Study On Phase Transfermation Of Iron Oxyhydroxides By The Catalytic Action Of Aqueous Fe(Ⅱ) In An Anoxic Enviroment

Iron oxides/oxohydroxides are common compounds which are widespread in nature. They are presence in almost all of the different compartments of the global system—he atmosphere, hydrosphere, lithosphere, pedosphere and biosphere, etc. Iron oxides/oxohydroxides are the main products of the collision of steels in natual. A variety of transformations between different species can take place because of their different thermodynamic stability in the special dictions.In recent years, research on the reductive dissolution of iron (hydr)oxides in the presence of Fe(II) or other organic or inorganic reductants reveals the catalytic nature that Fe(II) etc. can accelerate the dissolution of iron (hydr)oxides. According to the character of catalysts, we guess that Fe(II) or other reductants can also catalyze the formation of iron oxides. On the basis of our study on the preparation of iron oxide, we have verified the catalytic action of Fe(II) on the formation of iron oxide and applied it to the synthesis of hematite particles. That is, a new pathway to prepare nanosized hematite particles has been found. This new method is called liquid catalytic phase transformation.This paper is aimed at researching in detail the phase transfer mechanism of the hydroxides. The research will contribute to the recognition for the formation mechanism of iron oxides in natural environment because the formation condition of iron oxides in present work is very similar to that in natural environment.The research in this part was focused on the phase transformation mechanism of the differt phases of FeOOH in the presence or absence of trace Fe(II) in near neutral pH under low temperatures.The main contents as follows:(1) The preparation of four different phases of FeOOHThrough the literature survey and previous research,we prepared the four different phases of FeOOH by the relatively simple methods.(2) Using the prepared phases as the precursor, we study their aging reactions in the presence or absence of trace Fe(II) at near neutral pH at low temperatures. The results indicated that:both δ-FeOOH and γ-FeOOH would have phase transfration in the aging and finally change into α-FeOOH, the temperature is higher,the reaction rate is faster. In the presence of trace Fe(II) at neutral pH made the rate faster. It shows that the phase transformation mechannism is the dissolution-reprecipitation mechanism. However, there are not the phase transfemation while β-FeOOH and a-FeOOH is in the same conditions.