To examine the influence of silicate ions on a conversion process of condensed ferric hydroxide (Fe(OH)3) gel to ferric oxyhydroxides and iron oxides, the Fe(OH)3 gel was aged at 60°C in the presence and absence of silicate ions. Fine particles and supernatant solution were sampled from the aged suspensions containing colloidal particles. Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used for characterizing the resulting solid particles. XRD profiles and TEM micrographs showed that the Fe(OH)3 gel transferred into β-FeOOH and α-Fe2O3 particles by aging in the absence of silicate ions. On the other hand, silicate ions suppressed the conversion of the Fe(OH)3 gel to β-FeOOH and α-Fe2O3 particles. The conversion of the Fe(OH)3 gel to α-Fe 2O3 particles is almost independent of pH of solution under the conditions in the present study, indicating that silicate ions essentially suppress the formation of β-FeOOH and α-Fe 2O3 particles.
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