CHARACTERIZATION OF AL(III) SPECIES IN BA SIC ALUMINUM-CHLORIDE FLOCCULANTS BY MEANS OF FERRON METHOD AND AL-27 NUCLEAR-MAGNETIC-RESONANCE

Flocculant processes as a treatment step in water and wastewater purif ication technology are of increasing importance. Partially neutralized aqueous aluminium chloride solutions - the basic aluminium chlorides - are often used as flocculants in water conditioning. The present pap er describes the reactions which appear in these solutions by their di lution, the identification of occurring cationic aluminium species, an d the relations between the composition of the solutions and their eff iciency as flocculants. The solutions were quantitatively analyzed usi ng Al-27 NMR and the ferron method; the latter method offers a simple and inexpensive alternative for identification and quantification of a luminium cations and can facilitate investigations of the Al speciatio n at concentrations too low for analysis by NMR. The distribution of a luminium cations in basic aluminium chloride solutions changes drastic ally by the dilution while applied as flocculants because the equilibr ium strongly depends on the concentration. The dynamic changes followi ng the dilution of partially neutralized solutions were investigated s imply by mixing a solution with water and immediate analysis by the fe rron method. It could be shown that rearrangement reactions occur in t he system, partially overlapping each other; the oligomeric cations se em to be especially instable. Furthermore, a partial change from octah edral to tetrahedral coordination of the aluminium in the species can be observed. At extremely low aluminium concentrations, as in the case of application of the basic aluminium chloride solutions for floccula tion, monomeric and especially transition polymeric and polymeric alum inium cations, respectively appear. The ratio of these cations to each other also depends on the time up to the flocculation. Accordingly, t hese cations especially the different polymeric aluminium species seem to be important for the efficiency of the basic aluminium chlorides a s flocculants in water conditioning.