Research On In-Situ Capping Technology For Heavy Metals In Contaminated Sediment

Sediment is an important part of the water system of the ecological environment, is the main place for the accumulation of organic matter, nutrients and heavy metals and other pollutants. Under effectively reduce exogenous contamination, release large amounts of pollutants in sediment accumulated cause secondary pollution of the water environment. Because microbial can not be degradation heavy metals, and heavy metals in the environment can only exist in different forms and conversion to occur, so the heavy metals in sediment control becomes very difficult. As a new contaminated sediment remediation technologies, in situ capping technology for its simple, low investment, better handling, low ecological risk caused widespread concern. This thesis is the use of in-situ capping technology to inhibit the release of heavy metals in sediment, select the appropriate material for covering the heavy metals in sediment cover treatment to reduce its damage to the overlying water environment, analyze the effectiveness of different factors under cover, and try to investigate the mechanism of the cover in place.Selection of hydroxyapatite, calcite and zeolite as a covering material, experimental studies covering treatment of heavy metals Pb, As, Mn and Cr were contaminated sediment. For high and low (respectively 1.5 and 2 times the three Chinese soil environmental quality standard limit value) of two different concentrations of heavy metal contaminated sediment, calcite, zeolite of heavy metals Pb, As, Mn and Cr contaminated sediments have inhibiting the release of a certain role, hydroxyapatite As and Mn only heavy metal contaminated sediment exists a good release inhibitory effect. At high concentrations of pollution,2.5cm and 1.3cm thick sediments of zeolite As for the release of inhibition rates were 63.94% and 42.34%,800 mesh and 325 mesh calcite calcite Mn fluxes of sediment in the inhibition rate were 95.4% and 91.4%. Calcite mixed with sand overburden at high and low concentrations of contaminated sediments of different As the release of inhibition rate of up to 98.74% and 98.45%. Thus, increasing the thickness of the cover system, reducing the size of the cover material, the covering material uniformly mixed more conducive to reducing heavy metal ions Overlying water release.TCLP toxicity characteristic leaching procedure adopted for heavy metal contaminated sediments coverage evaluation. Each covering sediments of Pb, As and Mn leaching test group were lower than the blank, different cover system to some extent, promote the transformation of heavy metals from contaminated sediment leaching easy state to a stable state. By comparing the amount of coverage of different leaching materials under different conditions of heavy metals in sediment covering the way can be found, zeolite and calcite of heavy metals in the sediment covering the effects are good, calcite 3cm thick (325 mesh) mixed with sand under cover system As a minimum amount of leaching (only 1.79mg/kg), compared to the control group decreased 66.2%.Use Tessier sequential extraction method to extract sediment cover, analyze morphological changes in their heavy metal, try to cover mechanism analyzed and discussed. Mutual conversion between different levels of heavy metals in sediment under various forms of coverage, on the whole are made can be extracted and available state to the residual changes. Hydroxyapatite series reduces residual content of Cr in the sediment, sediment accelerated release of Cr Overlying water. But its release of sediment in significant inhibition of Mn, greatly reducing the available Mn content. Calcite and zeolites form transformation in sediment Pb and As the role of obvious, especially 3cm thick calcite (325 mesh) mixed with sand to increase the effective overburden sediments of Pb, As, Mn and Cr residual phase its residual than the control group increased by 4.07%,8.77%,3.32% and 5.38%.