模拟表生环境中六方对称水钠锰矿的转化及其机制

Manganese oxide minerals are one of the important active components in soil and sediment. The crystal structures of manganese oxide minerals affect their physical and chemical properties and the transformation of manganese oxide minerals will directly influence their environmental geochemical behaviors, such as adsorption, oxidation, catalytic etc. Birnessite, layer structured manganese oxide, is widely distributed in earth surface environment. The formations of many other manganese oxides have close relations with birnessite, and many of them are formed directly or indirectly from birnessite. According to layer symmetry of birnessite, it can be divided into the hexagonal birnessite and triclinic birnessite, and natural birnessite always has hexagonal symmetry. So far most of studies focused on the transformation of triclinic birnessite or under certain harsh conditions. Hence, this project, under simulated surface environment, focuses the effect of earth surface environment(pH, type and concentration of ion, temperatures, clay minerals) and substructural characteristics of hexagonal birnessite (composition, the average manganese oxidation state, vacant Mn octahedron content, type and amount of interlayer cation ) on mineral transformation. The results will contribute to reveal the environmental geochemical behaviors of manganese oxide, and enrich surface environment mineralogy theory.

作为土壤与沉积物中的重要活性组分- - 氧化锰矿物，因结构不同，物理化学性质各异，不同氧化锰矿物间的转化影响其在表生环境中吸附、氧化、催化等行为。水钠锰矿是表生环境中广泛分布的层状氧化锰矿物，许多氧化锰矿物是以水钠锰矿为母体直接或间接转化生成。依据层结构的对称性，水钠锰矿分为六方对称型水钠锰矿（简称"六方水钠锰矿"）和三斜对称型水钠锰矿（简称"三斜水钠锰矿"），天然水钠锰矿主要为六方对称型。目前关于水钠锰矿转化的研究多以三斜水钠锰矿为母体，且多偏向于苛刻物理化学条件下的矿物转化。因此，本项目以六方水钠锰矿为前驱物，在接近表生环境条件下研究其亚结构特点（化学组成、锰氧化度、八面体空位数量、层间离子类型和数量等）和表生环境（pH、离子类型与数量、温度、共存粘土矿物等）变化对其转化的影响及其相关机制。研究将更贴近土壤表生环境，对深入揭示锰氧化物的环境地球化学行为、丰富表生矿物学理论具有重要意义。

六方水钠锰矿是表生环境中广泛分布的层状氧化锰矿物，许多氧化锰矿物是以水钠锰矿为母体直接或间接转化生成。目前关于水钠锰矿转化的研究多以三斜水钠锰矿为母体，且多偏向于苛刻物理化学条件下的矿物转化。本项目以六方水钠锰矿为前驱物，在接近表生环境条件下，通过X-射线衍射(XRD)、透射电镜(TEM/ED)、高分辨透射电镜(HRTEM)、扫描电镜(SEM/EDS)、红外光谱(IR)、光电子能谱(XPS)、热重分析(TGA)、全量分析、BET分析等技术，研究了六方对称型水钠锰矿亚结构特点（化学组成、锰氧化度、八面体空位数量、层间离子类型和数量等）和表生环境（pH、离子类型与数量、温度、共存粘土矿物等）变化对其转化的影响及其相关机制。探明了环境条件和前驱物亚结构特点与六方水钠锰矿转化的关系，初步探讨了六方水钠锰矿和锰钾矿降解染料和苯酚的特性。(1)明确了六方水钠锰矿亚结构特点对其自身转化产物及速率影响；(2)明确了表生环境变化对转化产物及速率的影响；(3)揭示了六方水钠锰矿矿物转变过程与机制。研究结果对揭示表生环境中六方水钠锰矿转化规律与机制，为探明不同氧化锰矿物成矿的相互关系，以及进一步预测和揭示水钠锰矿的环境地球化学行为、丰富表生土壤矿物学理论具有重要的理论与实际意义。