engleski

Forced hydrolysis of Fe3+ ions in NH4Fe(SO4)2 solutions containing urotropin

The effects of urotropin on the hydrolysis of Fe3+ ions in NH4Fe(SO4)2 solutions at 90°C were investigated using X-ray powder diffraction, 57Fe Mössbauer spectroscopy and Fourier transform infrared spectroscopy and transmission electron microscopy. Three concentrations of NH4Fe(SO4)2 solutions, 0.03, 0.1 and 0.5 M, with varying initial amounts of urotropin were used in the experiments. Chemical and structural properties of the precipitates strongly depended on the concentrations of the reactants and the time of hydrolysis. In the early stages of Fe3+ hydrolysis, samples were dominantly amorphous. a- FeOOH, a-Fe2O3 and NH4Fe3(OH)6(SO4)2 were crystalline phases detected in the precipitates ; however, the specific phase composition of each precipitate depended on the experimental conditions. The possible formation of schwertmannite was not proved in the precipitates. It was suggested that the particles of amorphous fraction, as well as a-FeOOH particles, contained significant amounts of sulphates on external and internal surfaces due to the specific adsorption. Regularity in the phase composition of the precipitates, as a function of the experimental conditions, was found. Crystallite sizes of oxides were estimated on the basis of the broadening of diffraction lines. Mössbauer spectroscopy indicated superparamagnetic behavior of a-FeOOH particles. Formation of a-FeOOH particles of colloidal dimensions was proved by transmission electron microscopy.

hydrolysis of Fe3+ ; NH4Fe(SO4)2 solutions ; urotropin ; iron-oxides

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