【作者】 谭军凤；

【导师】 刘凡；

【作者基本信息】 华中农业大学 ， 环境工程， 2008， 硕士

【摘要】 氧化锰矿物对Cr等变价元素的氧化是影响其土壤环境行为的重要过程。国内外针对氧化锰氧化Cr（Ⅲ）的研究多限于少数高价矿物,以考察热力学特性和Cr形态变化为主,对动力学过程、中间产物、电子传递等反应途径却较少关注。最近已探明,氧化锰生物形成过程中生成的Mn（Ⅲ）是环境Mn（Ⅲ）的重要来源,Mn（Ⅲ）氧化活性更强,可能具有更重要的环境效应。而土壤中不同价态氧化锰在发生诸多氧化反应中是否也产生Mn（Ⅲ）并作为环境Mn（Ⅲ）的又一重要来源?尚无定论。因此深入探讨不同价态氧化锰氧化Cr（Ⅲ）的动力学过程和反应途径,这对阐明Cr的环境行为、氧化锰的反应机制及Mn（Ⅲ）的来源、作用与环境效应有重要意义。本文探讨了实验室合成的碱性水钠锰矿对Cr（Ⅲ）的反应条件以及Mn（Ⅲ）在氧化过程中的重要性。取得的主要结果有:1、Mn（Ⅲ）在Cr（Ⅲ）氧化过程中具有重要作用,且对Cr（Ⅲ）氧化速率影响较大的并非矿物空穴上下方和层间的Mn（Ⅲ）,而是Mn（Ⅳ）→Mn（Ⅲ）电子转移过程后的Mn（Ⅲ）。反应的限速步骤为Mn（Ⅳ）→Mn（Ⅲ）的电子转移过程。2、矿物中的Mn（Ⅲ）被络合后,可以提供更多的位点供Cr（Ⅲ）吸附;且反应体系中的Mn（Ⅲ）经Na₄P₂O₇络合后,几乎只有Mn（Ⅳ）参与反应。Mn（Ⅲ）→Mn（Ⅱ）电子转移过程受到抑制的同时,会促进Mn（Ⅳ）→Mn（Ⅲ）电子转移过程。3、与Mn（Ⅲ）相关的反应途径对Cr（Ⅲ）氧化反应速率的贡献大于Mn（Ⅲ）无关的反应途径。价态越高的氧化锰矿物是仅具有基于热力学平衡上较大的氧化容量,而非动力学基础上的氧化速率。更多还原

【Abstract】 Manganese oxide is known to oxidize the variable valence elements to change their soil environmental behavior,such as Cr.Although many different manganese oxides have been shown to oxidize Cr（Ⅲ）,the most common oxides are in high valence,and the main purpose is for thermodynamic properties and valence change of Cr.Despite considerable research,the mechanism of dynamic process,intermediate products and electron transformation are still unclear.Some recent studies have proven that Mn（Ⅲ） producing during the process of generating biogenic manganese oxides is an important source of Mn（Ⅲ） in environment,and it is possibly that Mn（Ⅲ） has some more crucial environmental impact for its high activity.Consequently,Mn（Ⅲ） appearing during the oxidation by mixed valence manganese oxides may also play an important role in nature, yet the detailed mechanism remains incompletely understood.For explaining the environmental behavior of Cr,it is significant to conduct extensive investigation of Cr（Ⅲ） oxidation by mixed valence manganese oxides to make clear of the dynamic process, reaction pathway,oxidation mechanism,the vital role Mn（Ⅲ） might play and its environmental impact.In this paper we conducted experiments to discuss the ideal reaction condition and give out evidence that strongly implicates Mn（Ⅲ） in the oxidation of Cr（Ⅲ） by birnessite synthesized at high pH.1、Mn（Ⅲ） affected the oxidation fate of Cr（Ⅲ） in a distinct way,and the leading part of it was not that remanined in the birnessite,but that presented after Mn（Ⅳ）→Mn（Ⅲ） electron transforming.It is also acceptable to conclude that the rate of reaction could be limited by the step of electron transform from Mn（Ⅳ） to Mn（Ⅲ）.2、The birnessites which had been treated with Na₄P₂O₇ would provide more adsorbable sites for Cr（Ⅲ）,and there was only Mn（Ⅳ） took part in the oxidation once Mn（Ⅲ） appeared during the reaction was complexed by Na₄P₂O₇ in solution.Meanwhile,the Mn realease amount demonstrated that Na₄P₂O₇ in solution could inhibit the electron transform from Mn（Ⅲ） to Mn（Ⅱ）,but it also promoted the electron transformation process of Mn（Ⅳ）→Mn（Ⅲ）. 3、The two reaction pathways used to discuss the initial K_obs,the first of these pathways was postulated to be sensitive to Mn（Ⅲ）concentration,but the second one was thought to be independent of Mn（Ⅲ）.The discussion indicated that the later one has less efficiency on reaction rate of Cr（Ⅲ） than the former one.This is the further evidence to testify Mn（Ⅳ） just has the greater oxidation capacity in thermodynamic equilibrium,but not for the oxidation rate in dynamic process.更多还原