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Hydroxysulfate Green Rust GR(SO4 2–) or sulfate fougerite is the typical member of the layered double hydroxide (LDH) family and plays an important role in the global biogeochemical cycle of iron and concomitant elements. The sulfatebearing Green Rust is developed in the following environmental systems: mid-ocean ridge hydrothermal vents, volcanic systems, marine sedimentsand hydromorphic soils. Usually its formation in the nature is realized in seawater under corrosion processes. Due to high reductive properties and chemical activity of natural Green Rusts their study is highly complicated; consequently Green Rust formed under laboratory conditions is often used for modeling natural processes of mineral formation. The surface of iron alloys may be one of the suitable systems for the research of Green Rust development. So, we studied the development and phase transformation of the hydroxysulfate Green Rust on the surface of the steel 3 contacting with ferric and ferrous sulfate water solutions under oxidative and reductive conditions. The concentration of dissolved ferric and ferrous iron was chosen as 10, 100 and 1000 mg/dm3. The pH values were set at 3.5 and 6.5. The X-ray diffraction in situ was used as the main method of the research. The measurement was taken by the computer-aided equipment (DRON 3) supplied with two Seller slits and filtered emission of cobalt anode. The critical Woolf-Bragg angle was determined at around 80 °C. The XRD study permitted to see the processes of the development of the nanosized iron-oxygen minerals on the steel surface within 72—90 h. Scanning electron microscopy using JOEL-6700 microscope equipped by energy-dispersive and cathode-luminescence attachment was chosen as a visualization technique for description of the particle morphology. The structures of hydroxysulfate Green Rust, lepidocrocite and goethite belong to the main mineral phases formed on the steel surface under the RCD conditions. Magnetite particles appear on the steel surface when it contacts with low concentration of ferrous iron solutions in the wide range of pH. The simultaneous presence of schwertmannite, ferrihydrite and Fe(III)–Green Rust that are the components of the phase transformation chains points to the continuity of the phase formation process. The heterogeneity of the steel surface and presence of anodal and cathodal areas together with structural defects are found as other reason for the variety of mineral composition. The following chains of phase the transformation on the steel surface contacting with ferric and ferrous water solution are supposed: 1) schwertmannite → ferrihydrite) or goethite → Green Rust via dissolution-precipitation process in the corrosion pittings (anodal areas); 2) Green Rust → Fe(III)–GR and/or lepidocrocite via solid state transformation (cato dal areas); 3) dissolved Green Rust or ferric and ferrous micellar species → magnetite under reductive conditions; 4) magnetite → lepidocrocite or goethite under oxidative conditions; 5) Green Rust → lepidocrocite in acid medium and 6) ferric and ferrous micellar species → nanomagnetite in alkaline medium.*

Development of the Hydroxysulfate Green Rust on the Steel Surface Contacting with Water Ferric and Ferrous Salt Solutions