The Research On Removal Of Heavy Metals Contaminated Soil At WEEE-Recycling Sites By Bioleaching

The electronic product replacement is fast,and the amount is large.Due to the irregular dismantling,it causes serious heavy metal pollution to the soil,posing a great threat to human health.Acidithiobacillus ferrooxidans?A.f?has strong tolerance to heavy metals and can change the form of heavy metals in soil and reduce the content.In this paper,the typical electronic wastes are investigated and sampled to determine the content and distribution of heavy metals in the soil.At the same time,the tolerance and removal ability of A.f bacteria to heavy metals are investigated.Then the main factors affecting the leaching of heavy metals in soil by microorganisms are discussed.Comparing the changes of the morphology and content of heavy metals under different conditions.The response surface-Box-Behnken design experiment was carried out on the basis of single factor.Finally,the physical and chemical properties of the leached soil were measured by the changes of soil physical and chemical properties before and after microbial leaching.Nature is restored.The main results are as follows:The site of the typical electronic waste dismantling area in Wenling,Zhejiang Province was selected for investigation and sampling,and the heavy metal content and morphology of the collected soil were analyzed and determined.It was found that the soil in the study area has been seriously polluted by heavy metals?Cd,Cu,Zn and Ni?.Among them,Cd,Cu,and Zn are heavily polluted,exceeding the standard number by more than 10 times,and most of them are in exchangeable state in the soil,which is highly toxic.A.f bacteria were domesticated with heavy metal contaminated soil as a material to improve their heavy metal tolerance and removal capacity.It was found that the heavy metal tolerance and removal ability of A.f bacteria were significantly improved after domestication.The effects of solid-liquid ratio,inoculum size,initial pH and FeSO₄·7H₂O content on heavy metal content and morphological changes in microbial leaching soil were investigated.Based on the single factor experiment,according to the Box-Behnke central combination experimental design principle,solids were selected.The liquid ratio?X₁?,inoculum?X₂?,initial pH?X₃?and FeSO₄·7H₂O content?X₄?were used as independent variables,and the heavy metal removal rate?Y_i?was used as the response value to design the 4 factor 3 level response.Surface test,the best process conditions were obtained through optimization experiments,and its application in engineering was simulated.Through the comprehensive test of response surface,the optimum removal conditions of heavy metals Zn,Cd,Ni and Cu:solid-liquid ratio 1.2%,inoculum size 1.0%,initial pH 1.0,FeSO₄·7H₂O content 4.3%,heavy metal under this condition Zn,Cd,Ni and Cu were all obviously removedand the soil stability was improved;the solid-liquid ratio of bioleaching in industrial applications should be controlled at 5-10%.According to the changes of soil physical and chemical properties before and after leaching,the physical and chemical properties of the leached soil were restored by biochar and organic fertilizer.It was found that biochar could improve the pH of acid soil,and the leached soil was applied with organic fertilizer.After that,the contents of organic matter and total N,total P and total K were significantly improved.In summary,the soil of dismantling electronic waste is seriously polluted by heavy metals.Microbial leaching can effectively remove heavy metals from the soil and change the form of heavy metals in the soil,reducing the toxicity of heavy metals and improving soil stability.The leached soil nutrients can also be effectively improved to achieve the true repair of contaminated soil.