The effect of experimental conditions on the microstructure of hematite particles precipitated by the forced hydrolysis of FeCl3 solutions

The effect of experimental conditions on the forced hydrolysis of FeCl3 solutions and specifically the effect of amidosulphonic acid on the microstructure of precipitates were investigated. Precipitates were analyzed by XRD, 57Fe Mössbauer, FT-IR and UV/Vis/NIR spectroscopies, as well as FE-SEM. The phase transformation β-FeOOH → α-Fe2O3 was accelerated with an increase in the hydrolysis temperature, whereas an addition of amidosulphonic acid at the start of the hydrolysis of Fe3+ ions suppressed the phase transformation β-FeOOH → α-Fe2O3 or decreased crystallinity at 120 and 160 °C. The size and shape of hematite particles were strongly dependent on FeCl3 concentration and temperature and the presence of sulfonate/sulfate groups. Preferential adsorption of sulfonate/sulfate groups influenced the hematite crystal growth direction. The aggregation effect was also noticed in the formation of hematite particles.

• The effect of experimental factors on the forced hydrolysis of FeCl3 solutions were investigated.
• The presence of amidosulfonic acid influenced the α-Fe2O3 microstructure.
• Aggregation plays an important role in the formation of α-Fe2O3 particles.
• The sulfonate/sulfate groups directed the growth of α-Fe2O3 subcrystals.