Migration Characteristic Of Heavy Metal Pb²⁺ In Sand

The problem of heavy metal pollution in the soil has become a concern of all countries in the world,and it has become one of the environmental problems that the world is now eager to solve.Lead is the main influencing factor of heavy metal pollution in the soil.How to reduce the content of heavy metals in the soil is the key to completely alleviate or even solve heavy metal pollution.The traditional solution is not only costly,but also can not get significant results.Therefore,researching and understanding of the migration and adsorption characteristics of heavy metal ion lead in sand can solve the problem of heavy metal lead pollution in essence.This subject firstly tested the basic physical properties of the sand using in the test through classical geotechnical tests;Then,EDS,SEM and XRD were used to study the changes of microscopic characterization of sand before and after adsorption of heavy metal ions,revealing the form of heavy metal ions adsorbed by sand;Furthermore,the static equilibrium adsorption test and the dynamic soil column simulation test were carried out.The special sand for sand filling method and silt sand were selected as the representative sand soil to study the migration and adsorption characteristics of heavy metal lead ions in sand;Through analysising,reveal the migration and adsorption characteristics of sand for heavy metal lead ions.（1）The microscopic characterization of sand by EDS,SEM and XRD can fully prove that the removal mechanism of Pb²⁺in solution is the adsorption of special sand for sand filling method and silt.（2）In the static equilibrium adsorption test of special sand for sand filling method,the static equilibrium adsorption data of heavy metal Pb²⁺accords with Langmuir model（R²=0.99）and D-R model（R²=0.905）,and the static adsorption capacity of standard sand for Pb²⁺is0.7mg/g.（3）This study investigated the effects of environmental factors such as initial concentration and flow rate on the migration of heavy metal ions.The results show:Increasing the initial concentration and flow rate of the influent will significantly reduce the initial penetration and complete penetration time of the sand column,otherwise,the larger the initial concentration and the larger the flow rate,the shorter the penetration time.Taking C₀=35mg/L as an example,when Q=10ml/min,the penetration time is 13000min,and when the flow rate is increased to60ml/min,the penetration time is only 2000min,and the duration is shortened by nearly 85%.（4）In the dynamic soil column test of special sand for sand filling method,the dynamic penetration test data of heavy metal Pb²⁺is in accordance with Thomas model（R²>0.93）,the measured value is close to the predicted value of the model,and the dynamic adsorption capacity value is between 0.5-0.75mg/g,but in terms of overall adsorption capacity is much lower than other fine-grained soil.（5）The dynamic soil column test was carried out under the condition of changing the particle grading.It was found that the dynamic penetration test data of heavy metal Pb²⁺accords with the Thomas model（R²>0.95）,and the measured value is close to the predicted value of the model.When the special sand and silt are mixed according to 2:1,the main distribution range of the dynamic adsorption capacity Q_calal of the soil column is between 1.0 and 1.85.When the special sand and silt are mixed according to 1:2,the main distribution range of the dynamic adsorption capacity Q_calal of the soil column is between 8.1-9.9.Through the whole test process,the migration and adsorption characteristics of heavy metal ion lead in sand can be described more accurately.getting this rule can help us understand the pollution mechanism of heavy metals on sand,prevent the pollution of heavy metals on sand in advance,and effectively alleviate the pollution of heavy metals on sand,and provide a new idea for the prevention and control of heavy metal pollution.Based on the further analysis of the data obtained from the test,it has certain reference and guidance value for the repair and prevention of heavy metal contaminated sites.