铝同晶替代对赤铁矿-Fe2+相互作用及其反应活性的影响

Fe2+ adsorbed on iron (oxyhydr)oxide mineral surfaces can promote recrystallization, and is much reactive in a series of redox reactions. Hematite is the most thermodynamically stable iron oxide in soils, and commonly contains Al impurity. Al substitution will greatly modify the structure and physicochemical properties of the mineral, e.g. the reactions between hematite and Fe2+ and related redox reactions involving contaminants. Here a combination of modern techniques and theories, including 57Fe tracer, 57Fe Mössbauer spectroscopy and X-ray absorption spectroscopy and so on, was used to investigate the atom exchange between Fe2+ and hematite substituted with different amounts of Al3+, including the extent of exchange and related factors and variations in the Fe local atomic environments. Further the interaction mechanisms of Al-substituted hematite-Fe2+ with typical inorganic (As3+, Cr6+) and organic (Roxarsone, Bisphenol A) pollutants were studied, the influencing factors (mineral morphologies, the concentration of Al3+ and Fe2+, coexisting pollutants) were discussed, the species and toxicity of intermediate and final reaction products were analyzed. Further the transformation and fate of pollutants in soils with different contents of hematite minerals induced by Fe2+ and related changes in iron oxide minerals were focused. These results can deepen our understanding of the reactivity of Al-substituted hematite minerals in soils, and can also help us in modeling and predicting the behaviors and fates of contaminants, and thus remediation and management.

吸附于铁氧化物表面的Fe2+可促使矿物重结晶，且具有强氧化还原反应活性。赤铁矿是土壤中最稳定的氧化铁矿物之一，其结构中普遍存在铝同晶替代。这将显著影响赤铁矿结构和化学反应特性，如与Fe2+相互作用及对污染物的氧化还原。本项目拟采用57Fe2+同位素示踪、穆斯堡尔谱、X射线吸收光谱等现代实验技术和方法，研究不同铝替代量赤铁矿与Fe2+的原子交换反应，分析原子交换率及影响因素、Fe原子局域环境变化等；通过铝替代赤铁矿-Fe2+体系对无机(As3+、Cr6+)和有机污染物(洛克沙胂、双酚A)等氧化还原反应的研究，探明形貌、Al含量、Fe2+含量、复合污染物等对反应的影响，分析污染物形态和毒性等的变化，明确不同赤铁矿含量土壤中57Fe2+诱导的污染物迁移转化和氧化铁矿物变化。研究结果有助于深入理解铝替代赤铁矿在土壤中的活性反应机制，亦可为土壤中污染物的行为预测、修复、治理等提供重要参考。

我国热带和亚热带土壤氧化铁矿物中广泛存在铝同晶替代，这会显著影响氧化铁矿物形貌、结构和表面反应特性，如Fe2+及污染物环境行为。本项目针对这一科学问题，取得的主要成果有：1. 铝同晶替代使赤铁矿晶体主要暴露由{101}、{112}、{110}和{104}变为{101}，导致其对Cr(VI)吸附量减少，且更多以单齿单核络合物形式吸附；亦使赤铁矿对As(III)吸附量总体呈下降趋势，仅有部分As(III)被氧化。2. 赤铁矿表面预吸附Fe2+能促进Cr(VI)吸附、还原和固定，且Al替代赤铁矿能去除更多Cr(VI)；尽管Fe2+使小部分预吸附在赤铁矿表面Cr(VI)释放，但是显著促进了Cr固定。3. 赤铁矿不同晶面对Al离子吸附亲和力大小顺序为{110} >{012} >{001}。4. 分析了湛江和长沙几种土壤中氧化铁矿物类型、含量及其铝替代量。不同土壤及胶体对Cr(VI)吸附量分别取决于有机质和氧化铁含量。土壤淹水培养后固体连续提取分级表明，土壤固定的Cr均为Cr(III)。培养45 d后，Cr主要以弱晶质和晶质氧化铁结合态存在。徐闻旱地和乌山林地针铁矿含量增加，徐闻水田中部分弱晶质铁氧化物转化成了针铁矿，而乌山水田氧化铁矿物变化不大。在徐闻旱地、乌山林地和乌山水田中TOC主要存在于晶质氧化铁结合态和残渣态中；徐闻水田中TOC在各组分含量基本相同。培养过程中，可交换态TOC逐渐减少，最后趋于稳定；而弱结晶铁氧化物结合态TOC逐渐减小。5. 针铁矿、赤铁矿和水铁矿表面吸附Cd2+过程中，固体表面富集轻同位素，且分馏量基本相同；但Cd同晶替代针铁矿则富集重同位素。6. Zn在针铁矿、纤铁矿和六方纤铁矿表面吸附过程中固体表面富集Zn重同位素。7. 探讨了赤铁矿光催化降解和赤铁矿在光照条件下活化亚硫酸盐降解洛克砂砷等有机污染物的过程和可能机制。这些研究结果促进了对土壤中氧化铁矿物界面污染物环境行为的理解，为污染物行为的模拟预测、修复和治理等提供重要参考。