흡착된 산화음이온 종에 따른 슈베르트마나이트의 안정성

초록

In acid mine drainage (AMD) environments, various precipitated iron (oxyhydr)oxide minerals can attenuate oxyanion-forming heavy metals through co-precipitation and surface adsorption. However, subsequent mineral phase transformations may induce additional changes in the mobility and stability of these ions. Schwertmannite, a poorly crystalline, metastable mineral with high specific surface area and sorption capacity, typically transforms into goethite over time. The influence of adsorbed oxyanions on the kinetics of this transformation, however, remains insufficiently understood. In this study, five oxyanions (AsO4, CrO4, SeO3, SeO4, MoO4) were each adsorbed onto schwertmannite at an equivalent loading of 0.5 mmol/g. The transformation of these oxyanion-laden schwertmannite samples into goethite was systematically investigated and compared to that of pure schwertmannite under controlled conditions (pH 9, 30℃) over 14 weeks using pH monitoring, cumulative OH consumption, and X-ray diffraction (XRD) analyses. The results indicate that unmodified schwertmannite underwent the fastest transformation into goethite, followed by SeO4-adsorbed schwertmannite, likely due to its structural similarity to SO4 and its formation of outer-sphere complexes. In contrast, AsO4, CrO4, SeO3, and MoO4 significantly delayed the transformation due to the formation of strong inner-sphere surface complexes. These findings highlight the critical role of oxyanion binding mechanisms in controlling the structural stability and transformation behavior of schwertmannite, offering valuable insights into the long-term fate of oxyanionic contaminants in AMD-impacted environments.

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