Stabilization of Cd and Pb in the contaminated soils by applying modified fly ash

This study investigated the stabilization of heavy metals by adding modified fly ash(FA)to contaminated soils,and two similar materials,NaOH-zeolite(ZE)and natural zeolite(ZO)were introduced into the soils for comparison.Column leaching tests were conducted to analyze the difference of stabilization effects between the three materials.Leaching columns were run for 6 months,and a considerable stabilization of heavy metals in the soils was observed.The concentration of cadmium(Cd)and lead(Pb)in the amended soil substantially decreased(p<0.05).The results indicated that after 11 weeks of column leaching,Cd and Pb concentrations in the soil leachate decreased to below the detection limit due to amendment stabilization.Among the three amendments,the ZE amendment showed the optimum capacity for heavy metal immobilisation in the soils.In addition,after 6 months of leaching,Pb and Cd concentrations in the soils with the three different amendments decreased to various degrees.The amendments of modified FA and ZE were better than those of natural ZO.Coal FA,after modification,is a useful amendment for the remediation of heavy metals in the contaminated soil.

Removal of lead(Pb(Ⅱ))and zinc(Zn(Ⅱ))from aqueous solution using coal fly ash(CFA)as a dual-sites adsorbent

Coal fly ash(CFA)is composed of minerals containing some oxides in crystalline phase(i.e.,quartz and mullite),as well as unburned carbon as mesoporous material,thus enabling CFA to act as a dual-sites adsorbent with unique properties.This work focused on the adsorption of Pb(Ⅱ)and Zn(Ⅱ)from binary system,a mixture containing two metal ion solutions present simultaneously,onto NaOH-modified CFA(MCFA).Several adsorption tests were conducted to evaluate the effect of several parameters,including pH and contact times.The experiment results indicated that chemical treatment of CFA with NaOH increased pore volume from 0.021 to 0.223 cm^3·g^(-1).In addition,it could also enhance the availability of functional groups on both minerals and unburned carbon,resulting in almost 100%Pb(Ⅱ)and 97%Zn(Ⅱ)adsorbed.The optimum pH for adsorption system was pH=3 and quasi-equilibrium occurred in 240 minutes.Equilibrium data from the experimental results were analyzed using Modified Extended Langmuir(MEL)and Competitive Adsorption Langmuir-Langmuir(CALL)isotherm models.The analysis results showed that the CALL isotherm model could better describe the Pb(Ⅱ)and Zn(Ⅱ)adsorption process onto MCFA in binary system compared with MEL isotherm model.