Precipitation Mechanism Of Pb From Farmland Soil Around Ion-type Rare Earth Mines

In the investigation of rare earth minerals in Gannan area of Jiangxi Province,it is found that there is serious heavy metal lead pollution in the farmland around the Longnan rare earth mining area.This paper then studies the migration and transformation of lead ions in farmland soil around the Longnan area.In this experiment,the contaminated farmland soil around the rare earth mining area was taken as the research object,and the target pollutant was heavy metal lead.The study selected the passivating agent to be added to the farmland soil,and analyzed the change of the amount of lead passivation added by different passivating agents.In addition,simulating changes in heavy metal lead leaching and migration and transformation under natural leaching conditions according to the rainfall situation.It is mainly studied from three aspects: rainfall intensity,simulated rainfall pH and rainfall duration.Excessive amounts of ammonium sulphate solution are present in the soil surrounding the mining area mined by in-situ leaching.In this experiment,1.00~3.00% ammonium sulfate solution was added and observed the effect on heavy metal lead in farmland soil.Combined with the experimental results,use the response surface method to fit the experimental data and analyze the significance of the influencing factors.(1)In order to stabilize the heavy metal lead in contaminated farmland soil,the study tried to add passivating agent(attapulgite)to the experimental soil.After the use of passivating agent,the amount of heavy metal lead eluted under natural rainfall conditions has a tendency to decrease significantly.The results show that the passivator selected in the experiment will have a passivation stabilizing effect on the heavy metal lead in the farmland soil in the region,and the lead ions which are easy to be separated by the rain will be converted into a stable state which is not easy to leaching out.Thereby reducing the pollution of lead ions in the soil to farmland crops and surrounding surface runoff.When the addition amount of attapulgite was 10.00%,the stability of heavy metal lead was remarkable,and the lead content measured on the second day of the experiment decreased to 0.00 mg/kg.When the amount of attapulgite added was 2.00%,the measured lead content was 0.00 mg/kg when the experiment was carried out until the 8th day.(2)The study used simulated acid rain leaching experiments to observe the change ofleaching amount of heavy metal lead.The results show that the effect of duration on lead leaching has two phases: rapid decline and slow decline.The experimental conditions were designed by response surface methodology.The pH of the acid rain leaching filtrate was4.50~5.50,the rainfall intensity was 109.00~374.00mm/d,and the exogenous heavy metal lead was added 100.00~500.00mg/kg.Observing the amount of lead leaching in this case,it was found that with the decrease of pH value,the increase of leaching intensity caused the amount of lead leaching to rise first and then decrease.When the concentration of exogenous lead is gradually increased,the pH value of simulated acid rain and the increase of leaching intensity will increase the amount of lead elution.(3)The uncertainty of the amount of ammonium sulfate solution added during the mining of rare earth minerals makes the farmland soil around the mining area face the threat of being saturated with ammonium sulfate.According to the previous investigation results,it is concluded that the ammonium sulfate in heavy metal contaminated soil will be passivated.Combined with the actual situation of the mining area,different concentrations of ammonium sulfate solution were used in the leaching experiment of the experimental soil,the precipitation of heavy metal lead added to the farmland soil with lower concentration of ammonium sulfate was less than that of the high concentration ammonium sulfate.