高铁酸盐的稳定性与Fe(VI)向Fe(IV)转化反应的研究

【作者】 李国亭；

【导师】 贾汉东；

【作者基本信息】 郑州大学 ， 无机化学， 2003， 硕士

【摘要】 水问题是21世纪的核心科学问题之一。高铁酸盐具有极强的氧化性和优良的絮凝功能，是一种优良的水处理剂，正是由于高铁酸盐在水处理方面的优异性能才使它获得了前所未有的发展前景。但是，高铁酸盐有自催化现象，具有不稳定性，不能够象液氯一样长期保存，这大大限制了它的大规模应用。为了找到稳定高铁酸盐的方法，拓展其应用前景，我们进行了一系列研究。 碱性溶液中高铁酸盐有两种分解途径，一种是快反应（1），另一种是较慢的反应（2）：4FeO₄^2-+10H₂O=4Fe（OH）₃+8OH^-+3O₂↑ （1） 2FeO₄^2-=2FeO₃^2-+O2↑ （2） 反应（1）是公认的造成高铁酸盐溶液不稳定的本源反应，反应（2）则是新发现的一个由Fe（Ⅵ）的紫色溶液变成Fe（Ⅳ）绿色溶液的副反应。本论文以这两个化学反应作为研究对象，进行了两方面的研究工作：第一方面是为了减缓或阻止反应（1）的进行，找到使高铁酸盐溶液稳定的方法，而进行的搀杂对高铁酸盐溶液稳定性影响的研究；另一方面是围绕反应（2）而展开的探索，即关于Fe（Ⅳ）本身及Fe（Ⅵ）向Fe（Ⅳ）转化反应的研究。这两方面的研究工作，均得到一些有益的、新颖的结果。 通过研究不同浓度的NaOH和KOH碱液及不同的阴阳离子对于高铁酸盐的稳定作用，得出以下结论： 1．对于相同的碱度，用NaOH作碱介质比用KOH作碱介质更能使高铁酸盐稳定，稳定效果更明显，实验时宜选用NaOH作碱介质。同时，在NaOH作碱介质时，以6mol／l及以上浓度的NaOH溶液对高铁酸盐的稳定作用最为突出。 2．对阴离子掺杂试验，无论在含ClO^-与不含ClO^-的高铁酸盐溶液中，当掺杂物质为NaIO₄时稳定作用十分明显，其次为Na₂SiO₃、KBr、Na₃PO₄，再次为KBrO₃、Na₂B₄O₇。当掺杂物质为KI、KIO₃时，高铁酸盐溶液一经振荡即迅速分解完毕。总体上而言，随着掺杂物质如Na₂SiO₃，Na₂C₂O₄、Na₃PO₄掺杂量的增加，阴离子对高铁酸盐呈现出逐步增强的稳定作用。 3．对阳离子掺杂试验，当掺杂物质为Pb（NO₃）₂、SnCl₂、Cr（NO₃）₃、HgCl₂时，高铁酸盐溶液（无论是含次氯酸根的高铁酸盐溶液与不含次氯酸根的高铁酸盐溶液）一经振荡高铁酸盐即迅速分解完毕。当掺杂物质为CoCl₂、NiCl₂、CuCl₂加入时，振荡后高铁酸盐溶液紫色变浅，而且一天内紫色即完全消失。阳离子掺杂均未表现出对高铁酸盐的稳定作用。 4.掺杂的稳定作用的机理有两种解释:热力学机制，NaCIO具有较强的氧化性，对Fe伽“一有极强的稳定作用，NalO;稳定作用的机理和Naclo相似。配位机制，re（oH）:与e2042一，Po4，一配位而生成Fe（eZo4）33一等配离子，这些配离子并不会催化分解Feo42一。 接着研究了Fe（IV）的定性鉴定及稳定性机理。我们采用多种鉴定方法，如红外光谱和紫外可见光谱法，氧化性实验等确认Fe(vD降解而得到的绿色溶液为Fe（IV）化合物溶液。Fe(IID对Fe04“一碱性溶液中的分解反应有强烈的催化作用，从而造成Feo42一难于稳定，而Fe(IID对Fe（Iv）绿色碱性溶液无催化作用，这是FeW能稳定存在的重要动力学原因。 为了便于展开Fe（W）的各方面研究，我们建立了Fe（W）的直接分光光度测定法。通过实验得到A一C线性回归方程:eFelv=K。+KIA，Ko=3.955 x 10一smol月，K，一4.620 xlo一4mol/1，相关系数R=0.9997。与经典的邻二氮菲测铁法对照，直接分光光度法测定Fe（Iv）是准确可靠的。同时，直接分光光度法测定Fe（Iv）操作简便快速，制备过程中，可能引入体系的K+、Na+、Cl一、Clo--、N仇一等无色杂质离子不干扰测定。但因Fe（IV）只能在高碱度条件下稳定，所以测定时必须使溶液体系保持高碱度。 为了研究Fe(VD向Fe（IV）的转化反应机理，我们建立了高铁酸盐中Fe（IV）和Fe（vl）的同时测定的三波长与双波长分光光度法。三波长与双波长分光光度法对高铁酸盐中Fe（Iv）和Fe（Vl）的同时测定方法中，选定SO7nm、695.8 nm双波长组合波长测定Fe（VI），选定560nm、605 nm、669run三波长组合波长测定Fe（w）。三波长与双波长分光光度法对高铁酸盐中Fe（W）和Fe（VI）的同时测定，准确、可靠，平均回收率为101.%%，便于实际应用。 最后我们研究了Fe（Vl）向Fe（IV）的转化反应。溶液中Fe（Vl）和Fe（IV）的浓度变化呈此消彼长的态势，即随着时间的增加，Fe（VI）的浓度急剧降低，而Fe（lv）的浓度则缓慢增加。当Fe(vD的浓度降低到10一sm。1/’1数量级时，若此时溶液呈现绿色（可用肉眼辨别），则Fe（w）的浓度也己经缓慢增加到了10一5m。l/1数量级左右。CIO一的存在不对Fe（IV）的生成产生根本性的影响。在溶液中Fe（VI）向Fe（W）转化的同时，Fe（Vl）大部分转化成了Fe（OH）3，生成Fe（IV）的量远小于F。（Vl）的起始量，而且Fe（OH）3存在量的大小不会对Fe（IV）的生成构成明显影响，只会加速Fe（Vl）的分解。只要不会使Fe（vl）迅速分解，碱度对Fe（vl）向Fe（Iv）的转化速率影响不大。 由以上结论知，强碱性溶液中高铁酸盐Fe（vI）自身只可能有两种转换途径，转化为能够长期稳定的Fe（Iv）或直接转化为Fe（ oH）:。要使高铁酸盐Fe（vl）稳定，除了增加CIO一?更多还原

【Abstract】 The problem of water is one of the nuclear problems of science in 21st century. Ferrate(VI) is a strong and environmentally friendly oxidant, coagulant, and water treatment agent, which lead to its unprecedented future practical application in many fields. But ferrate(VI) has the property of self-catalysis, unlike the stability of chlorine, which contributes to its low stability in solution and prohibits its wide use. In order to find a solution to this problem and enlarge its scope of use, a series of study is carried out on it.In basic solution, there are two approaches to the decomposition of ferrate(VI),one of which is a quick reaction(l)and the other a slow reaction(2).4FeO42- + 10H2O = 4Fe(OH)3 + 3O2 t +8OH- (1)2FeO42- =2 FeO32-+ O2 t (2)Reaction(l) is a fundamental reaction leading to its low stability, which has gained its public recognition, but reaction(2) is a newly-found side reaction which describes Fe(VI) degenerating into Fe(IV).In studying the two reactions, we develop the work in two aspects. Firstly, in order to delay or stop reaction(l)and find a solution to its low stability, we study the effect of doped ions on ferrate(VI). Secondly, centered on reaction(2), we study ferrate(IV) itself and the reaction .Through the work referred before we come up with some beneficial and new conclusions.Through studying the effect of KOH and NaOH with different concentrations on ferrate(VI) and the stabilizing effect of doped ions on ferrate(VI), we conclude:1. With the same alkalinity, NaOH has a longer stabilizing effect on ferrate(VI) than KOH and with the effect it is wise to choose NaOH as the medium for the experiment. At the same time, when NaOH as the basic medium, basic solution of 6mol/l or higher concentration plays a very outstanding stabilizing effect on ferrate(VI).2. When doped with substances which are used to test their anions’ stabilizing effect on ferrate(VI), whether in solutions with ClO- or without ClO-, NaIO4 shows its excellent stabilizing effect(the best) and the following substances (with different anions) are Na2SiO3 , KBr, Na3PO4, KBrO3, Na2B4O7., When the doped substances are KK KIO3, ferrate(VI) in basic solution decomposes completely at once. Totally, some anions show their ever-increasing stabilizing effect on ferrate(VI) when the amount of doped anions increases.3. When the doped substances (with different cations) are Pb(NO3)2, SnCl2, Cr(NO3)2x HgCl2, ferrate(VI) in basic solution decomposes completely at once too, whether in solutions with ClO- or without ClO-. When the doped substances are CoCl2,NiCl2, CuCl2, the color of ferrate(VI) solution begins to turn light, till the color of purple disappear in a day. All the doped cations have not showed their stabilizing effect on ferrate(VI).4. In order to explain the mechanism of stabilizing effect of doped ions, we forward these two principles: First, the principle of thermodynamics. NaCIO has a very strong redox potential through the entire pH range and plays a very strong stabilizing effect ferrate(VI). NaIO4 conforms to the same principle. Second, the principle ofcoordination. Fe(OH)3 coordinates with such ions as C2O42-, PO43-, which produces coordination ions Fe( C2O4)33- and so on, and these coordination ions do not catalyze the decomposition of FeO42-.Then characteristic identification and stabilizing mechanism are studied. Using such identification as IR, U-V spectrum and the tests of oxidation the solution which is transformed from ferrate(VI) decomposition is identified as ferrate(IV). ferrate(III) can catalyze the decomposition of FeO42~ greatly, which leads to the low stability of ferrate(VI), but at the same time ferrate(HI) can not catalyze the decomposition of ferrate(IV), which explains the dynamic reason why ferrate(IV) is stable in solution with ferrate(IH).In order to enhance the further study on ferrate(IV), direct spectrophotometer determination is established. Through the study we get a linear equation: CFeiv=K0+K1A, K(r=3.955X10~8mol/L K1=4.620X更多还原