Research On The Remediation Of Heavy Metal Contaminated Field By Amendment Product

Heavy metals with high toxicity,difficult to degrade and persistence and other characteristics has been widely concerned by domestic and foreign scholars.Heavy metal contaminants due to human activities cause serious harm to ecosystem and human health.The aim of this research was to study the remediation of heavy metal pollution by using the prepared mineral amendment to remove Pb and Cd from water and to repair Pb-contaminated soil.The effects of the dosage of amendment,pH of solution,initial concentration of heavy metal ions,contact time and temperature on the adsorption process were studied by adsorption experimentally.The results showed that the initial concentration of lead was 800 mg/L,the concentration of cadmium was 25 mg/L,the pH was 4.0,the adsorption time was 150 min,the dosage of amendment was 2.5 g/L,the temperature was 25?,the removal rate of lead and cadmium were more than 86%.The adsorption capacity of lead and cadmium were increasing with the temperature.The adsorption processes of lead and cadmium were consistent with pseudo-second-order model and correlation coefficients were 0.999 and 0.998,respectively.This adsorption process contained all the processes of physical adsorption and chemical adsorption,but mostly based on chemical adsorption.Langmuir and Freundlich models could well fit the adsorption processes of lead and cadmium by the amendment.At the temperature of 25?,the maximum adsorption capacity of lead and cadmium in the monolayer were 316.969 mg/g and 9.101 mg/g,respectively.The thermodynamic calculation of ?G<0,?S>0 indicating that the amendment on lead and cadmium sorption processes were spontaneous reaction;?H>0 indicates that the reaction process is endothermic and higher temperature is more conducive to sorption.At the same time,the effects of pH,contact time and initial concentration of lead and cadmium on adsorption were discussed in mixed solution.The sorption mechanism of mineral amendment on lead and cadmium was discussed by X-ray diffracition analyzer(XRD),scanning electron microscopy(SEM)and X-ray photoelectron(XPS).The results showed that the removal efficiency of lead and cadmium achieve best when the pH was 5.0 and the contact time was 150 min in the mixed solution.Lead and cadmium adsorption process were consistent with pseudo-second-order model and the sorption capacity of lead and cadmium decreased by 3.7% and 55.69%,respectively.XRD characterization of the residue before and after the adsorption of the amendment showed that PbSO4 and Pb(OH)2 were formed after Pb reaction,CdCO3 was formed after reacted with Cd solution.PbSO4 and Pb(OH)2 were formed after sorption mixed solution,but no Cd-containing compound.SEM maps can be seen that a large number of filaments adhere to the surface of mineral after sorption Cd.After sorption of Pb,the columnar structure minerals are further reduced and flaky structure is increased,it indicated that adsoption or precipitate reaction happened between amendment and Pb.The effects of the amendment on soil pH,heavy metal leaching concentration,heavy metals distribution and contents of mineral element were studied to evaluated the restorative effects on the remediation of heavy metal contaminated soil with soil culture experiment.The results showed that the application of amendment increased the p H of soil by 0.33 to 2.62 units,and significantly reduced the acid extractable fraction of heavy metal and changed to the more stable form.The acid extracted fraction of lead decreased up to by 39.01% when addition rate was 6 g/kg.The application of amendment improved the content of available Ca,Mg and Si on soil.The correlation analysis showed that there was a significant negative correlation between content of mineral elements in the soil and the acid extracted fraction of Pb.The correlation coefficients between exchangeable Ca,available Si and acid extracted Pb are RCa=-0.725* and RSi=-0.654*,respectively.The mid-experimental results showed that the leaching concentration of lead was lower than 0.001 mg/L and pH were between 7.47 and 8.16,which meets the evaluation standard of remediation contaminated sites in the United States.It has a good remediation of this amendment on lead contaminated soil.