Iron oxides are common minerals that occur in the environment, either naturally or as a result of human activities.The most common Fe(III)-hydroxides and -oxides include ferrihydrite (Fe5HO8 .4H2O) that transforms to hematite (a-Fe2O3 ) and/or goethite (a-FeOOH).That depends on the solution composition, temperature and pH. Depending on the composition of the solid and solution, oxidation can transform the green rust (a product formed by a metal corrosion) to lepidocrocite (γ -FeOOH) or magnetite (Fe(II)Fe(III) 2O4 ). Weathering can degrade magnetite to maghemite (γ –Fe2O3 ) and all of the Fe-oxides are subject to an attack and dissolution by organic acids and ligands that are formed during the breakdown of biological material. Iron oxides can be prepared by hydrolysis of acidic Fe3+ solutions or by controlled oxidation of Fe2+ solutions. Goethite, lepidocrocite and magnetite were prepared by oxidation of Fe2+ solutions under slightly different values of pH, Fe concentrations and rates of oxidation. Maghemite was prepared by a thermal transformation from synthetic lepidocrocite heated in a furnace at 250 °C for 2h. Hematite was prepared by forced hydrolysis of Fe3+ solution from a chlorine system (FeCl3) at the temperature close to 100 °C under strongly acidic conditions (pH 1-2). Main mineral phases were confirmed by the RTG diffraction and IR spectroscopy method. Iron oxides are excellent, renewable adsorbents, and often control free metals through adsorption reaction
