锰代针铁矿的微生物还原机制及其环境意义

Goethite is one of the most common iron oxides on earth, ubiquitous occurred in soils, Fe-Mn crusts and sediments. Lots of research have shown that the formation and decomposition of goethite influence the geochemical cycle of other elements, in which the microbial reduction plays a key role. Natural goethite commonly contains metals in the form of isomorphism. For example, the common substitution of Fe by Mn makes substantial change to the mineralogical structure and surface reactivity of goethite. The existence of Mn also affects the microbial reduction of goethite and contributed to the formation of Mn-bearing secondary minerals, which have great environmental implications. By conducting mimic experiments on the microbial reduction of Mn-substituted goethite, this study intends to study the effect of the substitution of Mn for Fe on the contents and transformation paths of secondary minerals, as well as the redox evolution and geochemical fate of Fe and Mn. After that, we plan to study the effect of the substitution of Mn on the geochemical fate of heavy metals such as As and Pb in the microbial reduction of goethite. Thus, we aim to reveal the effect of microbial reduction of Mn-substituted goethite on the geochemical cycle of Fe, Mn, As, and Pb, as well as its environmental implications.

针铁矿是自然界最常见的铁矿物之一，广泛分布于土壤、铁锰结壳和沉积物中。大量研究表明针铁矿的形成和分解深刻影响着多种元素的地球化学循环，其中针铁矿的微生物还原发挥着关键作用。天然针铁矿中类质同像现象十分普遍，常见的Mn-Fe替代改变了针铁矿晶体结构和表面反应性，变价元素Mn的加入对针铁矿微生物还原作用亦有重要影响，并且会形成一系列具有重要环境意义的含锰次生矿物。本项目拟通过锰代针铁矿微生物还原模拟实验，系统研究Mn-Fe替代对针铁矿微生物还原次生矿物组成和矿物物相转变顺序的影响，确定Fe、Mn元素氧化还原状态演化和赋存形式变化规律。在此基础上，揭示Mn替代对针铁矿微生物还原过程中As、Pb赋存状态和环境行为的影响机制，阐明锰代针铁矿微生物还原对Fe、Mn、As、Pb等元素地球化学循环的影响及其环境意义。

天然针铁矿往往含有杂质元素，常见的有锰代针铁矿，锰替代可改变针铁矿的矿物结构及其表面反应性。本项目通过合成不同锰含量锰代针铁矿，并开展了矿物学表征，结果表明锰替代改变了针铁矿晶胞参数并降低其带隙，结合理论计算和实验模拟结果得到晶体能量最低的锰替代含量，并用实验得到了验证其表面催化效应。在此基础上，开展了锰代针铁矿和Fe(II)离子相互作用模拟实验，研究了锰代针铁矿还原过程中重金属砷的释放和迁移规律，利用同步辐射技术揭示其微观络合机制。开展了铁锰共存条件下微生物还原模拟实验，分析了砷释放及不同形态砷的变化规律，探究了锰对次生矿物和砷形态的影响。这一研究有助于理解自然环境中天然针铁矿中锰替代对其影响环境中Fe、Mn、As元素地球化学循环的重要作用。