Oxyanion Surface Complexes Control the Kinetics and Pathway of Ferrihydrite Transformation to Goethite and Hematite,Environmental Science & Technology

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Oxyanion Surface Complexes Control the Kinetics and Pathway of Ferrihydrite Transformation to Goethite and Hematite
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2022-10-11 , DOI: 10.1021/acs.est.2c04971
Alireza Namayandeh ₁ , Olaf J Borkiewicz ₂ , Nefeli M Bompoti ₃ , Maria Chrysochoou ₃ , F Marc Michel _{1,

4}

Affiliation

The rate and pathway of ferrihydrite (Fh) transformation at oxic conditions to more stable products is controlled largely by temperature, pH, and the presence of other ions in the system such as nitrate (NO₃^–), sulfate (SO₄^2–), and arsenate (AsO₄^3–). Although the mechanism of Fh transformation and oxyanion complexation have been separately studied, the effect of surface complex type and strength on the rate and pathway remains only partly understood. We have developed a kinetic model that describes the effects of surface complex type and strength on Fh transformation to goethite (Gt) and hematite (Hm). Two sets of oxyanion-adsorbed Fh samples were prepared, nonbuffered and buffered, aged at 70 ± 1.5 °C, and then characterized using synchrotron X-ray scattering methods and wet chemical analysis. Kinetic modeling showed a significant decrease in the rate of Fh transformation for oxyanion surface complexes dominated by strong inner-sphere (SO₄^2– and AsO₄^3–) versus weak outer-sphere (NO₃^–) bonding and the control. The results also showed that the Fh transformation pathway is influenced by the type of surface complex such that with increasing strength of bonding, a smaller fraction of Gt forms compared with Hm. These findings are important for understanding and predicting the role of Fh in controlling the transport and fate of metal and metalloid oxyanions in natural and applied systems.

中文翻译：

氧离子表面络合物控制水铁矿转化为针铁矿和赤铁矿的动力学和途径

水铁矿 (Fh) 在含氧条件下转化为更稳定产物的速率和途径主要受温度、pH 值和系统中其他离子（例如硝酸盐 (NO ₃^– )、硫酸盐 (SO ₄^2– )）的存在控制, 和砷酸盐 (AsO ₄^3–). 尽管已经分别研究了 Fh 转化和氧阴离子络合的机制，但表面络合物类型和强度对速率和途径的影响仍然只有部分了解。我们开发了一个动力学模型来描述表面复合物类型和强度对 Fh 向针铁矿 (Gt) 和赤铁矿 (Hm) 转变的影响。制备了两组氧阴离子吸附的 Fh 样品，非缓冲和缓冲，在 70 ± 1.5 °C 下老化，然后使用同步加速器 X 射线散射方法和湿化学分析进行表征。动力学模型显示，由强内球（SO ₄^2-和 AsO ₄^3-）主导的氧阴离子表面复合物与弱外球（NO ₃^– ) 绑定和控制。结果还表明，Fh 转化途径受表面复合物类型的影响，因此随着结合强度的增加，与 Hm 相比，形成的 Gt 比例较小。这些发现对于理解和预测 Fh 在控制自然和应用系统中金属和类金属氧阴离子的运输和归宿方面的作用非常重要。

更新日期：2022-10-11

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