The Formation Of Iron Minerals In The Extracellular Polymer Solution Of Iron Bacteria And Their Removal Of As(V) And P(V)

The polysaccharides and proteins in bacterial EPS contain a large number of organic active functional groups,which can be combined with iron to stabilize and deposit iron by oxidation or precipitation to form iron minerals.EPS plays a key role in the nucleation,growth and structural assembly of minerals.Iron minerals formed in the associated media of A.ferrooxidans bacteria such as cultures and EPS solutions are mainly sulfate-containing schwertmannite and jarosite.Their formation and phase transformation are not only related to bacterial cells and their secretion,but also affected by ambient conditions such as pH,anion Cl-/SO42-,cation K+/Na+/NH4+,and As(V)/P(V)contaminants.Therefore,in this dissertation,considering the above-mentioned influencing factors,a variety of characterization methods were used to conduct research on the formation of iron minerals and the removal of contamination ions in bacterial culture media and EPS solutions.The main results are as follows:The addition of iron salt and SO42-promotes the formation of jarosite and the aggregation of product particles,while the addition of Cl-can slow the aggregation of product particles.Under different Cl-/SI42--molar ratios,the main precipitated product formed in the EPS reaction solution containing sodium and ammonium salts was jarosite,and its product morphology was different.At the initial pH of 1.2-2.3,2.5,and 2.8,the iron minerals formed in the EPS solutions were jarosite and schwertmannite,jarosite and goethite,and goethite(spherical granules).In the As(?)-containing EPS reaction solution,the iron minerals are jarosite and schwertmannite,and the high concentration of As(V)will hinder the conversion of the initial mineral phase schwertite to jarosite.Removal of As(V)in the EPS reaction solution is related to the formation of iron mineral phase and product particle morphology,and the removal rate of As(V)is 42-22%.In a bacterial media with the appropriate concentrations of As(V),Fe2+initially forms Fe(OH)2 iron precipitates,then Fe2+ is biooxidized to Fe3+,and Fe3+ forms a mixture of iron minerals of jarosite(dispersed rock)and six-line ferrihydrite(globule)particles.The biooxidation of Fe2+ in medium containing high concentration of As(?)is inhibited,and the iron precipitation is mainly six-line ferrihydrite.As(?)is favorable for ferrihydrite formation in bacterial culture media.The arsenate is easily replaced by the sulfate ion in the jarosite structure,and the removal rate of As(?)is 45-57%.Ferric ion in the P(?)-containing EPS reaction solution forms jarosite(diamond-like or crescent-shaped block),and the P(?)removal rate is 27-12%.In a culture medium containing P(? at an appropriate concentratiol,Fe2+ initially forms Fe(OH)2 iron precipitates,and then Fe2+ is biooxidized to Fe3+,and Fe3+ forms iron precipitates containing yellow iron oxide and/or iron phosphate.Phosphate at high concentrations will inhibit the biological oxidation of Fe2+.Phosphate can hinder the formation of jarosite and promote the formation of iron phosphate.The removal rate of P(?)is 72-33%.The above results have potential significance for removing soluble Fe and SO42-in acidic mine wastewater and effectively controlling the formation of secondary minerals.It is favorable for revealing the mechanism of adsorption and passivation of toxic elements by iron minerals.It can be used in the environmental governance of special acidic water,and provides a theoretical basis.