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

The effects of urotropin on the hydrolysis of Fe(3+) ions in NH(4)Fe(SO(4))(2) solutions at 90 degrees C were investigated using X-ray powder diffraction, (57)Fe Mossbauer spectroscopy, Fourier transform infrared spectroscopy, and transmission electron microscopy. Three concentrations of NH(4)Fe(SO(4))(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 Fe(3+) hydrolysis, samples were dominantly amorphous, alpha-FeOOH, alpha-Fe(2)O(3) and NH(4)Fe(3)(OH)(6)(SO(4))(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 proven in the precipitates. It was suggested that the particles of amorphous fraction, as well as alpha-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. Mossbauer spectroscopy indicated superparamagnetic behavior of alpha-FeOOH particles. Formation of alpha-FeOOH. particles of colloidal dimensions was proven by transmission electron microscopy.