Formation of Iron(III) Hydroxide Particles from Iron(III) Salt Solutions by Homogeneous Precipitation Method

Abstract

Homogeneous precipitation method using urea was applied at 65-95°C for the formation of iron(III) compounds particles from aqueous solutions of FeCl₃, Fe(NO₃)₃ and Fe(NH₄)(SO₄)₂. Precipitate formed was a mixture of α-FeO(OH), /β-FeO(OH) and α-Fe₂O₃ from FeCl₃, while single phase precipitate of β-FeO(OH) was obtained at high concentration of urea. Precipitation from Fe(NO₃)3 solutions resulted in a mixture of α-FeO(OH), α-Fe₂O₃ and γ-FeO(OH), whereas that from Fe(NH₄) (SO₄)₂ resulted in Fe(O₂)₂(NH₄)(OH)₆(SO₄)₂ and α-FeO(OH). Precipitate of Fe3(NH₄)(OH)₆(SO₄)₂was obtained as a single phase only when the degree of precipitation was below -70%. Particles ofβ-FeO(OH) produced from FeCl₃was in spindle or rod-like shape. The particle size increased with decrease in urea concentration, with decrease in reaction temperature and with increase in FeCl₃ concentration. The aspect ratio of β-FeO(OH) particles increased as they grew in size.