Earth System Science Institute, School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.
Environ Sci Technol. 2010 Jan 1;44(1):150-5. doi: 10.1021/es9010866.
Here we examine the bioreduction of technetium-99 in sediment microcosm experiments with varying nitrate and carbonate concentrations added to synthetic groundwater to assess the influence of pH and nitrate on bioreduction processes. The systems studied include unamended-, carbonate buffered-, low nitrate-, and high nitrate-groundwaters. During anaerobic incubation, terminal electron accepting processes (TEAPs) in the circumneutral pH, carbonate buffered system progressed to sulfate reduction, and Tc(VII) was removed from solution during Fe(III) reduction. In the high-nitrate system, pH increased during denitrification (pH 5.5 to 7.2), then TEAPs progressed to sulfate reduction. Again, Tc(VII) removal was associated with Fe(III) reduction. In both systems, XAS confirmed reduction to hydrous Tc(IV)O(2) like phases on Tc removal from solution. In the unamended and low-nitrate systems, the pH remained low, Fe(III) reduction was inhibited, and Tc(VII) remained in solution. Thus, nitrate can have complex influences on the development of the metal reducing conditions required for radionuclide treatment. High nitrate concentrations stimulated denitrification and caused pH neutralization facilitating Fe(III) reduction and Tc(VII) removal; acidic, low nitrate systems showed no Fe(III)-reduction. These results have implications for Tc-cycling in contaminated environments where nitrate has been considered undesirable, but where it may enhance Fe(III)-reduction via a novel pH "conditioning" step.
在这里，我们研究了在添加不同浓度硝酸盐和碳酸盐的模拟地下水中进行的 99Tc 生物还原的微宇宙实验，以评估 pH 值和硝酸盐对生物还原过程的影响。研究的系统包括未添加、碳酸盐缓冲、低硝酸盐和高硝酸盐地下水。在厌氧孵育期间，中性 pH 值碳酸盐缓冲系统中的末端电子接受过程（TEAPs）进展为硫酸盐还原，并且在 Fe(III)还原过程中 Tc(VII)从溶液中去除。在高硝酸盐系统中，反硝化过程中 pH 值升高（pH 5.5 至 7.2），然后 TEAPs 进展为硫酸盐还原。同样，Tc(VII)的去除与 Fe(III)的还原有关。在这两个系统中，XAS 证实了从溶液中去除 Tc 后，形成了水合 Tc(IV)O(2)类似物相的还原。在未添加和低硝酸盐系统中，pH 值保持较低，Fe(III)还原受到抑制，Tc(VII)仍留在溶液中。因此，硝酸盐对形成处理放射性核素所需的金属还原条件的发展可能具有复杂的影响。高硝酸盐浓度刺激反硝化作用并导致 pH 值中和，从而促进 Fe(III)还原和 Tc(VII)的去除；酸性、低硝酸盐系统则没有 Fe(III)还原。这些结果对于 Tc 循环在污染环境中具有意义，在这些环境中，硝酸盐被认为是不理想的，但它可能通过新的 pH“调节”步骤来增强 Fe(III)的还原。
