Iron(III)-precipitates formed by the oxidation of dissolved Fe(II) are important sorbents for major and trace elements in aquatic and terrestrial systems. Their reductive dissolution in turn may result in the release of associated elements. We examined the reductive dissolution kinetics of an environmentally relevant set of Fe(II)-derived arsenate-containing Fe(III)-precipitates whose structure as function of phosphate (P) and silicate (Si) content varied between poorly-crystalline lepidocrocite, amorphous Fe(III)-phosphate, and Si-containing ferrihydrite. The experiments were performed with 0.2-0.5 mM precipitate-Fe(III) using 10 mM Na-ascorbate as reductant, 5 mM bipyridine as Fe(II)-complexing ligand, and 10 mM MOPS/5 mM NaOH as pH 7.0 buffer. Times required for the dissolution of half of the precipitate (t50%) ranged from 1.5 to 39 h; spanning a factor 25 range. At loadings up to ~ 0.2 P/Fe (molar ratio), phosphate decreased the t50% of Si-free precipitates, probably by reducing the crystallinity of lepidocrocite. The reductive dissolution of Fe(III)-phosphates formed at higher P/Fe ratios was again slower, possibly due to P-inhibited ascorbate binding to precipitate-Fe(III). The slowest reductive dissolution was observed for P-free Si-ferrihydrite with ~ 0.1 Si/Fe, suggesting that silicate binding and polymerization may reduce surface accessibility. The inhibiting effect of Si was reduced by phosphate. Dried-resuspended precipitates dissolved 1.0 to 1.8-times more slowly than precipitates that were kept wet after synthesis, most probably because drying enhanced nanoparticle aggregation. Variations in the reductive dissolution kinetics of Fe(II) oxidation products as reported from this study should be taken into account when addressing the impact of such precipitates on the environmental cycling of co-transformed nutrients and contaminants.

中文翻译：

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Fe（II）氧化形成的含As（V）的Fe（III）沉淀在水溶液中的还原溶解。

由溶解的Fe（II）氧化形成的铁（III）沉淀物是水生和陆地系统中主要和微量元素的重要吸附剂。它们的还原溶解反过来可能导致相关元素的释放。我们研究了环境相关的一组Fe（II）衍生的含砷酸盐的Fe（III）沉淀物的还原溶解动力学，其结构随磷酸盐（P）和硅酸盐（Si）含量的变化而变化，其结晶度较差的纤铁矿，无定形磷酸铁（III）和含硅的水铁矿。实验使用0.2-0.5 mM沉淀-Fe（III），使用10 mM抗坏血酸钠作为还原剂，5 mM联吡啶作为Fe（II）络合配体，以及10 mM MOPS / 5 mM NaOH作为pH 7.0缓冲液。溶解一半沉淀物（t50％）所需的时间为1.5至39小时；跨越25倍的范围。在最高〜0.2 P / Fe（摩尔比）的加载量下，磷酸盐可能会降低纤铁矿的结晶度，从而降低无硅沉淀物的t50％。以较高的P / Fe比形成的Fe（III）-磷酸盐的还原溶解速度再次变慢，这可能是由于P抑制的抗坏血酸盐与沉淀物-Fe（III）的结合。对于含〜0.1 Si / Fe的无磷硅铁水合物，观察到的还原溶解最慢，这表明硅酸盐的结合和聚合反应可能会降低表面可及性。磷酸盐降低了Si的抑制作用。干燥后重悬的沉淀物的溶解比合成后保持湿润的沉淀物的溶解速度慢1.0至1.8倍，这最有可能是因为干燥增强了纳米颗粒的聚集。