| 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... |
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