Adsorption de substances humiques sur flocs d'hydroxyde d'aluminium preformesAdsorption of humic acids onto preformed aluminium hydroxide flocs

Introduction. Humic substances are acidic, coloured, chemically complex polymeric macromolecules. They arc naturally occurring constituents 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, aluminium 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 the hydrolysed spedes and the mechanism (reaction) involved in the coagultion-flocculation process (Dempsey et al., 1985; Randtke, 1988; Hundt and O'Melia, 1988; Dentel and Gossett, 1988; Jekel, 1986a, b; Tippin8 et a/., 1988a, b). Specific conditions and aluminium species that exist during the charge neutralixation-precipitation-adsorption and simultaneous predpitaon reaction mechanisms are often discussed (Hundt and O'Melia, 1988).

The objectives of the research presented here were only to evaluate the removai of humic substances, humic acids, fulvic acids by preformed fioes, to compare the adsorption capacities of the fiocs to the capacities of other adsorbing materials such as activated carbon and ionic exchange resins.