Influence of Sulfate Ions on Conversion of Fe(OH)<SUB>3</SUB> Gel to β-FeOOH and α-Fe<SUB>2</SUB>O<SUB>3</SUB>

Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analyses were used for characterizing the effect of sulfate ions on the conversion rate of condensed Fe(OH)3 gel, prepared from FeCl3 and NaOH solution, to β-FeOOH and α-Fe2O3 particles by aging at 100°C. Fine particles and supernatant solution were sampled from the aged suspensions containing colloidal particles. XRD profiles and TEM observation showed that β-FeOOH was formed from the gel and subsequently converted into α-Fe2O3. It was revealed that the addition of sulfate ions accelerated the β-FeOOH formation from the gel, but delayed the conversion from β-FeOOH to α-Fe2O3. The concentration changes of sulfate and chloride ions in the supernatant solution phases were in agreement with the conversion from Fe(OH)3 gel to β-FeOOH and α-Fe2O3 particles.