Chemical state analysis of iron (III) compounds precipitated homogeneously from solutions containing urea by means of Mossbauer spectrometry and X-ray diffractometry

Abstract

Chemical states of iron(III) compounds, precipitated homogeneously by heating the iron(III) salt solution at 363 K in the presence of urea, was studied by menas of Mossbauer spectrometry and X-ray diffractometry. The pH-time relation of urea hydrolysis revealed that the precipitation process from homogeneous solution is identical to the hydrolysis of iron(III) ion at pH around 2 under the homogeneous supply of OH^-ion, which is generated by hydrolysis of urea. Accordingly, iron(III) oxide hydroxide or similar compounds to the hydrolysis products of iron(III) ion was precipitated by the precipitation from homogeneous solution methods. Akaganeite (β-FeOOH) was crystallised from 0.1 M iron(III) chloride solution. Goethite(α-FeOOH) and hematite (α-Fe₂O₃) was precipitated from 0.1 M iron(III) nitrate solution, vigorous liberation of OH^- ion favoring the crystallization of hematite. The addition of chloride ion to the solution resulted in the formation of akaganeite. Basic salt of iron sulfate[NH₄Fe₃(OH)₆ (SO₄)₂] and goethite were formed from 0.1 M iron(III) sulfate solution, the former being obtained in the more moderate condition of the urea hydrolysis (<363 K) and the latter being produced in the more vigorous hydrolysis condition of urea (>363K).