The reduction of chromate ions by Fe(II) layered hydroxides

International audienceThe reduction of chromate ions by Fe(OH)2 and the iron (II)-iron (III) hydroxysulphate green rust, GR(SO42-), was studied to evaluate whether such synthetic layered hydroxides and the corresponding natural green rust mineral could be involved in the natural attenuation of contaminated environments. The resulting Cr (III) bearing phases, which would govern the subsequent behaviour of chromium, were clearly characterised. Both compounds proved to be very reactive and oxidised instantaneously while chromate ions were reduced to Cr (III) as evidenced by X-ray photoelectron spectroscopy. Mass balance (ICP-AES) demonstrated that the Fe/Cr ratio inside the solid end product was equal to the initial Fe/Cr ratio. The solid phases, analysed by X-ray diffraction, Raman and Mossbauer spectroscopies were identified as Cr-substituted poorly crystallised iron (III) oxyhydroxides in both cases, more precisely d-FeOOH when starting with Fe(OH)2 and ferrihydrite when starting with GR(SO42-)

Role of Al(III) and Cr(III) on the formation and oxidation of the Fe(II-III) hydroxysulfate Green Rust

International audienc

Oxidation of chukanovite (Fe 2 (OH) 2 CO 3 ): Influence of the concentration ratios of reactants

International audienc

Corrosion and cathodic protection of carbon steel in the tidal zone: Products, mechanisms and kinetics

International audienc

Localized corrosion of carbon steel in marine media: Galvanic coupling and heterogeneity of the corrosion product layer

International audienc

Influence of soil moisture on the residual corrosion rates of buried carbon steel structures under cathodic protection

International audienc

Nickel incorporation in Fe(II, III) hydroxysulfate Green Rust: effect on crystal lattice spacing and oxidation products Incorporação de níquel em Fe (II-III) Grenn Rust hidroxisulfato: efeito sobre a estrutura cristalina e produtos de oxidação

Ni(II)-Fe(II)-Fe(III) layered double hydroxides (LDH) or Ni-containing sulfate green rust (GR2) samples were prepared from Ni(II), Fe(II) and Fe(III) sulfate salts and analyzed with X ray diffraction. Nickel is readily incorporated in the GR2 structure and forms a solid solution between GR2 and a Ni(II)-Fe(III) LDH. There is a correlation between the unit cell a-value and the fraction of Ni(II) incorporated into the Ni(II)-GR2 structure. Since there is strong evidence that the divalent/trivalent cation ratio in GR2 is fixed at 2, it is possible in principle to determine the extent of divalent cation substitution for Fe(II) in GR2 from the unit cell a-value. Oxidation forms a mixture of minerals but the LDH structure is retained if at least 20 % of the divalent cations in the initial solution are Ni(II). It appears that Ni(II) is incorporated in a stable LDH structure. This may be important for two reasons, first for understanding the formation of LDHs, which are anion exchangers, in the natural environment. Secondly, this is important for understanding the fate of transition metals in the environment, particularly in the presence of reduced Fe compounds.<br>Amostras de hidróxidos de dupla camada (HDC), ou "sulfate green rust" (GR2), contendo Ni foram preparadas utilizando-se sulfatos de Ni(II), Fe(II) e Fe(III) e analisadas por difração de raios X. O Ni está incorporado na estrutura do GR2 e forma um sólido entre GR2 e um HDC contendo Ni(II)-Fe(III). Há correlação entre os valores de "a" da célula unitária e os da fração de Ni(II) incorporado na estrutura do Ni(II)-GR2. Desde que haja forte evidência de que a razão entre os cátions divalente/trivalente no GR2 seja igual a 2, é possível, a princípio, determinar a extensão da substituição do cátion divalente por Fe(II) no GR2 a partir dos valores de "a" da célula unitária do cristal. Sob o efeito da oxidação, é formada uma mistura de minerais, porém a estrutura do HDC não é alterada se pelo menos 20 % dos cátions divalentes na solução inicial forem de Ni(II). Isso parece indicar que o Ni(II) está incorporado à estrutura estável do HDC, o que é importante por duas razões: para entender a formação dos HDC, os quais são trocadores aniônicos em condições naturais no meio ambiente; e para entender o destino dos metais de transição no ambiente, particularmente na presença de compostos de Fe na forma reduzida