Adsorption-desorption Characteristics Of Typical Heavy Metal Pollutants In Sediment Of The Hyporheic Zone

Hyporheic zone is the interface between surface water and groundwater.In the hyporheic zone,pollutants-water-soil-air interaction,surface water and groundwater contact,mix and react fully.Under the action of natural water flow,most heavy metal pollutants will adsorb on the sediment in the hyporheic zone when they enter the aquatic environment,under certain conditions,the heavy metal pollutants will be desorbed from the sediment,which will cause the secondary pollution of water environment.Therefore,it is of great significance to study the adsorption-desorption characteristics of typical heavy metal pollutants in the sediments of the hyporheic zone.In this paper,the sediments of Jialu River in Zhengzhou City were selected as test samples to study the adsorption-desorption characteristics of typical heavy metal pollutants Cd,Pb,Cu and Zn in the sediments of the hyporheic zone.The effects of various factors on the adsorption-desorption process of typical heavy metal pollutants in the sediments were discussed,such as reaction time,initial concentration,solid-liquid ratio,temperature,pH,organic matter,etc The competitive adsorption characteristics of four heavy metal pollutants in the binary system were also studied.Conclusions are drawn as follows:The pseudo second order kinetic model can well simulate the adsorption kinetic process of four heavy metals in the sediments of the hyporheic zone.The order of adsorption rate of the four heavy metals in the sediments is: Cu>Pb>Cd>Zn.The elovich equation can well simulate the desorption kinetics of the four heavy metals in the sediments of the hyporheic zone.The order of desorption rate of the four heavy metals in the sediments is:Cd>Cu>Zn>Pb.The sediments in the hyporheic zone have strong adsorption ability to the heavy metals and are not easy to be desorbed after adsorption.The adsorption of the heavy metals is mainly based on ion exchange,and the adsorption isotherms can be classified as “L” type.Freundlich model is better than Langmuir model and D-R model in fitting the adsorption isotherms.The adsorption capacity and desorption capacity of four heavy metals increased with the increase of temperature,and the proportion of desorption capacity to adsorption capacity also increased.The adsorption process of four heavy metals was spontaneous and endothermic.With the increase of pH value,the adsorption capacity of four heavy metals increased and the desorption capacity decreased.After the removal of organic matter,the adsorption capacity of four heavy metals in the sediments of the hyporheic zone decreased,while the desorption capacity increased.In the binary competitive adsorption system,most of the heavy metals adsorbed by the sediment in the hyporheic zone can be classified as “L” type,and the selective order of the heavy metals adsorbed is: Pb>Cu>Zn>Cd.