| River sediment is an important part of natural ecosystem. Throughadsorption, precipitation, complexation, biological absorption, and otherpathways heavy metals ultimately stored in the river sediments. Due to thecontinuous accumulation, contents of heavy metals in sediments is usuallyseveral orders of magnitude higher than the overlying water. When the externalenvironmental conditions change, heavy metals in sediments may havere-released into the overlying water, causing the upper overlying water heavymetal pollution. Therefore, the study of heavy metals in sediments has becomeone of the research topic.In this paper, several rivers sediments in Taiyuan City for the study,analysis the heavy metal content and form distribution and evaluated pollutionlevels. Analysis the influence factors of desorption of heavy metals, as well asheavy metals before and after desorption morphological changes andbioavailability. Through several typical desorption kinetics model of heavy metals desorption data were fit to find the best fitting model and desorptiontime-varying relationship. The main conclusions of this paper:The presence of heavy metals in the river morphology is different, butoverall, mainly heavy metals bound to organic matter and residual presence.According Nemerow pollution index classification table to northern inland riversediments background values as evaluation criteria, Huyu River and YumenRiver sediments heavy metals are severe pollution, Fen River sediments heavymetals are light pollution.EDTA on sediment Pb, Cu have better treatment effect, desorption ratesignificantly higher than the citric acid and oxalic acid; for Cr desorption rate,EDTA and citric acid is almost the same, both significantly higher than oxalicacid; three kinds of chelating treatment effect of Zn are not ideal.Heavy metals desorption rate as chelating concentration increasing, but nota positive correlation between the twoï¼›Overall desorption rate rises over timeuntil eventually stabilizeï¼›Desorption rate was affected by heavy metal speciesand species distribution of heavy metal elements.EDTA and citric acid can effectively remove sediments acid extractablesome heavy metals, Fe Mn oxide bound heavy metals also have better removal,although it can remove organic matter and residual presence heavy metal, butremoval low. Heavy metals in sediments after desorption, bioavailabilitydecreases. By orthogonal experiment method, the optimal conditions for thedesorption of heavy metals:the use of EDTA, chelating agent concentration of0.3mol/L, desorption time was480min. The degree of influence of each factoron its desorption rate descending order: chelating species> chelatorconcentration> desorption timeIn this paper dynamics model was used to fit the desorption process ofheavy metals in sediment, the model from good to bad is double constantequation> Elovich equation> a kinetic equation. Over time, the heavy metaldesorption rate decreases. |
