Speciation of aluminium in surface water

A Chelex-100 ion exchange column was used for the separation of different dissolved aluminium species occurring in acidified waters in the Belgian Campine. The samples were filtered through Whatman-41 and 0.4 μm Nuclepore filters and the particulate aluminium was determined by instrumental neutron activation analysis (INAA). The filtrates were submitted to ion exchange in order to separate aluminium combined with humic acid, fluoride-complexed aluminium and free or hydrolyzed aluminium. The concentrations in the different fractions were determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). Humic acid, originating from the soil, is a main component of bogs. Due to its high complexing capacity with cations, it may decrease aluminium toxicity. The more toxic forms Al(OH) 2+ and Al(OH) 2 + still represent an important fraction of the total aluminium between pH 4 and 6, especially when the humic acid content is low. In general, the concentration of fluoride in the bogs, originating from atmospheric deposition, is too low to complex a major fraction of aluminium.