Interaction of Humic Substances and Aluminum Formation of Insoluble Associates

Mira Petrović and Marija Kaštelan-Macan

Faculty of Chemical Engineering and Technology, Laboratory of Analytical Chemistry, Marulićev trg 19, 101100 Zagreb, Croatia

Article history:
Received  May 17, 1996 
Accepted June 18, 1996

Key words:
Mimic substances, humic acid, fulvic acid, Al(1T1)-ion interaction

Summary:
The interaction of aluminum with soil humic (HA) and fulvic acids (FA) and formation of insoluble associates have been studied under laboratory conditions. The standard test procedure involved a series of experiments at one humic (and fulvic) concentration (50.0 mg/L and 68.5 mg/L, respectively) with varying concentrations of Al(III)-ions (0.5-5 mmol/L). The amounts of aluminum and humic substances precipitated where measured in the pH range from 2 to 10. It was found that, at any pH and regardless of mass ratio AI/HA, more than 85% of HA precipitate with aluminum. The formation of insoluble Al-fulvate is a pH-dependent reaction with precipitation maximum between pH=4-6. Tlie principal mechanism in an acidic medium (pH 5) is complex formation through salicylate-type functional groups with binding capacity (at pH=4) 2 mmol Al/g HA and 3.8 mmol Al/g FA. At higher pH the reaction mechanism is primarily sorption of humic substances on "in situ" formed Al(OH)₃.