The Influence Of Different Colloids On The Transport Of Lead And Cadmium In Saturated Porous Media

Lead(Pb)and cadmium(Cd)are ubiquitous pollutions in the environment,the combined pollution of heavy metals usually exist in soil,the effect of Pb and Cd combined pollution have much different from the effects caused by single Pb or Cd,combined pollution would cause great damage for environment.A variety of inorganic,organic and their complexes colloids exist in natural soil,the colloids could act as a mobile media to advance the transport of sorbed heavy metals.The studies had showed the relationship between a single heavy metal and colloids,while there had less works focused on the transport of combined heavy metals and colloids in the porous media.The research on the interaction mechanism between Pb、Cd and soil colloid in saturated porous media will improve the understanding of the heavy metal colloid-facilitated transport in the media,providing the scientific theoretical guidance to the remediation of Pb and Cd pollution in soil.A series of column experiments were conducted to study Pb and Cd transport in porous media under various experiment conditions: colloidal solution(montmorillonite colloid,manual loessial soil colloid,humic acid and DI water),flow rate(0.1,0.5 and 1.0 ml min-1),sand grain size(0.4-0.8mm and 0.8-2.0mm)and characters of media.The results of the study are as follows:(1)Colloid promoted the transport of Pb and Cd,the effects of different types of colloids on heavy metal transport were not consistent.The data revealed that recovery rates for Pb from high to low was HA,manual loessial soil colloid,montmorillonite colloid and DI water,and recovery rates for Cd from high to low was manual loessial soil colloid,HA,montmorillonite colloid and DI water.The competitive adsorption of Pb is stronger than Cd in quartz sand surface and the transport of colloid in the quartz sand column revealed different behaviors,the mobility ability of colloid is HA > montmorillonite colloid > manual loessial soil colloid.(2)Higher flow rate gave rise to high mobility of heavy metals and colloid;increasing grain size influenced the retention and transport of Pb,Cd,montmorillonite colloid and Manual loessial soil colloid,except for HA.(3)HA-coated quartz sand decreased the transport of Pb,Cd and colloid in saturated porous media;increasing the amount of modified quartz sand in the columns,the adsorption capacity for heavy metals and colloid were improved;the effect of different type of colloids showed the different migration behavior for Pb and Cd,the main reason for the phenomenon were characters of media and colloids.(4)With the analysis of the transport characters of colloid,and the effect factors of flow rate,sand grain size and modified quartz sand on the transport of Pb and Cd,the result showed that the transport of Pb and Cd in saturated porous media were influenced by the characteristic of heavy metal ions and physical-chemical conditions,the key factors of the transport was properties of heavy metal ions.