ADSORPTION OF HUMIC ACIDS ONTO PREFORMED ALUMINUM HYDROXIDE FLOCS

Humic substances are acidic, coloured, chemically complex polymeric macromolecules. They are naturally occurring constitutents of soil, sediment and surface water. Much of the reactivity of humic substances in aqueous solution is attributed to their functional groups that contain oxygen, including carboxyl, carbonyl, phenolic and methoxyl; carboxyl and phenolic groups provide most of the negative charge that adds to the mobility of humic substances in the environment, and are believed to react with metals (Edwards and Amirtharajah, 1985; Mantoura et al., 1978; Vik et al., 1985; Chadik and Amy, 1987; Backes and Tipping, 1987). For water treatment, aluminum salts are the most widely used coagulants. Therefore it is necessary for the water specialist to have a good knowledge of the chemistry and the speciation of aluminium in the aqueous environment. Because of the complicated chemistry of aluminium in this environment, many researchers disagree about the exact nature of hydrolysed species and the mechanism (reaction) involved in the coagulation-flocculation process (Dempsey et al., 1985; Randtke, 1988; Hundt and O'Melia, 1988; Dentel and Gossett, 1988; Jekel, 1986a, b; Tipping et al., 1988a, b). Specific conditions and aluminium species that exist during the charge neutralization-precipitation-adsorption and simultaneous precipitation reaction mechanisms are often discussed (Hundt and O'Melia, 1988). The objectives of the research presented here were only to evaluate the removal of humic substances, humic acids, fulvic acids by preformed flocs, to compare the adsorption capacities of the flocs to the capacities of other adsorbing materials such as activated carbon and ionic exchange resins.