Department of Earth & Environmental Sciences, Rutgers University, 101 Warren Street, Newark, New Jersey 07102, United States.
Environ Sci Technol. 2023 Jun 6;57(22):8396-8405. doi: 10.1021/acs.est.3c01584. Epub 2023 May 23.
Batch kinetic experiments are combined with X-ray absorption spectroscopy (XAS) to compare the sorption of Mn(II), Co(II), Ni(II), Zn(II), and Cd(II) with sulfated green rust (GR) in anoxic pre-equilibrated suspensions at pH 8 over a timespan of 1 h to 1 week. The XAS data suggest that all five divalent metals coordinate at Fe(II) sites of the GR sorbent, whereas the batch results show that GR exhibits bimodal sorption behavior, with fast but limited uptake of Mn(II) and Cd(II) and much more extensive sorption of Co(II), Ni(II), and Zn(II) that continues throughout the entire experimental timeframe. We attribute these observations to differences in the affinity and extent of divalent metal substitution in Fe(II) sites of the GR lattice as controlled by ionic size. Divalent metals smaller than Fe(II) [, Co(II), Ni(II), and Zn(II)] are readily accommodated and undergo coprecipitation during GR dissolution-reprecipitation. In contrast, divalent metals larger than Fe(II) [, Mn(II) and Cd(II)] have a low affinity for substitution and remain coordinated at the surface following limited exchange with Fe(II) at GR particle edges. These results imply that GR may strongly affect the solubility of Co(II), Ni(II), and Zn(II) in reducing geochemical systems but will have little impact on the retention of Cd(II) and Mn(II).
批量动力学实验与 X 射线吸收光谱（XAS）相结合，比较了在无氧预平衡悬浮液中 pH 值为 8 时，Mn(II)、Co(II)、Ni(II)、Zn(II)和 Cd(II)与硫酸化绿锈（GR）的吸附作用，时间跨度为 1 小时至 1 周。XAS 数据表明，所有五种二价金属都与 GR 吸附剂中的 Fe(II)位点配位，而批量结果表明，GR 表现出双峰吸附行为，Mn(II)和 Cd(II)的吸附速度快但有限，而 Co(II)、Ni(II)和 Zn(II)的吸附则更加广泛，在整个实验时间内持续进行。我们将这些观察结果归因于 GR 晶格中 Fe(II)位点的二价金属取代的亲和力和程度的差异，这受离子大小的控制。小于 Fe(II)的二价金属[Co(II)、Ni(II)和 Zn(II)]很容易被容纳，并在 GR 溶解-再沉淀过程中发生共沉淀。相比之下，大于 Fe(II)的二价金属[Mn(II)和 Cd(II)]对取代的亲和力较低，并且在 GR 颗粒边缘与 Fe(II)进行有限交换后，仍在表面配位。这些结果表明，GR 可能会强烈影响还原地球化学系统中 Co(II)、Ni(II)和 Zn(II)的溶解度，但对 Cd(II)和 Mn(II)的保留影响不大。
