Data_Sheet_1_U mobilization and associated U isotope fractionation by sulfur-oxidizing bacteria.pdf

Uranium (U) contamination of the environment causes high risk to health, demanding for effective and sustainable remediation. Bioremediation via microbial reduction of soluble U(VI) is generating high fractions (>50%) of insoluble non-crystalline U(IV) which, however, might be remobilized by sulfur-oxidizing bacteria. In this study, the efficacy of Acidithiobacillus (At.) ferrooxidans and Thiobacillus (T.) denitrificans to mobilize non-crystalline U(IV) and associated U isotope fractionation were investigated. At. ferrooxidans mobilized between 74 and 91% U after 1 week, and U mobilization was observed for both, living and inactive cells. Contrary to previous observations, no mobilization by T. denitrificans could be observed. Uranium mobilization by At. ferrooxidans did not cause U isotope fractionation suggesting that U isotope ratio determination is unsuitable as a direct proxy for bacterial U remobilization. The similar mobilization capability of active and inactive At. ferrooxidans cells suggests that the mobilization is based on the reaction with the cell biomass. This study raises doubts about the long-term sustainability of in-situ bioremediation measures at U-contaminated sites, especially with regard to non-crystalline U(IV) being the main component of U bioremediation.</p

Metal Mobilization by Iron- and Sulfur-Oxidizing Bacteria in a Multiple Extreme Mine Tailings in the Atacama Desert, Chile

The marine shore sulfidic mine tailings dump at the Chañaral Bay in the Atacama Desert, northern Chile, is characterized by extreme acidity, high salinity, and high heavy metals concentrations. Due to pyrite oxidation, metals (especially copper) are mobilized under acidic conditions and transported toward the tailings surface and precipitate as secondary minerals (Dold, <i>Environ. Sci. Technol</i>. <b>2006</b>, <i>40</i>, 752–758.). Depth profiles of total cell counts in this almost organic-carbon free multiple extreme environment showed variable numbers with up to 10⁸ cells g^–1 dry weight for 50 samples at four sites. Real-time PCR quantification and bacterial 16S rRNA gene diversity analysis via clone libraries revealed a dominance of <i>Bacteria</i> over <i>Archaea</i> and the frequent occurrence of the acidophilic iron­(II)- and sulfur-oxidizing and iron­(III)-reducing genera <i>Acidithiobacillus</i>, <i>Alicyclobacillus</i>, and <i>Sulfobacillus.</i> Acidophilic chemolithoautotrophic iron­(II)-oxidizing bacteria were also frequently found via most-probable-number (MPN) cultivation. Halotolerant iron­(II)-oxidizers in enrichment cultures were active at NaCl concentrations up to 1 M. Maximal microcalorimetrically determined pyrite oxidation rates coincided with maxima of the pyrite content, total cell counts, and MPN of iron­(II)-oxidizers. These findings indicate that microbial pyrite oxidation and metal mobilization preferentially occur in distinct tailings layers at high salinity. Microorganisms for biomining with seawater salt concentrations obviously exist in nature

Recovery of Nickel and Cobalt from Laterite Tailings by Reductive Dissolution under Aerobic Conditions Using <i>Acidithiobacillus</i> Species

Biomining of sulfidic ores has been applied for almost five decades. However, the bioprocessing of oxide ores such as laterites lags commercially behind. Recently, the Ferredox process was proposed to treat limonitic laterite ores by means of anaerobic reductive dissolution (AnRD), which was found to be more effective than aerobic bioleaching by fungi and other bacteria. We show here that the ferric iron reduction mediated by <i>Acidithiobacillus thiooxidans</i> can be applied to an aerobic reductive dissolution (AeRD) of nickel laterite tailings. AeRD using a consortium of <i>Acidithiobacillus thiooxidans</i> and <i>Acidithiobacillus ferrooxidans</i> extracted similar amounts of nickel (53–57%) and cobalt (55–60%) in only 7 days as AnRD using <i>Acidithiobacillus ferrooxidans</i>. The economic and environmental advantages of AeRD for processing of laterite tailings comprise no requirement for an anoxic atmosphere, 1.8-fold less acid consumption than for AnRD, as well as nickel and cobalt recovered in a ferrous-based pregnant leach solution (PLS), facilitating the subsequent metal recovery. In addition, an aerobic acid regeneration stage is proposed. Therefore, AeRD process development can be considered as environmentally friendly for treating laterites with low operational costs and as an attractive alternative to AnRD

Complexity of clay mineral formation during 120,000 years of soil development along the Franz Josef chronosequence, New Zealand

<p>Weathering of primary silicates to secondary clay minerals over time affects multiple soil functions such as the accumulation of organic matter and nutrient cations. However, the extent of clay mineral (trans)formation as a function of soil development is poorly understood. In this study, the degree of weathering of sediments along a 120 kyr soil formation gradient was investigated using X‐ray diffraction, Fourier transform infrared spectroscopy and X‐ray fluorescence spectroscopy. Irrespective of site age, mica and chlorite were the dominant clay minerals. During weathering, a remarkable suite of transitional phases such as vermiculite and several interstratifications with vermiculitic, smectitic, chloritic and micaceous layers developed. The degree of weathering was correlated with soil pH and depletion of K, Ca, Na, Fe and Al, regarding both soil depth and site age. Kaolinite occurred especially at the 120 kyr site, indicating slow formation via transitional phases. The findings of this study revealed that long-term soil development caused complex clay mineral assemblages, both temporally and spatially, and linking this variability to soil functioning warrants further research.</p