Nanocomposites and nanomaterials

Transformation of natural hematite into magnetite in aqueous Fe+2-containing medium under the influence of microwave radiation
T.S. Antonenko1, O.Yu. Tsymbal2, N.O. Dudchenko1, A.B. Brik1
1 M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of Ukraine Natl. Acad. of Sci. of Ukraine, Palladina prosp, 34, Kiev-03680, Ukraine. 
E-mail: tetyana_savchenko@ukr.net
2 Institute of Geology, T. Shevchenko’s National University, Vasylkivska, 94, Kiev, Ukraine 

Nowadays, resources of high-grade iron ores and easily enrichable iron ores (e.g. magnetite quartzite) are almost exhausted. That's why there is an increasing necessity of iron ore concentrates production from low-grade oxidized iron ores (e.g. hematite quartzite) and from iron-processing gangue (e.g. tailings). 
The aim of this work was to investigate phase transformations of hematite, contained in the oxidized iron ore from Kryvyy Rih basin, into magnetite in aqueous Fe+2-containing medium under the influence of microwave radiation.
Samples of natural hematite was obtained by grinding of hematite ore from Kryvyi Rih region up to <70 mkm. The phase composition of initial sample of hematite ore was mainly hematite with quartz traces. Saturation magnetization of initial sample was < 1 Am2/kg.
For phase transformation carrying-out, 5 ml of 10% solution of ferrous sulfate were added to 1 g of initial sample. After that, the reaction was started by adding of 24 ml of 3M ammonia. The pH of solution was ~12. Then the solution was incubated in microwave device (Anton Paar Multiwave PRO) at T = 250°C and increased pressure for 30 min.
The result of XRD-measurements shows that after phase transformation of hematite ore the new phase of magnetite appears. Characteristic peaks at XRD pattern of obtained samples after transformation (4,84Å, 2,97Å, 2,53Å, 2,10Å, 1,61Å, 1,48Å) were attributed to magnetite. The saturation magnetization of all obtained sample after transformation increases up to 32 A∙m2/kg. It was shown, that saturation magnetization decreases with increasing of samples’ grain size.
We could conclude that transformation of hematite in Fe2+-containing solution under the influence of microwave radiation leads to phase transformations of weakly magnetic sample and formation of strongly magnetic minerals. The magnetization of obtained samples is rather high and makes them promising for different medical-biological applications.