Experimental Study On Resistivity Method In Leachate Migration Detection Of Phosphogypsum Yard

Phosphogypsum is a by-product of wet-process phosphoric acid process.Openair centralized storage is the main treatment method at this stage.In the long-term stacking process,the yard is leached and weathered,resulting in the precipitation of toxic substances,which seriously endangers the local ecological environment.In the context of strict national environmental protection policies,the detection and evaluation of contaminated sites has become a research hotspot.As an inherent property of soil,resistivity has significant differences before and after soil pollution.Although the direct current resistivity method has been applied in the field of environmental pollution investigation,there are few reports on the resistivity characteristics of phosphogypsum leachate and its influence on soil resistivity.In order to evaluate the application effect of resistivity method in the detection of leachate pollution in phosphogypsum yard,this paper takes Guizhou red clay as the research object.Firstly,the resistivity characteristics of phosphogypsum leachate and its contaminated soil are analyzed by physical property experiments,and the quantitative model of leachate content and red clay is established based on the improved Archie formula.Then,with the help of a commonly used resistivity methodhigh density resistivity method(ERT),the physical simulation experiments of leachate monitoring under different leakage modes were carried out to study the spatial distribution characteristics of resistivity of leachate in the process of surface and internal pipeline leakage,and the leakage process of karst water under the same experimental conditions was compared.Finally,through the sampling analysis around the yard and the measurement of high-density electrical method,the application effect of resistivity method in the leakage monitoring of phosphogypsum yard is verified.The main results are as follows :(1)The resistivity characteristics of different pollutants were discussed by symmetrical quadrupole resistivity experiment.The results showed that the resistivity method had the best detection effect when the leachate concentration was within 40 %.The effects of concentration,soil moisture content,porosity and saturation on the resistivity of contaminated soil were compared.The orthogonal experiment was used to analyze the influence of various factors on the resistivity of soil,and the order was leachate concentration > moisture content > porosity.The resistivity model of leachate contaminated soil was normalized based on the resistivity of uncontaminated soil.The three factors of leachate concentration,water content and porosity were introduced to construct the resistivity prediction model of contaminated soil.The correlation coefficient was 0.982,and the calculated value of the model was in good agreement with the measured value,which could be used for the preliminary evaluation of phosphogypsum leachate contaminated site in red clay area.(2)The infiltration process of phosphogypsum leachate under different leakage modes was measured in real time by physical simulation experiment.The results showed that the resistivity of leachate and its contaminated soil decreased with the increase of leachate concentration,and the change in low concentration range was more severe.In the process of surface single point infiltration,the leachate mainly migrates horizontally and gradually forms a funnel-shaped leakage pattern,while the leachate migrates in a peripheral diffusion mode under the pipeline leakage mode.After adding karst water,the polluted area and unpolluted area under the same water content can be distinguished by resistivity difference.(3)Two phosphogypsum yards in Guizhou were selected to carry out on-site high-density electrical experiments,and Xifeng yard was selected for sampling analysis.It is verified by examples that under complex conditions,the high-density electrical method has a more obvious reflection of the low-resistance anomaly caused by leachate,and can accurately reflect the location and depth information of the lowresistance anomaly body.By comparing the profile results of each survey line,the diffusion direction and pollution depth of leachate are roughly judged,and the pollution boundary is divided.The results of sampling chemical experiments further verify the conclusion of high density electrical method.The above experimental results provide a feasible basis for subsequent information such as degree and resistivity characteristics,which is conducive to later prevention and control.