Philippe Refait

Impact of galvanic anode dissolution on metallic trace element concentrations in marine waters

Submerged harbor steel structures often employ cathodic protection using galvanic anodes to guard against corrosion. A laboratory experiment, with three different cathodic protection configurations by galvanic aluminum-based anodes, was performed to evaluate the potential metal transfer from the anodic alloy dissolution into the surrounding marine water. The anode dissolution rate is proportional to the imposed current demands and induced a significant Al, In, and Zn transfer in the dissolved and particulate fractions of the corrosion product layers covering the anode surface. These layers were poorly adherent, even under low hydrodynamic conditions. Consequently, at the anode vicinity, the suspended particle matter and dissolved fraction of surrounding marine waters showed strong enrichments in Al and Zn, respectively, the values of which could potentially affect the adjacent biota. After the anode activation period, however, the metal inputs from galvanic anode dissolution are rapidly diluted by seawater renewal. At regional scale, these metal fluxes should be negligible compared to river and wastewater fluxes. These results also showed that it is difficult to assess the impact of the anode dissolution on the concentrations of metals in the natural environment, especially for metals included in trace amounts in the anode alloy (i.e., Cu, Fe, In, Mn, and Si) in the aquatic compartment.

Effect of orthophosphate on the oxidation products of Fe(II)-Fe(III) hydroxycarbonate: the transformation of green rust to ferrihydrite

Abstract Hydroxycarbonate green rust GR(CO32−) has been synthesized by oxidation of aqueous suspensions of Fe(OH)2 by aeration at the air–liquid interface, in the presence of HCO3− ions at pH 7.5 to 9. During the oxidation of GR(CO32−), ferrihydrite formed first and then turned into goethite by dissolution and precipitation. The oxidation of GR(CO32−) in the presence of orthophosphate ions, which were added as Na2HPO4 · 7H2O salt, also involved the formation of ferrihydrite but not that of goethite, because the dissolution of ferrihydrite is inhibited by the adsorption of phosphate ions on its surface. The oxidation was slowed down because of the suppression of the catalytic effect of iron(III) hydroxide on the oxidation of Fe(II). In anoxic conditions without phosphate, a mixture of GR(CO32−), goethite, and ferrihydrite was observed to transform spontaneously into a mixture of siderite and magnetite. It is thermodynamically consistent, which shows that GR(CO32−) is metastable with respect to the two-phase system FeCO3–Fe3O4. In the presence of phosphate, this transformation was inhibited and GR(CO32−) did not transform in anoxic conditions. Anionic phosphate species dissolved in solution did not give rise to a corresponding GR, i.e., phosphate species did not substitute for carbonate inside the interlayers of the GR. Moreover, iron phosphates did not appear, neither during the oxidation of GR(CO32−) in the presence of oxygen nor in anoxic conditions.

FOUGERITE, A NEW MINERAL OF THE PYROAURITE-IOWAITE GROUP: DESCRIPTION AND CRYSTAL STRUCTURE

Fougerite (IMA 2003-057) is a mixed M(II)-M(III) hydroxysalt of the green rust group, where M(II) can be Fe or Mg, and M(III) is Fe. The general structural formula is:

A solid-solution model for Fe(II)-Fe(III)-Mg(II) green rusts and fougerite and estimation of their gibbs free energies of formation

{[{\rm{Fe}}_{1 - }^{2 + }x{\rm{Fe}}_x^{3 + }{\rm{M}}{{\rm{g}}_y}{({\rm{OH}})_{2 + 2y}}]^{ + x}}{[x{\rm{/}}n{A^{ - n}}.m{{\rm{H}}_2}{\rm{O}}]^{ - x}}

Influence of crucial parameters on the dechlorination treatments of ferrous objects from seawater

[Fe1−2+xFex3+Mgy(OH)2+2y]+x[x/nA−n.mH2O]−x where A is the interlayer anion and n its valency, with 1/4 ≼ x/(1+y) ≼ 1/3 and m ≼ (1−x+y). The structure of green rusts and parent minerals can accommodate a variety of anions, such as OH−, Cl−,

Study of Fe(II) sulphides in waterlogged archaeological wood

{\rm{CO}}_3^{2 - },\;{\rm{SO}}_4^{2 - }

Propriétés de l’interface d’infrastructures métalliques portuaires : facteurs d’impact corrosion/anticorrosion

CO32−,SO42−. The structure of the mineral was studied by Mössbauer, Raman and X-ray absorption spectroscopies (XAS) at the FeK edge. Mössbauer spectra of the mineral obtained at 78 K are best fitted with four doublets: D1 and D2 due to Fe2+ (isomer shift δ ≈ 1.27 and 1.25 mm s−1, quadrupole splitting ΔEQ ≈ 2.86 and 2.48 mm s−1, respectively) and D3 and D4 due to Fe3+ (δ ≈ 0.46 mm s−1, ΔEQ ≈ 0.48 and 0.97 mm s−1, respectively). Microprobe Raman spectra obtained with a laser at 514.53 nm show the characteristic bands of synthetic green rusts at 427 and 518 cm−1. X-ray absorption spectroscopy shows that Mg is present in the mineral in addition to Fe, that the space group is and the lattice parameter a ≈ 0.30–0.32 nm. The mineral forms by partial oxidation and hydrolysis of aqueous Fe2+, to give small crystals (400–500 nm) in the form of hexagonal plates. The mineral is unstable in air and transforms to lepidocrocite or goethite. The name is for the locality of the occurrence, a forested Gleysol near Fougères, Brittany, France. Its characteristic blue-green color (5BG6/1 in the Munsell system) has long been used as a universal criterion in soil classification to identify Gleysols. From a thermodynamic model of soil-solution equilibria, it was proposed that for the eponymous mineral, Fougères-fougerite, OH− may be the interlayer anion. In other environments, the interlayer anion may be different, and other varieties of fougerite may exist. Fougerite plays a key role in the pathways of formation of Fe oxides.

Thermodynamic equilibria in aqueous suspensions of synthetic and natural Fe(II)-Fe(III) green rusts : Occurrences of the mineral in hydromorphic soils

Fe(II)–Fe(III) green rust identified in soil as a natural mineral is responsible for the blue-green color of gley horizons, and exerts the main control on Fe dynamics. A previous EXAFS study of the structure of the mineral confirmed that the mineral belongs to the group of green rusts (GR), but showed that there is a partial substitution of Fe(II) by Mg(II), which leads to the general formula of the mineral:

Trapping of Cr by Formation of Ferrihydrite during the Reduction of Chromate Ions by Fe(II)−Fe(III) Hydroxysalt Green Rusts

{[{\rm{Fe}}_{1 - x}^{2 + }{\rm{Fe}}_x^{3 + }{\rm{M}}{{\rm{g}}_y}{({\rm{OH}})_{2 + 2y}}]^{x + }}{[x{\rm{O}}{{\rm{H}}^ - } \cdot m{{\rm{H}}_2}{\rm{O}}]^{x - }}

Reduction of SeO42- anions and anoxic formation of iron(II)-iron(III) hydroxy-selenate green rust

[Fe1−x2+Fex3+Mgy(OH)2+2y]x+[xOH−⋅mH2O]x−. The regular binary solid-solution model proposed previously must be extended to ternary, with provision for incorporation of Mg in the mineral. Assuming ideal substitution between Mg(II) and Fe(II), the chemical potential of any Fe(II)-Fe(III)-Mg(II) hydroxy-hydroxide is obtained as: