Study On The Purification Of Heavy Metal Pollution In Soil By EDTA Functional Magnetic Mesoporous Nano Materials

Remediation of heavy metal pollution in low permeability cohesive soil is the key and difficult problem of soil pollution remediation.At present,the main method for remediation of soil heavy metal pollution is solidification and stabilization,but heavy metals still remain in the soil and the pollution risk has not been removed.Different from this,this paper aims to explore a green,efficient and thorough method to purify soil heavy metal pollution.In this paper,a functional magnetic mesoporous nanomaterial is designed and prepared,which has the advantages of heavy metal philophile and clay phobic particles and is easy to be separated and extracted by magnetic force.In this experiment,magnetic nanomaterial adsorbent was added to saturated cadmium-polluted soil.After adsorption equilibrium,magnetic stirring was used to separate and extract magnetic nanomaterials and heavy metals.The soil was purified and the following results were obtained:?1?Magnetic core Fe₃O₄was prepared by coprecipitation method,and the average particle size was 10-15nm.The magnetic mesoporous nanoparticles Fe₃O₄@Si O₂with uniform particle size and good dispersion were prepared by Stober method.The specific surface area before calcination was 305.8m²/g,the pore diameter was 2.5nm,and the average particle size after calcination was about 200nm.Then EDTA-Fe₃O₄@Si O₂was obtained by modification of sodium ethylenediamine triacetate with N-?trimethoxy silica propyl?.Ftir spectra showed that EDTA was successfully modified with a specific surface area of 803.5m²/g and a pore diameter of2.5nm.All the three kinds of magnetic nanoparticles have paramagnetic properties.?2?The optimal adsorption conditions of Fe₃O₄,Fe₃O₄@Si O₂and EDTA-Fe₃O₄@Si O₂on soil cadmium were explored through laboratory simulation experiments.The adsorption effect of magnetic nanomaterial adsorbent modified with EDTA was significantly improved.The optimal experimental conditions were determined as follows:the temperature was 25?,the initial p H value was 7,the adsorption time was selected for 48h,and the adsorbent dosage was 20mg when the initial concentration of 10g cadmium contaminated soil was 10mg/Kg.Based on the analysis of thermodynamics,adsorption isotherm and adsorption kinetics,it can be speculated that the reaction is a dynamic process,and the adsorption mechanism includes spontaneous exothermic adsorption processes dominated by chemical adsorption such as physical adsorption and ion exchange adsorption.EDTA-Fe₃O₄@Si O₂adsorbent can be recycled.?3?The experimental results of remediation of soil Cd???pollution under the optimal adsorption conditions showed that the removal rate of Cd???by the adsorbent EDTA-Fe₃O₄@Si O₂reached 68.12%when the reaction was up to 48h.After the analysis of soil morphology before and after purification,the proportions of various morphology,ferric and manganese oxide cadmium and residue cadmium gradually decreased,the proportions of carbonate binding cadmium,organic cadmium and exchangeable cadmium indeed increased.The removal rates were in turn carbonate binding cadmium>residue cadmium>iron manganese oxide binding cadmium>exchangeable cadmium>organic binding cadmium.The amount of magnetic EDTA-Fe₃O₄@Si O₂nanomaterials recovered was 71.23%,and the amount of soil taken out was 5.613g,accounting for 2.8%of the total amount of remediation soil.The adsorption mechanism of adsorbent on heavy metal Cd???in soil is relatively complex and varied,and the comparative analysis shows that the experimental mechanism includes ion exchange,complexation and electrostatic adsorption on particle surface.