Soil Heavy Metals Of Cu, Cd, Zn And Pb Adsorption And Migration Of The Experimental Study

Heavy metal ions are the most toxic inorganic pollutants which occur in soils and can be of a natural or of anthropogenic origin such as the application of fertilizers,sewage sludge,liming materials,and other industrial and urban waste materials.The heavy metals witch are introduced into the soils either accumulate in the surface layer or transport into the groundwater.Adsorption is a major process responsible for accumulation of heavy metals.Therefore the study of adsorption processes is of utmost importance for the understanding of how heavy metals are transferred from a liquid mobile phase to the surface of a solid phase.The mainly objectives of the present study are to evaluate the adsorption and competitive adsorption of four heavy metals(Cu,Cd,Zn,Pb) in three types of soils in Qingdao,shandong Province by means of sorption isotherms and distribution coefficient(K_d),to evaluate the capacity of these soils to sorb these metals,to establish the selectivity sequences of the metals(Cd,Zn) in these soils,and to investigate the relationship between soil properties and the adsorption of these metals by soils.The isothermal and static adsorption experiment was conducted and the conclusions below were drawn:The amount of heavy metals adsorption increases with increasing concentration and the relationship could be described by the Langmuir,Freundlich and Temkin isotherms,and the Freundlich isotherm is better than Langmuir and Temkin isotherms.It indicates that the adsorption ratio is related to the heavy metal concentration in the solution.The capacity of the adsorption by the Lime concretion black soils is much larger than that of the Brown soils and Fluvo-aquic soils due to their high pH,high content of organic matter and clay.The sequence of the capacity of the four heavy metals adsorption by the soils is Pb＞Cu,Cd＞Zn according to the distribution coefficient K_d.The sequence of the Cu,Cd is related to their concentrations in the equilibrium solution,that is,the capacity of Cu adsorption is larger than that of Cd under the low concentration and vice versa.The high capacity of lead adsorption by soils is mainly for that as the lead is introduced into the soils,it easily and quickly forms insoluble complexes.The contaminated soils typically contain high amounts of various metals that compete with each other for sorption sites.The selectivity capacity of the Zinc is stronger than Cadmium because the higher hydrolysis capacity of Zinc and the formed hydroxyl-metal complexes are much more easily sorbed than free heavy metal ions.The sum of the coexisting Zinc and Cadmium adsorption is larger than the single Zinc or Cadmium, indicating that there are some sorption sites special for the Zinc or Cadmium.The amount of the Zn(Cd) adsorption decreases with the increasing concentration of Cd(Zn) and extrapolates that the amount reaches a constant finally,and here the specific adsorption dominates.In order to make clear how the heavy metals transport and transfer in the soils,a miscible displacement approach,where soil columns under soil-water-saturated conditions and constant flow velocity were maintained,was carried out.The primary study of the Zn,Cd transport in columns was conducted and found out that,the Zn,Cd is significantly retarded in the three types of soil especially in the Lime concretion black soils;the mobility of Zn in the soil columns is faster than Cd;no physical non-equilibrium phenomenon exists and there is a chemical non-equilibrium phenomenon existing in the transport process,witch is related to the rate-limited adsorption.