CHARACTERIZATION OF AMORPHOUS ALUMINUM HYDROXIDE BY THE FERRON METHOD

Characterization by the ferron method of the solid formed during hydro lysis of aqueous aluminum(III), under conditions of water and wastewat er treatment, is the focus of the present study. It has been found-tha t the rate of reaction (later referred to as aluminum reactivity) betw een freshly precipitated amorphous aluminum hydroxide and the reagent containing a reduced form of ferron may be used to characterize the pr ecipitate. With increasing age between 1 min and 45 d, the reactivity of aluminum in the precipitate was found to steadily decrease. For exa mple, 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 10 0 min. The aluminum reactivity was also substantially affected by the presence of phosphate and organic matter, but only slightly by the cou nteranion (Cl-, NO3-, and SO42-) of the aluminum salt. As well, it was found that reactivity with the reagent was influenced by the intensit y of mixing used during the coagulant addition process and that well-m ixed situations led to a more reactive aluminum. An investigation of t he properties of samples taken from water and wastewater treatment pla nts is also briefly discussed.