Iron Oxide Minerals Phase Transformation Catalyzed By Fe(â…¡) And Its Effect On Heavy Metals Fixation

In anaerobic soil ervironment, Fe(â…¡)-Fe(â…¡I) cycle is an important driving force of matter and energy transformation. The abiotic Fe(â…¡) or Fe(â…¡I) adsorbed to soil interface with a lower redox potential and higher chemical reduction ability that could promote the heavy metal contaminants transformation in the environment. Meanwhile, Fe(â…¡) also can react with the iron oxides in the soil, as a large number of amorphous iron oxides in the soil which could be catalyzed by Fe(â…¡) and converted to a higher degree of crystallinity mineral, in this process, contaminants in the envinonment can be adsorbed and fixed into the iron oxides, and then reduce the available concentration of pollutants in environmental.In my thesis we designed anaerob ic batch experiments, to discuss the Fe(â…¡)/Fe(â…¡I) cycle during the Fe(â…¡) catalyzed iron oxides crystal phase transformation or Fe(â…¡) catalyzed Al substitution iron oxides crystal phase transformation, because Al structure of iron oxides in the soil environment replaces this general phenomenon based on environmental mineralogy. To further reveal the natural reduction of pollutant conversion process, and provided the basis for the develop ment of soil pollution control technology. The main conclusions are as followed:We employed 57 Fe isotope tracermethod to research the reaction mechanism between aqueous Fe(â…¡) and the hematite In anaerobic system. This results indicated that there is signifinant Fe atom exchange between aqueous Fe(â…¡) and hematite structure in state Fe(â…¡I), namely aqueous Fe(â…¡) entered into hematite structure forming Fe(â…¡I), but hematite structure in state Fe(â…¡I) reduction is released into the solution system to form a free state Fe(â…¡). The reaction system is affected by the rate of e xchange of Fe atoms and the pH of the aqueous Fe(â…¡) of initial concentration, as compared with the acidic environment, pH 7.5 neutral environment is inclined to the Fe atom exchange occurs; pH value in the same conditions next, Fe atoms exchange rate increaseswith the free state of Fe(â…¡) initial concentration. More importantly, characterization by means of X-ray diffraction and Mossbauer spectroscopy and other structures, we observed hematite crystal phases in the process of restructuring the new hematite and goethite, description free state Fe(â…¡) into iron oxide structure, the majority through the homoepitaxial growth mechanism of crystal formation of a new hematite crystal, and partly by hetero-epitaxial growth mechanism of the formation of goethite.Stable nature of hematite iron oxide occurs phase transformation.During ferrihydrite transformation catalyzed by Fe(â…¡), rare earth metal ions compete sorption site of ferrihydrite with Fe(â…¡). However, the mechanism of the metal ions with different logK effect the rate and pathway of ferrihydrite transformation is still unclear. Here, we selected six different heavy metal ions disclose the mechanism. This results indicated that the logK of different heavy metal ions effect the distribution of heavy metal ions and Fe(â…¡) species, and also influence the Ep of active Fe(â…¡), which fundamentally effect the atomic exchange and electron transfer between Fe(â…¡) and ferrihydrite, then control the path and rate of ferrihydrite transformation.During Al substitution ferrihydrite transformation catalyzed by Fe(â…¡), metal ions compete sorption site of ferrihydrite with Fe(â…¡). Here, we selected two different heavy metal ions disclose the mechanism. This results indicated that the different heavy metal ions and different proportions Al substitution control the path and rate of iron oxides transformation. During the Fe(â…¡)- induced Al- ferrihydrite transformation, less divalent cation of Cd(â…¡) were stabilized in Al- ferrihydrite compared with the thivalent cation of Cr(â…¡I), much of which were adsorbed on and structurally stabilized in the transformed iron oxides. Al- ferrihydrite with higher ratio of substituted Al stabilized more cations. The same trivalence and the more similar ionic radius of Cr(â…¡I) with that of Al and F e in the Al- ferrihydrite lead to higher incorporation of Cr(â…¡I) in formed secondary iron minerals from the Fe(â…¡)-induced transformation of Al- ferrihydrite, compared with that of Cd(â…¡).