Experimental Study On Micribial Oxidation Of Mn (Ⅱ)

Microbe-mineral interactions affect the geochemical behaviors of a variety of elements in supergene environments. It has been proved that biogenic manganese minerals has important environmental significance and resource values. Predecessors have conducted a great deal of studies on microbial oxidation of manganese. Most studies focused on the geological conditions of the microbial manganese mineralization. It has important theoretical significance to reveal the microscopic mechanism of microbe-mineral interactions as well as the mineral teansformation path of manganese in the sedimentary mineralization and secondary weathering processes.In this thesis, the microbial oxidation and mineralization of Mn2+ ions by Pseudomonas putida CGMCC 1.3136 which is isolated from soils has been investigated. In addition, we explored dissolution of the Mn(II)-bearing mineral rhodochrosite (MnCO3) and characteristics of ensuing Mn oxides by Mn(II)-oxidizing bacterium Pseudomonas putida MnB1. This thesis intends to focus on the oxidation process of manganese element, the types and sequence of biogenic manganese minerals in order to discuss the microbial oxidation mechanism of manganese. A series of bath experiments were carried out, including at least three groups of bio-Mn, heated-bio-Mn, and Mn. Here "bio-" represents the inoculation of 10 mL of solution with ～107 cells/ml, and "heated-bio-Mn" means sterilization for the bacterium solution at 80℃ for 30 minutes before inoculation. "Mn" denotes the addition of MnCl2 or rhodochrosite (MnCO3) into 100 mL medium. The bio-Mn groups were set up to assess the microbial oxidation of Mn(II).Through ICP-OES and spectrophotometric method, we studied and contrasted manganese concentration changes in experiment systems, and found that bacteria notably implemented the oxidation and mineralization of manganese. By using SEM, TEM, XRD, STXM and FTIR etc. methods, an array of manganese oxides were tested. So we drew the following two main conclusions:1. A two-stepped model is a feasible explanation for this experiment of mineralization and oxidation of Mn2+. In the first step, the primary product of microbial oxidation of Mn2+ ions is birnessite or birnessite-like mineral and then transformed into feitknechtite and hausmannite as the Mn2+ concentration of the experimental solution was as high as 5.0 mmol/L. In this second step, the Mn2+ ion appears as a reductant for the reducing of biogenic Mn(Ⅳ) oxides and can ensure the stability of Mn(Ⅲ) secondary precipitates.2. In microorganisms and rhodochrosite interaction system, the microorganisms form biofilms on mineral surface to form a special interface environment, so that the minerals are dissolved, and the Mn2+ along with other ions would be adsorbed and oxidized by cells in suspension or biofilm. Moreover, secondary minerals are mixed with organic matter.Combined with previous findings, we suggest that Mn(Ⅱ) oxidation involves a complex network of abiotic and biotic processes.