Influence of Urotropin on the Precipitation of Iron Oxides from FeCl3 Solutions

Precipitations of iron oxides from FeCl3 solutions in the presence of urotropin at 90 oC were monitored using the Fourier transform infrared spectroscopy, Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy. Urotropin was used as a generator of OH– ions. The precipitation processes depended on the concentrations of FeCl3 and urotropin and the time of aging. After 1 day of aging the precipitation systems up to pH 2, the -FeOOH phase was precipitated, while in the region of 5 < pH < 6 the mixtures of -FeOOH, -Fe2O3 and -FeOOH were precipitated, and at pH > 6 the mixtures of -Fe2O3 and -FeOOH were observed. The -FeOOH phase precipitated at 2.16 < pH < 5.55 dissolved after 7 days, yielding soluble iron for the -FeOOH growth on account of -Fe2O3. At pH 1.5 and less, -FeOOH was present as a single phase up to 7 days of aging the precipitation systems. The mechanisms of iron oxide precipitation in dependence on pH were discussed. The size and morphology of oxide particles were strongly influenced by experimental conditions of the precipitation process as shown by transmission electron microscopy. CROATICA CHEMICA ACTA CCACAA 71 (4) 1019¿1038 (1998)