Research On The Transferring Rule Of Heavy Metal In The Process Of Flocculating The Dredged Sediment

Dredging is the widest applicable treatment for sediment at present. The sedimentdredged out needs to be dewatered by flocculent precipitation method commonlyadopted in engineering. In the process of flocculating and dewatering, the transferringand conversion of heavy metal and other pollutants in sediment influences the treatmentof subsequent residual water and utilization of dewatered sediment. thus this researchdiscussed the transferring rule of heavy metal in the process of flocculating the dredgedsediment. The aim of the study is providing theoretical foundation for the treatmentprocess for dredged sediment polluted by heavy metal.Through lab-scale study of the dewatering process of dredged sediment, theinfluences of flocculants, coagulant aids, ameliorant, pH value of sediment, organicmatter in sediment and other factors on four heavy metals transferring behavior werestudied and the changes of the speciation of the four heavy metals were analyzed. Themain conclusion of research is as below:(1) In the process of flocculating and dewatering the sediment, the coagulant haslittle influence on the transferring of Chromium, Cadmium and Zinc while can promoteArsenic to precipitate in solid phase of the dredged sediment. the coagulant plus PAMhas little influence on Chromium’s transferring behavior while can promote Arsenic toprecipitate in liquid phase and Cadmium and Zinc to precipitate in solid phase. The lime,as a kind of modified agent,also has little influence on Chromium’s transferringbehavior while can promote Arsenic, Cadmium and Zinc to precipitate in solid phase.(2) In the flocculating and dewatering process, the increase of sediment pH valueis favorable for Cadmium and Zinc to precipitate in solid phase and has a little influenceon Chromium and Arsenic’s transferring behaviors. the increase of organic contents isfavorable for Chromium, Cadmium and Zinc to precipitate in solid phase and hasreverse effect on Arsenic.(3) Four heavy metals in dewatered sediment have different speciationdistribution, for example, chromium is mainly in oxidation fraction, weak acid extractfraction and residual fraction. Cadmium is mainly in weak acid extractedfraction,reduction state and residual state. Zinc is mainly in weak acid extracted fraction,residual state and reduction fraction. Arsenic is mainly in residual and reduction fraction.The PAM have the risk of promoting the release of Chromium, Cadmium and Zinc.