Biological And Chemical Synthesis Of FeOOH And Their Roles On Removal Of Heavy Mental

Acidithiobacillus ferrooxidans (A. ferrooxidans), an acidophilic chemolithoautotroph, can use ferrous iron, reduced sulfur species, or metal sulfides as energy sources. In bioleaching of pyrite-rich ores, bacterial pyrite oxidation leads to production of the iron- and sulfate-rich acid mine drainage (AMD). The mixing of AMD with other types of water results in deposition of abundant iron oxyhydroxides in natural environments. It has been demonstrated that iron oxyhydroxides can effectively scavenge heavy metals by adsorption, coprecipitation, and structural incorporation/substitution.The capacity of iron oxyhydroxides for scavenging metals is strongly correlated with their morphology, size and crystallinity such as schwertmannite, goethite, akaganeite and lepidocrocite. Due to phases transform and environmental function of minerals are tightly related to morphology structures, interface properties and the conditions and methods of synthesis of minerals, it is necessary that their structural interface properties are characterize for iron oxyhydroxides, to provide thoretical proofs of the function mechanism being in the both iron minerals and contaminates.Therefore, in the present paper we conducted a series of culture experiments to isolate such a potential A. ferrooxidans bacterium from sewage sludge and growth process of As(Ⅲ) removal efficiency; using the modified 9K medium with FeSO4·7 H2O as energy. Also, using different ways such as ferrous biooxidation, ferric hydrolysis and neutralization and ferrous oxidation by air, iron oxyhydroxides with the different phase were chemically synthesized. The above resulting products of iron oxyhydroxides are characterized by spectral methods to examine their phases and structural properties. The other group of experiments that some of the characterized FeOOH are applied to remove Cr(Ⅵ) were carried out. The expected results provide a scientific proof for searching the potential adsorbent materials.The results of all works are presented as following:The bacterium XH3 could completely oxidize ferrous iron into ferric iron at the moderate temperatures of 28-35 ℃ (at an initial pH of 2.8) and was independent of pH values in the range of 2.0 to 3.3 (at 28℃). Under the adapted culture conditions of an initial pH of 2.8 and 28℃, all Fe2+ can be completely oxidized within 48h. The affect of As(Ⅲ) addition on growth of the strain XH3 showed that the ferrous could be completely biooxidized into ferric in the cultures initially with 0.1-0.8 g/L As and occurrence of bacterial accommodation to As at the higher levels of 0.5-08 g/L was observed, but the highest level (1.2 g/L) of As had a obvious resticting to ferrous bioxidization. The higher As removal percent could be obtained in the bacterial culture initially with the level of 0.8 g/L.Because of the independent of pH2.0-3.3 for a better bacterial growth and the lower chemical oxidation of ferrous iron under pH4.2, the related experiments on ferrous oxidation in the reaction solutions with A.ferrooxidans cells under pH4.2 operated, it showed that addition of A. ferrooxidans could accelerate the oxidation rate of Fe2+ as FeSO4, and had little affect on goethite formation, which showed that the mineral phase, crystallinity and particle morphology all couldn’t be effected.Chemically synthetic iron precipitation products under the corresponding reaction conditions identified by XRD and FTIR as α,β,γ-FeOOH minerals, had the particle morphology of thin needle for α-FeOOH and nanoparticle morphology of short rod for β,γ-FeOOH. Due to the case that differences of the structural surface groups such as hydroxyl and characteristic groups for α,β,γ-FeOOH have great impact on the environment, adsorption of Cr(Ⅵ) on the minerals of FeOOH in reaction solutions were further studied.Results showed that α,β,γ-FeOOH had a high capacities of Cr(Ⅵ) adsorption, and a higher removal efficiency for α,β,γ-FeOOH when their pH values of reaction solutions ranged in 2-6, 6-9 and 3-7, respectively. Herein, basing the above results and the general pH 4-6 for the polluted wastes rich in Cr, the selected pH5-7 for the next experiments on Cr(Ⅵ) adsorption by α,β,γ-FeOOH, it showed that Cr(Ⅵ) adsorption on FeOOH was beserved to be a fast speed: 50% of removal efficiency after 5 minutes of adsorption equilibrium time, and 95% of the higher efficiency after 1 hour. The data on isothermal adsorption of Cr(Ⅵ) by α,β,γ-FeOOH can be fitted by Langmiur and Freundlich equations, which showed a good correlativity. The ionic strength and the commonly coexisting anions such as Cl- and NO3- in reaction solutions hardly had effect on Cr(Ⅵ) removal, while the other anions of SO42-and PO43- and their concentrations had the greater impact on the removal results of Cr(Ⅵ) adsorption by FeOOH.Obviously, the chemical and physical properties of adsorption materials have great impacts on the environment. The above study results can provide the academic gist for the formation and phase translation of iron minerals in natural environments, and the science evidence for the research development and application of the environmental materials.