The mechanisms of oxidation of ferrous hydroxychloride beta-Fe-2(OH)(3)Cl in aqueous solution: The formation of akaganeite vs goethite
The mechanisms of oxidation of ferrous hydroxychloride beta-Fe-2(OH)(3)Cl in aqueous solution: The formation of akaganeite vs goethite
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DOI：
10.1016/s0010-938x(97)86102-1
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发表时间：
1997-03-01
影响因子：
8.3
通讯作者：
Genin, JMR
中科院分区：
文献类型：
--
作者：
Refait, P;Genin, JMR
β-Fe-2(OH)(3)Cl是通过混合FeCl2沉淀出来的。含有大量过量氯化亚铁的4H(2)O和NaOH水溶液。这个过剩是由反应物初始浓度的实验比率R‘决定的(R’=[Cl-]/[OH-]或2x[FeCl2]。4H(2)O]/[NaOH]，[NaOH]=0.4moll(-1)，变化范围为5~9。无论R‘值如何，β-Fe-2(OH)(3)Cl的氧化首先生成标准的含氯绿色铁锈Gr1(Cl-)，式为[(Fe3FeIII)-Fe-II(OH)(8)](+)[Cl.NH(2)O](-)。然后，由于溶液的氯离子浓度很大(从2moll(-1)到3.6moll(-1))，Gr1(Cl-)的氧化通常导致伽马-FeOOH型纤锌矿，产生一种过氯化的Gr1化合物，Gr1(Cl-)*，其总组成为[(Fe3-xFe1-xIII)-Fe-II(OH)(8)]((1+x)+)[Cl-1+x.(n-y)H2O]((1+x)-).插层氯离子的过剩x随R‘增大，即随着氯离子浓度的增加而增大，最高可达1/3左右。此外，这些过度氯化的GR1(Cl-)*化合物的氧化过程随R’而变化。当R‘小于或等于6.0时，生成α-FeOOH针铁矿，但这种化合物的形成与前体GR1化合物中发生的修饰无关，因为它是由溶解的Fe(II)物种FeCl2aq诱导的。相反，当R‘大于或等于6.5时与针铁矿一起形成的阿卡奈石，以及当R’大于或等于8.0时与针铁矿一起形成的阿卡奈石的形成与GR1(Cl-)*化合物氯含量的增加有关。最后，在Gr1(Cl-)和β-Fe-2(OH)(3)Cl之间的平衡条件下测量电极电位和溶液的pH，可以估算出在Mu(0)[β-Fe-2(OH)(3)Cl]=-219 600cal mol(-1)时的标准化学电势。(C)1997年爱思唯尔科学有限公司。
beta-Fe-2(OH)(3)Cl is precipitated by mixing FeCl2 . 4H(2)O and NaOH aqueous solutions with a large excess of ferrous chloride. This excess is determined by the experimental ratio R' of the initial concentrations of reactants (R'=[Cl-]/[OH-] or 2 x[FeCl2 . 4H(2)O]/[NaOH] with [NaOH]=0.4 moll(-1)) which varies from 5 to 9. Whatever the value of R', the oxidation of beta-Fe-2(OH)(3)Cl first gives rise to the standard chloride-containing green rust one GR1(Cl-) with formula [(Fe3FeIII)-Fe-II(OH)(8)](+)[Cl . nH(2)O](-). Then, due to the large chloride concentration of the solution (from 2moll(-1) to 3.6moll(-1)), the oxidation of GR1(Cl-), which usually leads to gamma-FeOOH lepidocrocite, produces an over-chlorinated GR1 compound, GR1(Cl-)*, with the general composition of [(Fe3-xFe1-xIII)-Fe-II(OH)(8)]((1+x)+)[Cl-1+x.(n-y)H2O]((1+x)-). The excess x of intercalated Cl- ions increases with R', i.e. with the chloride concentration, up to a maximum around 1/3. Moreover, the oxidation process of these over-chlorinated GR1(Cl-)* compounds changes with R'. It produces alpha-FeOOH goethite when R'less than or equal to 6.0 but the formation of this compound is not connected to the modifications occurring in the precursor GR1 compound since it is induced by a dissolved Fe(II) species, the complex FeCl2aq. In contrast, the formation of akaganeite, which is obtained along with goethite when R'greater than or equal to 6.5 and alone when R'greater than or equal to 8.0, is to be correlated to the increase of the chloride-content of the GR1(Cl-)* compound. Finally, the measurements of the electrode potential and pH of the solution at the equilibrium conditions between GR1(Cl-) and beta-Fe-2(OH)(3)Cl allow to estimate the standard chemical potential of the ferrous hydroxychloride at mu(0)[beta-Fe-2(OH)(3)Cl] = - 219 600 cal mol(-1). (C) 1997 Elsevier Science Ltd.