酸性矿山废水中施氏矿物的矿物学特性及其对As(V)和Cr(VI)的富集机制

Schwertmannite commonly occurs in sulfate-enriched acidic soils and acid mine drainage systems (AMD), its mineralogical properties affect and determine the accumulation behaviors towards contaminants. Due to its small particle size, poor crystallinity, and uncertainty of chemical composition, the formation and transformation properties of schwertmannite under various conditions have not been fully understood. Additionally, schwertmannite can extensively accumulate many contaminants, such as As(III/V) and Cr(VI), while the accumulation mechanisms are still unclear. Therefore, the objectives of this proposal are to (1) elucidate the kinetic processes and mechanism of schwertmannite formation under different environmental factors, such as Fe3+ hydrolysis rate, sulfate concentration, temperature, and pH, (2) explore the secondary mineralization properties of As(V)/Cr(VI) incorporated schwertmannite and the release mechanism of the contaminants in the presence of Al3+, Fe2+ or other reductive inducers, and (3) determine the speciation and accumulation mechanisms of As(V) and Cr(VI) in schwertmannite structure using several traditional and modern analytical techniques. The results are useful to explore the formation and transformation properties and crystal structure of schwertmannite, and its interaction mechanisms with contaminants. Also, it will provide scientific evidence for clarifying the environmental properties of schwertmannite and deeply understanding the source control of soil pollution.

施氏矿物常见于含硫酸盐的酸性土壤和酸性矿山废水（AMD）环境中，其矿物学特性影响和决定其对污染物的富集行为。由于颗粒尺寸小、结晶弱，结构组成不确定，对其在不同介质条件下的形成特点和转化机制了解甚少。此外，施氏矿物可大量富集有毒有害物质，如As(III/V)和Cr(VI)等，但富集机制仍不清楚。因此，本项目拟通过溶液化学方法结合现代分析技术，（1）探讨不同环境条件下，如Fe3+水解速率、SO42-浓度、温度和pH等因子，施氏矿物的形成动力学过程和机制；（2）揭示Al3+、Fe2+或其它还原诱导剂存在时，含As(V)/Cr(VI)施氏矿物的次生矿化特点和污染物释放规律；（3）阐明施氏矿物结构中As(V)和Cr(VI)的形态和富集机制。这些结果将有助于揭示AMD环境中施氏矿物的形成转化特点、晶体结构特性，及其与污染物的互作机制，为阐明施氏矿物的环境属性及土壤污染源头控制等提供科学依据。

本项目围绕AMD体系中施氏矿物（Schw）的形成与转化特性及其表面反应性开展研究：.1. 系统探究了通过Fe3+水解形成Schw及其转化过程。通过Fe3+水解-透析，纯Schw可在较宽的温度范围形成；透析时间越短和存在K+或NH4+可增强Schw结晶度。在Fe3+水解形成Schw过程中，含SO42-水铁矿为中间相。此外，随Fe3+水解速率减小，Schw的结晶度逐渐增加，其网状形貌更松散。在Schw转化过程中，高温、高pH、存在Fe2+和少量Cl-均加快转化成针铁矿，而低Fe3+水解速率和存在高量Cl-抑制转化。存在K+和高浓度NH4+有利于其转化形成黄钾铁钒，且NH4+效应更显著。.2. 深入揭示含Cr(VI)-Schw对As(III)的吸附-氧化行为与机制。随Schw中Cr(VI)含量增加，As(III)的去除率和氧化率均增加，且其吸附等温线更符合F方程。Schw界面催化As(III)和Cr(VI)之间反应，生成毒性更小的As(V)和Cr(III)，被Schw吸附固定。随反应pH增加，As(III)去除速率加快，但其氧化率却细微下降，这与高pH表面钝化有关。.3. 明确了As(V)和Cr(VI)在Schw表面的吸附机制及对SO42-配位环境的影响。As(V)表现出比Cr(VI)更高的吸附量，随pH增加，As(V)吸附量减小，而Cr(VI)吸附量增加。As(V)吸附涉及到SO42-和表面OH替代，Cr(VI)吸附主要替代SO42-。Schw表面As(V)和Cr(VI)的吸附形态最可能为双齿双核内圈配位，As-Fe和Cr-Fe原子间距分别为~3.29 Å和~3.36 Å。随As(V)吸附量增加或pH较小，As(V)表面沉淀逐渐形成和增加。As(V)或Cr(VI)吸附优先交换SO42-内圈配位，但不改变SO42-内圈配位结构。.这些结果为理解天然AMD体系中Schw的矿物学特性、Schw的表/界反应性提供了大量新的认识，且为预测和阐明与Schw相互胶结元素的生物有效性、迁移性和环境归属提供了科学依据。