The Precipitates from Aqueous Mixed Solution of FeCl₃ and Fe₂(SO₄)₃ by Hydrolysis

Abstract

The aqueous mixed solution of FeCl₃ and Fe₂(SO₄)₃ has been hydrolyzed at various pH (1.6, 7, and 13), temperatures (30, 50, and 100°C), and mol% of FeCl₃/(FeCl₃+Fe₂(SO₄)₃)(abbr. M. F. ) (0-100%). The precipitates were examined by X-ra y diffraction, electron microscope, DTA, measurements of specific surface area, and chemical analysis. From acidic solution, jarosite, β-FeO(OH), and their mixture were obtained at 100°C under the ce rtain composition of solution (Fig.1). The crystal form of jarosite in the mixture obtained from the mixed solution of 60-75% in M. F. is thinner than that from the mixed solution containing FeCl₃ less than 55% in M. F. (Fig.3). The addition of small amount of Fe₂(SO₄)₃to aqueous FeCl₃ solution (95-85% in M. F. ) made β-FeO(OH) crystals needle sh ape from spindle shape (Fig.3) and reduced content of Cl^- from c. a.15% to 5% in Cl^-/Fe³⁺ m olar ratio (Table 1). The reduction of Cl^--content in β-FeO(OH) crystals led to higher shift of decomposition temperature of β-FeO(OH). The β-FeO(OH) crystals of needle shape was smaller in crystallite size and larger in specific surface area than the β-FeO(OH) crystals of spindle shape. The precipitates from neutral and basic solutions were amorphous hydrous iron oxide and α-FeO(OH), respectively, regardless of the composition of the solutio n and temperature. The effect of coexistence of and SO₄^2- on the hydrolysis of Fe³⁺ was discussed.