Study Of The Effect Of Morphological Transformation Of Cadmium And Lead In Soils On Longitudinal Wave Velocity

The wide distribution and irreversible damage of heavy metals have driven the development of soil contamination identification techniques.Traditional techniques for contamination identification revolve around chemical composition analysis,which involves complex sampling and testing processes and may result in secondary contamination.Considering that geophysical exploration has been widely used in oil and gas exploration and fracture extension,the distribution and transformation characteristics of heavy metals in soil can be traced based on the principle of this technique.In this paper,the variation pattern of soil compression wave velocity under the influence of cadmium and lead concentration is studied and used to predict the concentration range of heavy metals in soil.Based on the variability of morphological distribution of heavy metals in the solid-liquid phase of soil and the mechanism of mutual transformation between morphologies under the influence of moisture,the effects of changes in the concentrations of cadmium and lead and water content on the propagation of compressional waves within the soil were investigated in depth.The main research results are as follows.(1)Soil compressional wave velocity increases firstly with the increase of cadmium and lead concentrations and then gradually stabilizes.This trend is related to the distribution of cadmium and lead in the solid-liquid phase of the soil,and the wave velocity value corresponding to the saturation of cadmium and lead adsorption is the largest.At the same time,due to the difference of soil sorption capacity for different types of metals,the concentration corresponding to the maximum value of wave velocity of lead-contaminated soil is significantly higher than that of cadmiumcontaminated soil at the maximum wave velocity.(2)Both cadmium and lead contaminated soil compressional wave velocity decreases with the increase of mass water content.This is mainly because the increase of water content leads to the enhancement of soil oxidation and acidity,and the carbonate bound state,iron-manganese oxide bound state and organic bound state of cadmium and lead gradually transform to ion exchangeable state,which in turn increases the total soil volume and porosity.(3)Constructing a model for predicting soil pollution concentration by compressional wave velocity.Apply the change law of soil compressional wave velocity under the influence of cadmium and lead pollution concentration and water content to the prediction of soil pollution range of unknown concentration,the results show that the minimum concentration interval of cadmium and lead predicted by the compressional wave velocity method can meet the accuracy of the actual pollution concentration.The study of the reasons for the variation of soil compressional wave velocity under cadmium and lead contamination can help to understand the influence of morphological transformation on compressional wave propagation,which is beneficial to the construction of the model for predicting contamination concentration by compressional wave velocity.This technique provides a theoretical basis for the prediction of the type of heavy metal contamination and the concentration range of the site by the wave velocity method.The in-situ,non-destructive identification of the extent of site contamination will then provide technical support for subsequent contamination assessment and remediation.