Complexation of organic compounds in the presence of Al3+ during micellar flocculation

Complexes of Al and model pollutants phenol, benzoic acid, 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4-DB (2,4-dichlorophenoxybutiric acid) play a key role in the removal of organic pollutants by co-adsorption on micelles of anionic surfactants flocculated by means of Al3+. This technique, known as adsorptive micellar flocculation (AMF), is related to removal of organic compounds by coagulation–precipitation with Al and Fe salts. Some of the stoichiometries found (6Al:1L and higher, with “L” the organic compound) indicate that complexes of a cationic nature form in the presence of high excesses of Al, possibly polyaluminium complexes related to the species [Al13O4(OH)24]7+. In the case of phenol it has been established by spectroscopic measures that in the range of [Al2(SO4)3]tot between 5×10−5 and 3×10−4 M and [phenol]tot between 10−3 and 6×10−3 M complexes exist at pH as low as 2.4. The results show that AMF may be explained by the chemisorption of molecules of organic compounds able to incorporate into the polyaluminic complexes occurring within the Stern layer of flocculating micelles.