Cadmium adsorption by sediment in a turbulence tank

The mechanism of sediment motion that affects cadmium (Cd) adsorption on se diment particles was studied in a turbulence tank in the presence (and abse nce) of bed mud. The experimental results were verified by a mathematical m odel for heavy metal transport-transformation developed for the turbulence tank. The mathematical model includes the equations of water Row, sediment motion. heavy metal transport-transformation. heavy-metal reaction kinemati cs and equations for prescribing the initial conditions and boundary condit ions for the experiment. The model conforms the transport transformation of heavy-metal pollutants in surface waters to following the law of convectiv e-diffusive of common tracers and the characteristics of fare and transport of sediment motion. Variations of dissolved Cd concentrations and suspende d particulate Cd concentrations with time and in the water column were meas ured and computed. The experimental measurements correspond with the comput ed results. Both the experimental measurements and computed results show th at it takes about 6 h to reach equilibrium condition for cadmium adsorption by sediment particles. This is different from the result obtained from exp eriments conducted in continuously stirred tank reactors (or batch reactors ) in which adsorption equilibrium can be achieved in about 20 min. Determin ation of the model parameters for sediment adsorption-desorption of metals in the tank is discussed. The experimental and computed results obtained in this study are useful to solve practical engineering problems in surface w aters. (C) 2001 Elsevier Science Ltd. All rights reserved.