Influence of cations and anions on the formation of β-FeOOH

In the presence of cations such as Cr3+, Cu2+ and Ni2+, and anions such as SO42- and NO3-, precipitation of β-FeOOH from Fe3+-solution containing Cl− by hydrolysis have been investigated by means of X-ray diffraction technique (XRD), Mössbauer spectroscopy (MS) and transmission electron microscopy (TEM). XRD peaks of β-FeOOH were broadened when the cations were added as sulfates, and this tendency for Cr3+ was significantly observed. When the cations were added as nitrates, there was no significant change in XRD peaks. Inductively coupled plasma (ICP) analysis showed that only Cr added as sulfate was contained in β-FeOOH. Ni and Cu added as sulfates, and any cations added as nitrates were not contained in it. When β-FeOOH was synthesized with Na2SO4, the XRD peaks were broadened. XRD-peak broadening was mainly caused by the coexistence of SO42- ion. The incorporation of cations in β-FeOOH is affected by coexistent anions, and the XRD-peak broadening is caused by not only cations but also anions. This behavior has been discussed in association with the stability of Fe3+-complexes in the solution.