Monitoring of the Forced Hydrolysis of Fe[Cl.sub.3] Solutions in the Presence of Sodium Dodecyl Sulphate

Precipitations by the forced hydrolysis of 0.2 M Fe[Cl.sub.3] aqueous solutions between 2 and 72 hours in the presence of 1 % sodium n-dodecyl sulphate (SDS) were investigated. In the absence of SDS a direct phase transformation [Beta]-FeOOH [right arrow] [alpha]-[Fe.sub.2][O.sub.3] via dissolution/recrystallization occurred in the precipitation system. In the presence of SDS small amounts (traces) of [alpha]-FeOOH as an intermediate phase precipitated, and with a prolonged time of forced hydrolysis [alpha]-FeOOH also transformed to [alpha]-[Fe.sub.2][O.sub.3] via the dissolution/recrystallization mechanism. On the basis of Mossbauer spectra it was concluded that in the presence of SDS the [alpha]-[Fe.sub.2][O.sub.3] phase exhibited a lower degree of crystallinity. During the precipitation process in the presence of SDS the competition between the stability of Fe(III)-dodecyl sulphate on one side and the formation of iron oxide phases on the other also played an important role. Thermal field emission scanning electron microscopy (FE SEM) revealed that the big [alpha]-[Fe.sub.2][O.sub.3] particles possessed a substructure. The elongation of primary [alpha]-[Fe.sub.2][O.sub.3] particles produced in the presence of SDS was noticed. This effect can be assigned to the preferential adsorption of sulphate groups on nuclei and crystallites of FeOOH and [alpha]-[Fe.sub.2][O.sub.3] phases during the forced hydrolysis of Fe[Cl.sub.3] solutions. Keywords: Fe[Cl.sub.3] hydrolysis, sodium n-dodecyl sulphate, [alpha]-[Fe.sub.2][O.sub.3], [alpha]-FeOOH, XRD, Mossbauer, FT-IR, FE SEM.