Formation Of Biogenic Iron Minerals And Their Adsorption Capacities To Heavy Metals

Acidithiobacillus ferrooxidans (A. ferrooxidans) present in acidic environments can promote the second ferric oxyhydrooxides mineral phases of schwertmannite and jarosite. These biogenic iron oxyhydrooxides can scavenge the heavy meatals and other toxic elements from the polluted water environments by the function mechanisms of adsorption, coprecipitation, substitution of structural elements. Iron bacteria may biocatalyze of ferrous oxidation and poromote ferric assembling. The extracellural polymeric substances (EPS) excreted by iron bacteria can complex ferric ions formed iron minerals by hydrolyzation, precipitation, and stabilization. These biogenic iron minerals are the important intermediary in the interaction of "microbiology-mineral-environment". Their biomineralization is related to A. ferrooxidans and EPS.Biomineralization of iron minerals usually are affected by the environmental temperature and pH value, the components (such as organism of surfactants, anions of Cl- and SO42-, and cations of K+、Na、NH4+) from the medium solutions. Therefore, in the present paper, the influence of nonionic surfactants, heavy metals of As(Ⅲ)/Cr(Ⅲ) on the formation of iron mineral and their removal capacity to polluted elements in the cultivation media and bacterial EPS solutions, to uncover biomineralization principle and mechanism on removing pollutates. The results of all studies are as follows:There is little impact by nonionic surfactants at the moderate concentration present in bacterial cultures on bacterial Fe2+ oxidation ability. Under the action of 50mg/L Tween 80, "pincushions" covered the immediate products of schwertmannite spheroid particles formed in bacterial cultures show the bind-like morphology, which shows that there is the function by Tween 80 on morphology and structure of biogenic iron minerals.In the bacterial cultures containing 0-0.6g/L As(Ⅲ) or 0-0.8g/L Cr(Ⅲ),almost content of initial Fe2+ could be completely oxidized into Fe3+ during the period following bacterial acclimatization time phase. There is an irrevocable inhibition by 0.9g/L As(Ⅲ) or high than 0.8g/L Cr(Ⅲ) on bacterial Fe2+ oxidization ability. Under the function of 50mg/L Tween 80, bacterial acclimation to As(Ⅲ)/Cr(Ⅲ) and Fe2+ oxidization ability can be enhanced, and it make that the removal percent of As(Ⅲ) increase to 70-95% from 60-85%,while the removal percent of Cr(Ⅲ) increase to 50-65% from 60-65%.In bacterial EPS solutions containing 0-120mg/L As(Ⅲ) or 0-250mg/L Cr(Ⅲ), the phase of iron minerals can be transformation as increasing of reaction time, and the formation of iron mineral can be promoted by EPS. There is an irrevocable inhibition by 0.9g/L As(Ⅲ) or 0.8g/L Cr(Ⅲ) on bacterial Fe2+ oxidization ability. The phase transformation of iron minerals is inhibited by the higher As(Ⅲ) concentration of 80mg/L(28℃) or 120mg/L(40℃). The particular morphology of iron mineral products is impacted by external As(Ⅲ)/Cr(Ⅲ). When the reaction temperature is increased, there are the positive effects on the formation/transformation and the action of As(Ⅲ), while there is little impact on the action of Cr(Ⅲ). A few As(Ⅲ)/Cr(Ⅲ) is removed during the whole reaction phase for all systems, due to trace iron mineral formed.In bacterial EPS solutions added external 1.5 mol/L of Na+ or NH4+ with a molar ratio of Cl/SO4 (0,1,3,6, or 10), the phase of iron minerals can be transformation as increasing of reaction time, and the formation of iron mineral can be promoted by EPS. The different molar ratio of Cl/SO4, and Na+/NH4+ can influence the phase transformation and particle morphology the produced iron minerals.