Inducing magnetite formation by microbial Fe(II) oxidation in the presence of mineral nucleation sites: Evaluating a novel approach to heavy metal remediation in the environment.

生物源磁铁矿（Fe3O4）纳米颗粒是由Fe（III）还原菌在环境中产生的Fe(II)/Fe（III）矿物混合而成，具有小尺寸（<50 nm）、高活性Fe（II）表层和有机包被。所有这些特性使得生物磁铁矿适合潜在的修复策略。铁（II）氧化细菌通常不与磁铁矿的形成有关，相反，铁（III）氢氧化物如针铁矿（α - feooh）和水合铁（简化为Fe(OH)3）更常产生。我们小组最近的工作表明，在微生物Fe（II）氧化过程中，少量磁铁矿纳米颗粒的存在可以作为成核位点，并导致额外磁铁矿的形成。目前尚不清楚这种新的磁铁矿是由自发形成的核组成，还是由增加的成核位置生长的更大的颗粒组成。为了将微生物来源的生物磁铁矿用于修复目的，需要了解磁铁矿的形成机制及其反应性。因此，我们建议用Fe（II）氧化细菌进行实验，以详细研究成核位点的影响，并选择一些变量，包括比表面积和成核位点浓度，以观察磁铁矿形成速率和最终矿物相产生的变化。此外，我们建议进行批量实验，以测试生物源磁铁矿对有毒金属（如砷和铬）的修复作用，从而有效地将离子锁定在河流下潜带沉积物中的磁铁矿中。其目的是制定战略，修复对世界各地数百万人构成严重健康风险的受污染土地和水。

Biogenic magnetite (Fe3O4) nanoparticles are mixed Fe(II)/Fe(III) minerals produced in the environment by Fe(III)-reducing bacteria with small size (<50 nm), a highly reactive Fe(II) surface layer and an organic coating. All of these properties make biogenic magnetite suitable for potential remediation strategies. Fe(II)-oxidizing bacteria are not ordinarily found associated with the formation of magnetite, instead Fe(III) oxyhydroxides such as goethite (alpha-FeOOH) and ferrihydrite (simplified as Fe(OH)3) are more commonly produced. Recent work by our group has shown that the presence of small amounts of magnetite nanoparticles during microbial Fe(II) oxidation can act as nucleation sites and lead to the formation of additional magnetite. It is not known if this new magnetite consists of spontaneously created nuclei or larger particles growing from the added nucleation sites. To apply microbially derived biogenic magnetite for remediation purposes, the mechanism of magnetite formation and its reactivity need to be known. We therefore propose experiments with Fe(II)-oxidizing bacteria to study the impact of nucleation sites in detail, with a number of variables including specific surface area and concentration of nucleation sites chosen to observe changes in the rate of magnetite formation and in the final mineral phases produced. Additionally, we propose batch experiments to test the biogenic magnetite for remediation of the toxic metal(loid)s arsenic and chromium to effectively lock-in the ions into the magnetite with sediment from the hyporheic zone of a river. This will be aimed towards developing strategies for remediation of contaminated land and water that pose serious health risks to millions of people around the world.