a small part of the solvent at the edge of the injection hole is transported out of the well pad in the form of seepage dispersion or molecular diffusion.(3)Between the injection hole and the injection hole in the well site,and between the pumping hole and the pumping hole,the water level drop changes are in the shape of "U" and inverted "U",respectively.The location of the adjacent liquid extraction and injection holes has a decisive influence on the dynamic change of water level in the adjacent hole profile and injection profile.(4)The flow velocity of groundwater decreases exponentially with the increase of distance from the injection hole at the edge of the well pad.When the flow velocity of groundwater outside the well pad is about 3m away from the injection hole and about 4.5m from the extraction hole,the flow velocity drops abruptly,that is to say,the further away from the injection hole,the slower the flow velocity is,and the further away from the extraction hole,the slower the flow velocity into the well pad;according to the groundwater flow velocity field,the further delineation of the well pad's solution range can be made.(5)Due to the effect of pumping and natural groundwater flow,the migration distance of the leachate is significantly different in space.The migration distance of the leachate at the edge of the injection hole is greater than that of the top angle drill hole,parallel to the downstream area of groundwater flow,slightly greater than that in the upstream area,and the east and west of the well site perpendicular to the groundwater flow direction are approximately the same.It shows that the injection volume of a single hole has a decisive influence on the migration distance of the leachate,followed by the effect of the natural groundwater flow on the well site.(6)Under the condition that the distance between the injection hole and the pumping hole is determined,through the simulation calculation,the design of the well pad of the mine shows that the farthest distance that the solution can move within the mining life is about 60 m outside the edge injection hole,which is more in line with the leaching benefit and environmental protection requirements of the mine.The simulation and prediction conclusions can provide theoretical and technical support for the production and design of the in-situ leaching mine,which is conducive to saving production investment and construction costs,and protecting the ecological environment.