水锰矿与Fe^2＋的相互作用与转化过程

Interaction and transformation processes of manganite and Fe^(2+)

作为表生土壤环境中易生成且分布广泛的氧化锰矿物,水锰矿(γ-MnOOH)能参与铁氧化物的生成过程,影响Fe_(2+)的迁移、转化和归趋。本文考察了pH值为3.0~7.0的模拟水溶液体系中水锰矿与Fe_(2+)的相互作用及其生成铁氧化物的过程,分析了Fe_(2+)浓度、pH值和空气(氧气)对Fe(Ⅲ)氧化物晶体结构类型、化学组成和反应速率的影响。研究结果表明,水锰矿氧化Fe_(2+)产物主要为针铁矿和纤铁矿;pH值为3.0~5.0时产物为针铁矿,而pH值为7.0时产物为针铁矿与纤铁矿的混合物,且高浓度Fe_(2+)会促使纤铁矿生成;引入空气利于针铁矿生成;反应速率随着pH值升高、氧气分压的增大而加快。本工作丰富了对铁氧化物在常见锰氧化物表面形成和转化过程的认识。

As one of the common manganese oxides easily generated and widely distributed in the supergene environment, manganite participates in the formation of Fe（Ⅲ） oxides, affecting the migration, transformation and fate of Fe2＋ in aqueous systems. In this study, the redox mechanism was studied by determining the intermediates, and the influence of initial pH and air（oxygen） on the processes was studied in simulated aqueous systems with pH value in the range of 3-0~7.0. The influence of Fe2＋ concentration, pH value, and air（oxygen） on ferric（hydr） oxide crystal strucutres, chemical compositions and the redox rate was studied in closed and open aqueous systems. The results indicate that goethite and lepidocrocite are formed as the major products of Fe2＋ oxidation by manganite. Goethite and lepidocrocite tend to be formed when pH values are controlled at 3.0~5.0 and 7.0, respectively. High concentration of Fe2＋ facilitates the formation of lepidocrocite. The introduction of air（oxygen） is convenient for the generation of goethite of high crystallinity. The redox rate of manganite and Fe2＋ increases with the increase of pH value and oxygen partial pressure in reaction systems. The present study facilitates the understanding of the natural genesis of ferric oxides on the surface of manganese oxides.