Mecanismos químicos e mineralógicos de transformação da magnesioferrita de solo derivado de tufito, da região do Alto Paranaíba, MG

Abstract

Recebido em 13/11/08; aceito em 3/4/09; publicado na web em 26/8/09 CHEMICAL AND MINERALOGICAL MECHANISMS RELATED TO THE TRANSFORMATION OF MAGNESIOFERRITE, IN A SOIL FORMING ON TUFFITE IN ALTO PARANAÍBA, MG. Magnetic soils forming on tuffite of the region of Alto Paranaíba, Minas Gerais, Brazil, usually contain iron-rich spinels exceptionally rich in magnesium and titanium. In this work, samples of the magnetically separated portion from the sand fraction of a Brunizém (Chernossolo) and from its mother-rock material were analyzed with synchrotron X-ray diffraction and 57 Fe-Mössbauer spectroscopy. Magnesioferite (MgFe 2 O 4 ) and maghemite (its pure nonstoichiometric spinel structure, Fe 8/3 ⊕ 1/3 O 4 , where ⊕ = cation vacancy, corresponds to γFe 2 O 3 ) were the magnetic iron oxides so identified. Basing on these data, a consistent chemical-mineralogical model is proposed for the main transformation steps involving these iron oxides in the pedosystem, starting on magnesioferrite to finally render hematite (aFe 2 O 3 ), passing through maghemite as an intermediate specie.

Magnetic Properties of Iron Sand from the Tor River Estuary, Sarmi, Papua

“…Although many synthesis approaches have been developed, the natural magnesioferrite (MgFe 2 O 4 ) mineral has rarely been found. To the best of the author's knowledge, it has been identified in soils from the Alto Paranaíba region, State of Minas Gerais, Brazil [26,27] and in Victorian Brown Coal Fly Ash from the Latrobe Valley, Australia [28]. Magnesioferrite is known to be an important magnetic oxide with a spinel structure, with a widespread application in microwave devices due to their low magnetic, dielectric losses and high resistivity.…”

Development of an Electrochemical Sensor Based on Nanocomposite of Fe3O4@SiO2 and Multiwalled Carbon Nanotubes for Determination of Tetracycline in Real Samples

“…In the Fe 3 O 4 @SiO 2 spectra, the bands at around 570 cm −1 and 449 cm −1 can be assigned to the stretching and angular deformation of the Fe-O bond in the magnetic core, respectively. The x-ray diffractogram (Figure 3B) of the Fe3O4@SiO2 nanoparticles revealed welldefined peaks located around 2θ = 30.4°, 36.02°; 43.6°; 53.8°; 57.4°; 62.9°, characteristics of the crystalline planes (220), ( 311), ( 101), ( 422), (511), and (440), respectively, of the cubic structure of magnetite [33], according to JCPDS number 36-0398 [34].…”

“…The X-ray diffractogram (Figure 3B) of the Fe 3 O 4 @SiO 2 nanoparticles revealed welldefined peaks located around 2θ = 30.4 • , 36.02 • ; 43.6 • ; 53.8 • ; 57.4 • ; 62.9 • , characteristics of the crystalline planes (220), (311), ( 101), ( 422), (511), and (440), respectively, of the cubic structure of magnetite [33], according to JCPDS number 36-0398 [34].…”