Formation Of Iron Oxyhydroxides With Pore Structrue Under Regulation Of EPS Produced By Acidithiobacillus Ferrooxidans

Acidithiobacillus ferrooxidans(A. ferrooxidans), an acidophilic chemolithoautotroph, can use ferrous iron, reduced sulfur species, or metal sulfides as energy sources. Bacterial metabolization plays an important role in biological mineralization progress. In the biological mineralization system, both framed protein as template and function potein as regulator are excreted and synthesized by the corresponding cells. Also, bacterial activities can vitally impact the classification structures of mineralized organs. Oganic substances paly key role in the cases such as molecular recognization in the organic and inorganic interfaces, crystal nucleation and growth, microstructure assembling. Thereby, the organic substances of polysaccharide and potein excreted by microbial cells have been generally testified to be the significantly "active reagents" for biological minerals.A. ferrooxidans easily make a respose to the ingredients such as inorganic ions, organic compounds and heavy metals present in the bacterial media. For example, it is documented that sulfate is the necessary ion to the bacterial growth, while chloride ion has a restriction in the bacterial growth and biooxidation capacity. In our research work, it is proved that the bacterium of A. ferrooxidans can oxidize completely Fe2+ into Fe3+ and its cellular densities may reach the maximum in the media including 0.2 M of chloride. However, there is little valube information on the relationship of formation of iron minerals and rich in-EPS (Extracellular Ploymeric Substances) culture excluding the cells and the precipitates. It is worth carrying out in the relative works.Therefore, in the present works, we studied the medium compositions of A. ferrooxidans (which is isolated from the municipal sewage sludges) at stationary phase and the biological mineralization formation of iron oxyhydroxides under the regulation of extracellular polymeric substances, under the different conditions such as the different reaction temperatures, the Fe(II)/Fe(III) salts with various molar proportion of Cl/SO4. Moreover, we researched the biological mineralization formation of iron oxyhydroxides under the regulation of the various kinds of polysaccharide (glucose, trehalose, rhamnose, dextran, some of which is examined to occure in the bacterial EPS soultions) with different concentrations formed from the FeCl3 at various levels. The results of the studies are as follows:Using anthrone colorimetric measurement method for polysaccharide and Coomassie brilliant blue method for protein, the results showed polysaccharide content was the main componet with 87% and 13.5 times of the protein content. The extracellular polysaccharide substance extracted from culture media of A. ferrooxidans cells were further purified, so only extracellular polysaccharides were reserved. Glucose, arabinose and trehalose are the main compositions of the extracellular polysaccharide analyzed by gas chromatography and mass spectrometry (GC-MS).Results of the formation of iron minerals in EPS reaction solutions under 25℃-80℃ displayed the precipitate procucts are the mixed mineral phases of the main jarosite and some schwertmannite. Another mineral phase of goethite was observed in the product in solution with a reaction temperature of 80℃. In the systems with different molar proportion of Cl/SO4 under 40℃, the added Cl as FeCl3 have a restriction in formation of jarosite from schwertmannite as initial phase present in the EPS reaction solution. Moreover, reseach results for the reactions in addition of exterior Fe(Ⅱ)/Fe(Ⅲ) salts with Cl/SO4 (equal to 1,3,6 and 10) showed EPS can promote the precipitation of ferric ion and the oxidation of ferrous ion. Jarosite with particle morphology of "lozenge" as the main mineral phase are examined and testified occurrence in all precipitate products.Due to the sulfat initially present in EPS reaction solutions limiting the other phase of akaganeite resembling schwertmannite in the structure, the formation of iron oxyhydrooxides in FeCl3 solutions under the action of polysaccharides selected according to the identification result of EPS composition was also explored in this work. The only mineral phase of akaganeite with a uniform morphology of short rod was examined to be formed in all reaction treatments.These above results interpreted that formation, fate and growth conditions of iron oxyhydroxide in the natural environment are in the relation with the capacity of ferrous catalyzed oxidation and the regulation formation of iron minerals by extracellular polymeric substances, as well as the compositions of the reaction media. Extracellular polymeric substances exuded by bacteria play the key roles in the regulation formation of environmental mineral materials, which has evidently significance in environmental treatment, also is an evidence for the formation of natural mineral materials, and provides scientific gist for the produce and application of the novel environmental materials.