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A Study On The Binding Mechanism Of W(Ⅵ) On Soil Typical Components

Posted on:2023-06-05Degree:MasterType:Thesis
Country:ChinaCandidate:X LiuFull Text:PDF
GTID:2531307142974929Subject:Environmental Science and Engineering
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Tungsten has been listed as an emerging contaminant by the United States Environmental Protection Agency(EPA),which usually exists in the form of tungstate(WO42–)with high mobility.It can accumulate in the soil through various pathways,and further causing potential harm to the soil environment.The adsorption behavior of tungsten in soil determines its bioavailability and fate,but our understanding of this basic process is still lacking.Three typical soil components were selected in this study:minerals(kaolinite,montmorillonite and goethite),microorganisms(bacteria)and organic matter(humic acid,fulvic acid and soil DOM),through a series of macroscopic adsorption experiments,with the help of modern instrument analysis methods,including in-situ infrared spectroscopy(ATR-FTIR),X-ray photoelectron spectroscopy(XPS),ultraviolet-visible spectroscopy(UV-Vis)and three-dimensional fluorescence spectroscopy(3DEEM),to explore the binding mechanism of tungsten on various soil components.The main results are as follows:(1)In the minerals system,the highest adsorption capacity of the three minerals follows:goethite(58 mg·g-1)>kaolinite(17.5 mg·g-1)>montmorillonite(13.9 mg·g-1).The adsorbed W(VI)are in three forms,one is to form an external complex in the form of tungstate by electrostatic action,the other is to form an internal complex(Al/Si/Fe-O-W)on the surface of minerals,and the third is that polymerized tungsten on goethite under acidic conditions.In addition,the adsorption of W(VI)on three minerals was affected by p H,cation or anion,and humic acid.The adsorption capacity decreased with the increase of p H,increased with the increase of Na+concentration,and decreased with the increase of PO43-or humic acid concentration.(2)In the microorganisms system,the theoretical maximum adsorption capacity of the gram-negative bacteria Delftia sp.and gram-positive bacteria Bacillus cereus to W(VI)was89.97 mg·g–1 and 88.05 mg·g–1,respectively,at p H 3.5.Bacteria adsorbed W(VI)mainly through carboxyl groups(-COOH),which may form a stable C=O-O-W complex.In addition,the adsorption of W(VI)on the two bacteria was affected by p H and different cell states.The adsorption capacity decreased with the increase of p H,and the inactivated bacteria was slightly higher than that of non-inactivated bacteria.(3)In the organic matter system,the organic matter mainly formed stable complexes with W(VI)through substituted phenols,carboxyl groups and phenolic hydroxyl groups,and HA and FA have a certain reducing ability(HA>FA),which reduced W(VI)to a more stable W(V).In addition,the adsorption of W(VI)on the three organic matters was affected by p H,initial concentration of tungsten and cation or anion.With the increase of p H and initial concentration of tungsten,the complexing degree of humic acid,fulvic acid and soil DOM with tungsten decreased.Ca2+promoted the adsorption of W(VI)by organic matter,while PO43-inhibited this adsorption.
Keywords/Search Tags:Tungsten, Silicate clay minerals, Iron oxide, Bacteria, Organic matter, Adsorption, Complexation mechanism
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