ON AMORPHOUS Al(OH)3 IN DRINKING WATER SUPPLY NETWORKS

Trace metal elements commonly exist in drinking water. Excessive exposing on them may result in lots of health problems. This paper mainly focuses on the accumulations of Cu 2+ , Cd 2+ , and Pb 2+ in drinking water supply networks with amorphous Al(OH)3 formation. The effects of pH, water flow rate, and metal element contents were investigated at laboratory bench scale. It was found that chemical adsorption mainly occurred at pH > 7.0. Suspended Al(OH)3 showed a strong adsorption capacity for Cu 2+ , Cd 2+ , and Pb 2+ ; 1.0 g Al(OH)3 could accumulate 43.0 mg of Cu 2+ , 30.0 mg of Cd 2+ , and 34.6 mg of Pb 2+ at 15℃, respectively. Thermodynamic calculation results indicated nearly all of the Cu2+ and Cd2+ were adsorbed at pH 6.5-8.5, chemical precipitation did not occur in the presence of suspended Al(OH)3. Because of H + inhibition, the adsorption of Cu 2+ , Cd 2+ , and Pb 2+ would be inhibited under acidic condition. Unlike suspended Al(OH)3, Al(OH)3 scale showed a much lower adsorption capacity for Cu 2+ , Cd 2+ , and Pb 2+ , at approximately 0.4, 0.4, and 0.7 mg/g, respectively; and the variation of flow velocity and solution pH had minor effects.