maghemite

A maghemita é um mineral formado a partir da oxidação da magnetita em baixas temperaturas, um composto intermediário da oxidação magnetita-hematita. A maghemita pode ser erroneamente identificada como magnetita por difração de raios X e/ou como hematita por análise química pontual em MEV. No entanto, a magnetita não-estequiométrica foi detectada e quantificada em amostras de solos e de minérios de ferro brasileiros pelo refinamento de sua estrutura com o método de Rietveld. Os resultados foram confirmados por microscopia ótica e espectroscopia Raman, validando o método. A difração de raios X com o refinamento da substituição isomórfica de Fe 2+ por Fe 3+ ao longo da solução sólida magnetita-maghemita pode ajudar a caracterizar adequadamente a maghemita em minérios de ferro.
 
Maghemite is a mineral formed from magnetite oxidation at low temperatures, an intermediate term of the magnetite-hematite series. Maghemite could be misidentified as magnetite by X-ray diffraction, and/or as hematite by spot chemical analysis. Nevertheless, non-stoichiometric magnetite was detected and quantified in samples of Brazilian soils and iron ores by the Rietveld method refinement of its structure. The results were confirmed by optical microscopy and Raman spectroscopy, thus validating the method. X-ray diffraction with the refinement of the isomorphic substitution of Fe 2+ by Fe 3+ along the magnetite-maghemite solid solution could help to suitably characterize maghemite in iron ores.

In this study, a nano-layer polydopamine (PDA) coated superparamagnetic maghemite nanoparticles (MNPs) was applied to investigate the asphaltene adsorption-desorption behavior using a model solution. In this process, Fouriertransform infrared spectrum (FT-IR) spectroscopy of the polydopamine/MNP core/shell (MNP@PDA) before and after asphaltene adsorption was indicated the attachment of asphaltene molecules on the polymeric nano-adsorbent surface. The isotherms and kinetics of the asphaltene adsorption process on the MNP@PDA were studied. The good prediction of asphaltene adsorption by the modified Langmuir model indicated that adsorption occurs on an MNP@PDA surface by multilayer adsorption. Also, within the kinetic models, the double-exponential model can fit the experimental data well. The obtained results revealed that about 90% removal for asphaltene happened within 30 min which can be acceptable. The results of this study showed that natural polymers can be used for surface modification of nanoparticles and use it successfully for asphaltene adsorption from prepared asphaltene-toluene solution.

Maghemite nano-particles were synthesized by a solid-state chemical reaction for its highly selective use as, cyclotron-produced, 109Cd (462.9 days) purification method of choice. 109Cd radiochemical separation starts with Ag activities precipitated with HCl 0.0015 M followed by, on a second step, 109Cd separation from Cu carrier and 65Zn (243.8 days) using Ca (NO3)2 0.01 M. Experimental parameters such, pH and sorbent concentration, on 109Cd