Nanocomposites and nanomaterials

Phase transformation of synthetic nanosized goethite by reducing with carbohydrates
N.O. Dudchenko1, T.S. Antonenko1, 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

Ukraine has significant resources of weathered iron ores and iron-containing waste, containing highly dispersed iron oxides and hydroxides. Such wastes occupying large areas and polluting mining regions should be processed. One of the ways of processing is to transform weakly magnetic minerals into highly magnetic minerals with its further beneficiation using magnetic separation.
The aim of this work was to create synthetic goethite nanoparticles and investigate their transformation by reducing with starch. Synthetic goethite was created as follows: a solution of 0,48M sodium hydrogen carbonate (50 ml) is slowly poured under intensive stirring into the solution of 0,4M iron (III) nitrate (50 ml), and then the resulting suspension was heated up to boiling and then cooled down. After, solution of 5M sodium hydroxide in 100ml of distilled water was added into suspension. The formed precipitate is left in the thermostat for 24 hours at a temperature of 90 °C. During this time, the precipitate is completely turned into crystalline light-yellow goethite. According to data of the XRD data, the sample is represented only by a phase of goethite without any admixtures. Phase transformations were performed using a custom-built facility that enables automatic registration of sample magnetization with the temperature. Reduction of goethite with starch was performed under heating up to 600 °C.
It was shown that the sample has a temperature of 260°C for the beginning of the reaction and 465°C for its maximum rate. The saturation magnetization of sample increases strongly, indicating the arising of the phase of magnetically ordered material. The Curie temperature of the obtained product was 564°C, which are close to the Curie temperature of magnetite (580°C). The saturation magnetization of obtained sample was 70 A∙m2/kg. According to XRD data, the peaks of goethite disappear and peaks of magnetite arise.
We could conclude that heat treatment of the synthetic goethite at the temperatures up to 600°C in the presence of starch leads to phase transformations of weakly magnetic sample and formation of strongly magnetic minerals.