Migration Mechanism And Control Strategies Of Heavy Metals On Polluted River Sediments

With the rapid development of industrialization and urbanizaition, a large amount of industrial effluents and domestic sewage are discharged into the urban rivers, leading to the enrichment of pollutants in sediments, especially the enrichment of heavy metals, the toxicity of which will greatly endanger the living organism by various means like the food chain. In order to understand how the heavy metals from sediments of polluted rivers are emitted in natural water and what can be done to these polluted sediments, the present study, based on field sampling from four sections of Chaohu Shuangqiao River, by analysing the total amount of heavy metals in sediments and their possible emission amount, aims to make out the emission rule of heavy metals in natural water and the change of ORP and pH during the natural drying process of these heavy metals. The passivation effects of sediments modified with different bentonites are also studied.(1) The sediments of Shuangqiao River are seriously polluted by heavy metals. The content of Cr, Pb and Cu in all observation points exceeds the background values of heavy metals in Anhui Area. The possible release amount of Cr, Pb and Cu are estimated to be twice as much as the background values of heavy metals in Anhui Area.(2) At the initial stage of the sediment release experiment, the release rate of Pb keeps increasing before reaching its peak value and then gradually falls to a constant while that of Cr and Cu tends to stabilize immediately after arriving at the peak value.(3) During the natural drying process of sediment, the low oxidation state of sediment will change in 76 hours, from the original -355Mv into 110Mv. Meanwhile, the release amount of heavy metals will vary widely, especially Pb, which alters most at the fourth day. One thing to be noted, although the air leaking into the sediment will cause an increase in its ORP, which leads to the oxidation of many reducing substances, its pH is left unchanged, constant between 7.3~7.7.(4) During the water leaching experiments passivated with bentonite, as the content of bentonite increases, both the concentration of heavy metal pollutants and the concentration of heavy metals leached from the sediments gradually decreases. When the content of bentonite reaches 20%, the final release concentration of Cr, Pb and Cu undetected.