Effect Of Microwave-assisted Hydrogen Peroxide Xidation On Heavy Metals In Sediment And Fesibility Of This Method To Remediate Sediment

Sediment pollution has been recognized as a serious problem of environmental pollutionthroughout the world. Many countries and regions have this problem.Chemical oxidationis an effective approach to treatment of organic pollutants in sediment, which could degrade most organics.However, the chemical oxidation method may change the characteristics of sediment and the environment of heavy metals in sediments, causing the release of heavy metals and even leading to t he secondary pollution of heavy metals. But there is no study on the release mechanism of heavy metal in the process of. Therefore, this study adopts advanced chemical oxidation processes of microwave assisted hydrogen peroxide oxidation to treat sediment obtained from Xiawan River in Zhuzhou, Hunan province, studying the release behavior of heavy metals from sediment. Also, the effects of the initial p H value, the concentration of hydrogen peroxide, the microwave reaction temperature and microwave reaction time on the release of heavy metals in sediments were investigated.This study found that the chemical oxidation of microwave assisted hydrogen peroxide can cause the release of a large number of heavy metals in sediments. On this basis, whether this technology can be a promising method to treat heavy metalpollution in sediment was further explored.First of all, as a kind of advanced oxidation technology,microwave assistedhydrogen peroxide oxidation technology can greatly improve the redox potential and reduce final p H value of sediment slurry,thereby greatly enhancing the release of heavy metals in sediment. The high redox potential in sediment slurry can degrade organic substances, thus leading to the release of heavy metals bonding in organic matters.Meanwhile, acidic substances released from the oxidation process, thep H value of the sediment slurry was reduced, further enhancing the release of heavy metals.Secondly,the release efficiency of Cu and Pb increasedrapidly with the hydrogen peroxideconcentration from 0 M to 0.2 M. For Cd, thehighest release efficiency was reached at the hydrogen peroxide concentrationof 0.1 M.While the hydrogen peroxide concentrations had no effect on Zn.The microwave reaction temperature and microwave reaction timehad remarkable effect on therelease efficiency of Cu and Pb.The release efficiency increasedwith increasing microwave temperature from 25°C to 85°C for Cu and Pb.When thetemperature of slurry was 50 °C, the release efficiency of Cuand Pb increased with increasing microwave time from 0 minto 6 min and then became stable.Thirdly, BCR(Community Bureau of Reference)sequential extraction experiments showed that there is a tight relationship between the release efficiency of heavy metals from the sediment and the chemical speciation insediment.In the process of chemical oxidation of microwave assisted hydrogen peroxide treatingheavy metals in sediment, the chemical speciation of heavy metals in sediments greatly determines the release efficiency of heavy metals.Microwave assisted hydrogen peroxide oxidation technology can lower the content of heavy metals in acid soluble/exchangeable, reducible, andoxidizable respectively, and higher the content of heavy metals in residual form. After treatment by this process, the metals in the sediment have higher stability and thuslower risk to the environment.Finally, the microwave assistedhydrogen peroxide oxidatio n technology just can solve part of the heavy metals harm and some heavy metal heavy metals in sediments rather than all the harm of heavy metals insediments.For extremely highsediment pollution(such as sediment from Xiawan River), this technology cannotcompletely solve the problem.While for other sediment samples, this techniquecan greatly reduce the hazards of heavy metals, but still cannot solve problem of some heavy metals.For the high pollution of heavy metals Cd and Zn, they cannot be addressed.For heavy metals Cu, Pb and Cr, the content are relatively high, and thistechnology can solve the problems of this three heavy metals pollution in sediment.In brief, the release behavior of heavy metals during treatmentof dredged sediment bythe chemical oxidation of microwave assisted hydrogen peroxide was investigated in this study.The mechanisms of the heavy metals release and the effect of this chemical oxidation process on heavy metal speciationwere preliminarily explored. Also, the feasibility of whether this chemical oxidation technology could be a method to remediate sediment contaminated with heavy metals was evaluated, providing a case study for other researches.