Synthesis and Characterization of Magnesium Magnetites and Their Weathering Products.

The iron oxides and hydroxides nanoparticles are important minerals due to numerous applications, and their abundance in soils of tropical and sub-tropical regions in Brazil. Magnesioferrite or magnesium magnetites (Fe3-x Mgx O4) were identified as precursor of maghemites and hematite in the process of weathering. This study aimed to synthesize magnetite and magnesium magnetites using magnesium sulphate in molar fractions ranging from 0.00 mol% of magnesium to 33.0 mol% in the presence of potassium hydroxide and potassium nitrate. The methodology consisted of dissolving ferrous sulfate in deionized water prior to N2 flow in a glass bottle covered with plastic film, where were also inserted a thermometer and a funnel feeder. The system was heated to 90oC and stirred with a magnetic stirrer. The production of iron oxides with varying degrees of Mg for Fe isomorphic substitution was performed by adding soluble magnesium salt to facilitate formation of the respective material. The following proportions of Mg for Fe isomorphous substitution was tentatively produced : 0.00, 1.25, 2.50, 3.75, 5.00, 10.00, 20.00, 30.00, 33.00 mol%. After the synthesis the solid products were washed with deionized water to remove excess salts, frozen in liquid nitrogen and lyophilized. The powder material was characterized by standard methods in their chemical, physical and mineralogical attributes. Total chemical analysis showed that the proportions of x in the nominal chemical formula Fe3-x Mgx O4 were: 0.00, 0.038, 0.076, 0.11, 0.15, 0.23, 0.30, 0.45, 0.60, 0.90, 1). X-rays diffraction data showed the presence of other minerals and their increasing content was proportional to the amount of magnesium sulphate added. The other minerals were precipitated arcanita, and an unprecedented yavapaiita and muskoxita, coexisting with magnesian magnetite. The muskoxita was formed from the increasing concentrations of iron and magnesium to have greater solubility than the magnesioferrite, magnesioferrite by competing with iron and magnesium in solution. Mehlich 1 dissolution procedure and the seeding of the minerals in wet soil removed all minerals but the magnetite.