Study On The Stabilization Of Copper And Lead From River Sediments Produced By Treatment Of Heavy Metal Pollution

Commonly, the emergency measure of sudden heavy metal pollution accident in waters is to dose the alkali and coagulant, by means of adsorption and sedimentation, making the heavy metal concentration up to water quality standard for water supply. However, in high-concentration heavy metal pollution incident, the conventional coagulation technology for emergency treatment is difficult to ensure the removal efficiency. Meanwhile, the sediments have potential risk to cause secondary pollution. Due to the particularity of structure and properties of bentonite, apatite, variable charge soil, they have certain adsorption and fixation capacity for heavy metal.To explore the feasibility that these minerals applied to emergency water treatment for copper and lead pollution, this study investigated the effect of single mineral additive(bentonite, apatite, variable charge soils) or apatite and zero valent iron as composite additives for enhance coagulation, simulated the formation of sediment in the emergency treatment process of heavy metal pollution accidents, and characterized speciation distribution of Cu and Pb in sediment to study the function of these minerals additives and the Cu and Pb fixed and release kinetics of the sediment involving these minerals additives, in order to provide a reference for the emergency measure of sudden heavy metal pollution accident. Moreover, this research investigated the effect of environmental factors on Cu and Pb release from sediment involving different mineral additive by regulating the pH, dissolved oxygen(DO), salinity and humic acid content of the overlying water and regulating the humic acid content and disturbance of the sediment.Experimental results are as follows:(1) The results of static release experiments indicated that the heavy metal released from the sediment decreased significantly with the addition of bentonite, apatite or variable charge soils and the fix rates could be ordered as follow: bentonite>apatite>variable charge soils. Adding bentonite, apatite or variable charge soil had less environmental impacts on water and sediment. Adding bentonite or apatite would increase the pH of the water but the addition of variable charge soil would reduce it. The Addition of bentonite, apatite or variable charge soils had less impacts on the DO value of the water, the redox potential(Eh) of sediment and the content of the total Fe of the water. The fraction of Cu and Pb in the sediment with bentonite, apatite or variable charge soils transferred from acid exchangeable state which have high biological effectiveness to reducible, oxidizable and residual state which have low bioavailability in the 45 days.(2) Main influencing factors affected the Cu and Pb release of the sediment greatly. The overlying water under low concentration of dissolved oxygen, at a high pH value, with low salinity and under static condition decreased the migration of Cu and Pb. However, the effect of humic acid on heavy metal release was complicated. The effect of DO on heavy metal release could be ordered as follow: weak oxidizing environment>oxidizing environment>anoxic environment. At low pH values, the heavy metal released rapidly from the sediment. The heavy metal release accelerated with the salinity increased. Presence of humic acid(HA) in water would reduce the release of Cu and Pb. For the control group, presence of fulvic acid(FA) in water would increase the heavy metal release in the early, and then were similar with the group which not added humic acid. The heavy metal release of other groups adding FA and minerals additives was relatively stable fluctuations. When sediments were added with HA, the release of Cu and Pb decreased, but added FA significantly increased the release of Cu and Pb. Compared to the control group, after adding humic acid and fulvic acids to the sediment, the proportion of acid exchangeable and reducible state changed little, while the proportion of oxidizable and residual state increased, especially the oxidizable state. Sediment disturbance significantly increased the release of Cu and Pb.(3) The results of static release experiments indicated that adding apatite and zero valent iron as composite additives had better inhibiting effect for Cu and Pb, it decreased the release of heavy metal significantly. In addition, compared with the addition of apatite alone, adding zero valent iron increased the pH value of water, and significantly reduced the Eh values of sediment, and it could also reduce total phosphorus in water effectively and had less impact on the content of the total Fe of the water. Compared with the control group, the fraction of Cu and Pb in the sediment with apatite and zero valent iron as composite additives transferred from acid exchangeable state which have high biological effectiveness to reducible, oxidizable and residual state which have low bioavailability in the 45 days. And the inhibiting effect increased with increasing doses of zero-valent iron.