Adsorption And Immobilization Of Heavy Metals In Soil And Water By Iron-rich Enviornmental Materiels

With the development of modern industry, more and more attention has been given to the influence of heavy metal pollution on eco-environment and human health. This paper deals with the adsorption and immobilization of heavy metals in soils and water by iron-rich environmental materials, such as flay ash, iron oxide tailing and bust furnace slag. The effects of contact time, pH, the initial concentration and ionic strength on the adsorption of heavy metal ions Cd²⁺, Pb²⁺, Cu²⁺ on magnetic materials separated from fly ashes were evaluated by using batch adsorption experiments. Based on the laboratory culture experiments of added iron-rich environmental materials to soils, the heavy metal chemical fractions and extraction concentrations by TCLP and EDTA procedures are analyzed. Results were as followings:The batch experiments showed that magnetic materials adsorbed rapidly heavy metals and reached equilibrium within 6 hours. The adsorption rate followed the order of Pb²⁺>Cd²⁺>Cu²⁺. The electrolyte intensity affected strongly adsorption capacity of Cu²⁺ and Cd²⁺ on magnetic materials. However, adsorption of Pb²⁺ on magnetic materials showed little differences in the range of 0.2 to 1.0 mol/L levels of electrolyte. The heavy metals adsorption on the magnetic materials tended to decrease with an increase of pH. The curves of isothermal adsorption of Cd²⁺, and Cu²⁺ on magnetic materials were well fitted by the Langmuir equation.The immobilization efficacy of iron-rich environmental materials (magnetic materials extracted from fly ash, iron mine tailing and steel slag) was evaluated by applying 5-stage sequential extraction, US EPA TCLP test and EDTA leaching test on the mixtures of iron-rich materials with two kinds of soils. The 5-stage sequential extraction results indicated that the application of iron-rich environmental materials resulted in changes of chemical fractions of heavy metals. The heavy metals were dominantly associated with Fe/Mn oxide fraction and least exchangeable fraction. The TCLP solubilities of Cd, Cu, Pb, Zn were reduced due to the addition of iron-rich environmental materials to soils. The EDTA leaching test indicated that the bioactive concentrations of heavy metals were also decreased. The results showed iron-rich environmental materials had a potential capacity of adsorption of heavy metals in thecontaminated soils.