Study On Remediation Of Colloidal Mg?OH?₂ Or Modified Bentonite On Multiple Heavy Metals Contaminated Soil

In recent years,a large number of abandoned mines have caused serious soil heavy metal pollution.Heavy metals are non-degradable and difficult to completely remove from the environment.They can enter the body of animals and plants with the biological chain,and endanger human health.Abandoned mine soils are all polluted by compound heavy metals,and will migrate with acid mine wastewater to pollute the surrounding soil.Remediation of compound heavy metal contaminated soil in abandoned mines is one of the hot issues that need to be solved urgently.Chemical stabilization technology is a simple,short-term,and effective method for remediation of heavy metal contaminated soil.The study of an effective,environmentally friendly,and inexpensive chemical stabilizer is the main content of the technology.Mg?OH?₂ can produce hydroxide precipitation with heavy metals,which can reduce the mobility and biotoxicity of heavy metals in the soil,and slowly release OH^-,so that the pH of the soil will not change sharply and damage the soil ecological environment.In this thesis,Mg?OH?₂ modified with sodium lauryl sulfate?SDS?and Tween 80 was used to prepare a colloidal material with Mg?OH?₂ particles coated with surfactant,colloidal Mg?OH?₂ The release rate of OH^-is lower than that of Mg?OH?₂,and the slow-release property is enhanced,which can improve the acid waste mine soil and maintain the soil pH.Due to the high pH required for the precipitation of cadmium,colloidal Mg?OH?₂ has a low stability to cadmium.This paper uses Mg?OH?₂ to modify bentonite,which has strong adsorption capacity,large ion exchange capacity,and Mg?OH?₂ Modification can enhance the ion exchange capacity of bentonite and improve its stabilizing effect on heavy metals.The experimental research in this paper includes two parts:First,the use of modified Mg?OH?₂ and modified bentonite to repair Pb,Cd,Cu,and Zn-contaminated soil,and the evaluation of the two stabilizers in terms of bioavailability and morphological distribution of heavy metals Remediation effect;Secondly,the soil after remediation of modified Mg?OH?₂ and modified bentonite using simulated column leaching was used to study the re-release of heavy metals in the soil after remediation,and the remediation effects of the two stabilizers were comprehensively compared.The main conclusions are as follows:?1?After adding modified Mg?OH?₂ to repair heavy metal contaminated soil,the stabilization efficiency for lead,cadmium,copper and zinc was 72.42%,34.53%,87.64%and 97.65%,respectively,and modified Mg?OH?₂ It can significantly reduce the heavy metal exchange state content and increase the residual state content.In addition,the modified Mg?OH?₂ has a slow release property,can release OH^-for a long time,maintain the soil pH to be weakly alkaline,and increase the stability of heavy metals in the soil with time.It is a cost-effective soil stabilizer for heavy metal pollution.?2?Mg?OH?₂ modified bentonite enables ion exchange between Mg²⁺and bentonite interlayer cations,which expands the interlayer structure and enhances ion exchange capacity.At the same time,increasing the surface OH^-content can form precipitation with heavy metal ions.The adsorption efficiency of heavy metals in the heavy metal coexistence system is higher than that of bentonite.Modified bentonite is used to repair heavy metal-contaminated soil.The stabilization efficiency for Pb,Cu,and Zn is about 100%,and the stabilization efficiency for Cd is 78.22%.The heavy metals in the soil after repair are mainly in the form of residues.?3?After the modified Mg?OH?₂ and modified bentonite were used to repair the soil after rainwater,acid rain and mining wastewater leaching,the heavy metals hardly dissolve,the form of heavy metals in the soil did not change,and there was no problem of heavy metal re-release.Acid rain and leaching of mine wastewater will slightly reduce the soil pH,but the pH value is still above 7.The pH of the modified Mg?OH?₂ repair soil decreases less than the modified bentonite repair soil,and the buffering capacity is stronger.?4?Modified Mg?OH?₂ and modified bentonite are both economically effective and environmentally friendly soil stabilizers,which reduce the mobility,toxicity and bioavailability of heavy metals in the soil.Modified Mg?OH?₂ repairs Pb and Cu in soil.Residual state content is more,while modified bentonite has higher stabilization efficiency and higher residual state content.The two kinds of stabilizers have similar repair effects on Zn in soil,and the stabilization efficiency is close to 100%.