| A kind of granular modified peanut shell which show good results in cadmium adsorption was used as absorbent for cadmium (II) removal in a fixed bed. Dynamic Adsorption characteristics of cadmium (II) in water on modified peanut was studied so as to provide theory foundation for its industrialized application in fixed bed and in situ adsorption. This paper studies the dynamic Adsorption characteristics of Cd and Pb-Cd system respectively. The effects of experimental parameters, such as pH, initial concentration, feeding flow velocity and adsorbent particle size on Cd adsorption were studied. Besides, Some research on recovering cadmium was carried in this experiment. Through analysis of experimental results of different cases, Conclusions below were obtained:(1) The unit bed pressure drop is very small and it increases grows with increasing of feeding flow velocity and bed height. When the bed height was40cm, The relationship between feeding flow and unit bed pressure drop can be described as the equation:△p=0,65054+0.0183v+0.0501v2The higher the bed depth is the greater the unit bed pressure drop is, and they showed a linear relationship. When the flow velocity was33.44cm/min, it meet the equation:△p=1.3522z+2.0273(2) This result indicated that the column packed with modified peanut shells has shown good adsorption properties on cadmium (Ⅱ) removal.cadmium (Ⅱ) concentration in outflow could be less than0.001mg/L when initial concentration in in-flow is among0.55～11mg/L. According to different operating conditions the operation time reaches1-62h. Modified peanut shell is a kind of potential adsorbent for cadmium removal. It can be used for fixed-bed adsorption and in situ adsorption to water remediation.(3) The height of mass transfer zone was primarily driven by initial concentration, influent flow rate and adsorbent particle size. The order of the influence on the height of mass transfer zone was:adsorbent particle size> influent flow rate> initial concentration. The height of mass transfer zone kept substantially unchanged and the breakthrough ti increased with the bed height increased. The height of mass transfer zone increased and breakthrough time decreased with the elevated initial concentration, influent flow rate and adsorbent particle size.(4) The bed depth service time (BDST) model, Yoon and Nelson model and Wolborska model were used to analysis the experiment data. Wolborska model is not satisfactory for simulating the adsorption dynamic processes. BDST model, Yoon and Nelson model can be used for the adsorption dynamic processes simulation and predicting the operation time under low concentration. In this two models BDST model is more suitable.(5) The dynamic multicomponent competitive adsorption model was developed in modified Peanut shell bed. The numerical solution obtained by the model and the breakthrough curves assumed a certain coincidence. It indicated that cadmium was weakly-adsorbed species while lead was strongly-adsorbed.(6) The desorption capacities of four reagents:pure water, nitrate, sodium chloride and EDTA, would be affected slightly by temperature and concentration. Titrate was a most excellent desorption reagent obviously, the desorption rate is above91%. |
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