An Ex-Situ Immobilization Experiment Of Heavy Metal Pollution In Coastal Sediments Of Bohai Bay By Bentonite

With the rapid development of coastal economy,the pollution situation in Chinese coastal zone has become more severe.As potentially hazardous pollutants in the coastal zone,heavy metals have received extensive attention due to their mobility,persistence and biological toxicity.The research object selected in this study is the tidal flat sediments of Dashentang,Bohai Bay,Tianjin.The improved BCR form extraction method is used to extract the acid-extracted state(F1),reducible State(F2),oxidizable state(F3)and residue state(F4)of the four heavy metals Zn,Cd,Pb and Cu.At the same time,bentonite is used as passivation agent to passivate the heavy metals in the sediments.The study analyze the changes of the occurrence of the four heavy metals under different environmental conditions,and the study also compare the passivation effect of the sediments under different proportions of bentonite dosage,different acid-base treatment,and different concentrations of pollution treatment of heavy metal liquid.And the passivation mechanism was discussed.The main conclusions include:(1)The addition of bentonite will cause the p H of the sediment to change.As the dosage of bentonite increases,the p H of the sediment fluctuates and rises with passivation time.And the greater the dosage of bentonite,the greater the p H change(2)The relationship between the percentage content of Zn and Cu in the sediments is the residual state> reducible state> oxidizable state> acid extraction state;Cd is dominated by acid extraction state,and Pb is reducible state> residue state > oxidizable state> acid extraction state.As the dosage of bentonite increases,the acid-extracted content of each metal gradually decreases,while the residue content increases.In acid-treated sediments,the morphological changes of all heavy metals are increased in acid-extracted state(active state),and alkaline-treated sediments have decreased in acid-extracted state(active state).Alkali-treated sediments will promote the inactivation of bentonite.And the higher the initial concentration level of heavy metals in the sediment,the higher the acid-extracted state content,and the less conducive to passivation.(3)Comparing the activity factors(ie MF values)of Zn,Cd,Pb and Cu in the sediments under different experimental conditions,the relationship between the MF values of the heavy metals is Cu<Zn<Pb<Cd.The calculation result of the MF values shows that bentonite has a good passivation effect when the dosage is 10%,and the passivation effect of Zn,Pb,Cu is better when the dosage is 10% and the passivation time is 60 days.Cd passivation effect is not obvious.