CHARACTERIZATION OF AMORPHOUS ALUMINUM HYDROXIDE BY THE FERRON METHOD

Characterization by the ferron method of the solid formed during hydrolysis of aqueous aluminum(III), under conditions of water and wastewater treatment, is the focus of the present study. It has been found-that the rate of reaction (later referred to as aluminum reactivity) between freshly precipitated amorphous aluminum hydroxide and the reagent containing a reduced form of ferron may be used to characterize the precipitate. With increasing age between 1 min and 45 d, the reactivity of aluminum in the precipitate was found to steadily decrease. For example, a t(50) value (indicating the time for 50% recovery of the added aluminum) for a 1-min aged aluminum hydroxide was found to be near 10 min, while for the 10 000-min aged sample the t(50) value was near 100 min. The aluminum reactivity was also substantially affected by the presence of phosphate and organic matter, but only slightly by the counteranion (Cl-, NO3-, and SO42-) of the aluminum salt. As well, it was found that reactivity with the reagent was influenced by the intensity of mixing used during the coagulant addition process and that well-mixed situations led to a more reactive aluminum. An investigation of the properties of samples taken from water and wastewater treatment plants is also briefly discussed.