Speciation of Al(III) with some classes of ligands in aqueous solution

In this thesis, Al3+ speciation with several ligands of environmental and biological interest was studied. A research of literature data concerning its speciation in natural fluids and the acid - base behaviour of the ligands under study was the first step. The analysis of different Al(III)-ligand systems was, moreover, preceded by an experimental investigation on the metal cation hydrolysis, in different ionic media and ionic strength. Ligands chosen for this study can be distinguished by their organic or inorganic nature, the class of their compounds and the functional groups present in the molecules (-COOH, -PO43-; -SH, -NH2), classifying them as O-, S- and N-donors. Their properties will be discussed later. On the light of the above considerations, the experimental analysis was developed in the following way: 1. Study of aluminium hydrolysis; 2. Determination of ligand acid - base properties; 3. Study of the Al(III) interactions with the different ligands under a wide range of experimental conditions. Stability constants of the species and speciation models were determined by means of potentiometric measurements. Enthalpy changes were obtained by calorimetric titrations. For some systems were also performed UV-spectrophotometric, 1H or 31P-{1H} NMR and MALDI-MS investigations. 4. Evaluation of the sequestering ability of the various ligands towards aluminium cation under different conditions.