| With the development of industry,agriculture and transportation,heavy metal pollution has become more and more serious.Sediments of rivers and lakes under natural conditions contain a large number of heavy metal pollutants.These pollutants will be re-released into water when under certain conditions,such as external forces,the change of overlying water environment,and the influence of the physical and chemical properties of the sediments,causing secondary pollution of water.This study takes sediments contaminated by heavy metals as the research object.A speed-adjustable multi-purpose oscillator and beakers are used to simulate external force disturbances,and simulated overlying water with different physical and chemical properties is configured.Designing single-variable experiment and orthogonal experiment,and useing intuitive analysis,Pearson correlation analysis,range analysis,variance analysis,response surface analysis and dynamic analysis,to study the influence of external force disturbance and overlying water environmental conditions on the migration and release of heavy metals in sediments,as well as the influence of the interaction of external force disturbance,p H and temperature on the migration and release of heavy metals,and to explore the rules of the migration and release of heavy metals in sediments under the interaction effects,the following conclusions are drawn:（1）External disturbance has a significant effect on the migration and release of heavy metals in sediments.The greater the intensity of the disturbance,the greater the release of heavy metals.When the perturbation frequency reaches 240r/min,the release rates of Pb and Cd are 1.02×10-4 and 1.23×10-4,respectively.In addition,the release of heavy metals has a significant positive correlation with the turbidity of the overlying water,a significant negative correlation with the concentration of heavy metals in the interstitial water,indicating that external force disturbance promotes the release of heavy metals into the water by promoting interstitial water diffusion and particle resuspension.（2）Physical and chemical factors such as p H,salinity and temperature of overlying water have significant effects on the migration and release of heavy metals in sediments.The lower the p H,the greater the release of heavy metals;the greater the salinity,the greater the release of heavy metals;the higher the temperature,the greater the release of heavy metals.When the p H is equal to 5,the maximum release rates of Pb and Cd are 6.7×10-6 and 5.3×10-6,respectively;when the salinity is 4g/L,the maximum release rates of Pb and Cd are 8.87×10-6 and 1.14,respectively×10-5;when the temperature is 30℃,the maximum release rates of Pb and Cd are 8.97×10-7and 6.65×10-7,respectively.Pearson correlation analysis showed that the correlation coefficients between the three physical and chemical factors and the release amount of Pb and Cd were all greater than 0.9,showing a significant correlation,indicating that these three overlying environmental factors could affect the migration and release of heavy metals in sediments.（3）When the external force disturbance acts together with the p H and salinity of the overlying water,the external force disturbance has the most significant impact on the release of heavy metals,followed by salinity,and p H is the least affected.In the orthogonal experiment,the range and the square sum of the mean deviation of Pb and Cd release controlled by external force disturbance factors are the largest,followed by salinity and p H.Intuitive analysis and analysis of variance show that the best conditions for the maximum release of Pb are the disturbance frequency of 240r/min,the salinity of 4g/L,and p H=6,while for Cd are the disturbance frequency of 240r/min.,the salinity of 3.5g/L,p H=6.（4）The interaction between salinity and p H is the most obvious.The results of response surface analysis show that the disturbance intensity,p H and salinity all interact with each other,but the interaction between salinity and p H is the most obvious one.In addition,the release of Pb and Cd is also affected by the interaction of disturbance intensity and p H.（5）The release process of heavy metals has the highest fitting degree with the second-order kinetic equation.Through fitting analysis,it is found that the correlation coefficient of fitting result between the release amount of Pb and Cd and the second order kinetic equation is greater than 0.98,indicating that the migration and release of heavy metals include external liquid film diffusion,surface release and intra-particle diffusion.In addition,the fitting correlation coefficient between the release of Pb and the parabolic diffusion equation is 0.9531,indicating that the Pb release process is dominated by a certain diffusion form,while the fitting correlation coefficient between Cd release and the biconstant equation is 0.9158,indicating that the affinity of the adsorption sites on the sediment surface to heavy metals is different during the release process of Cd.There are 35 figures,23 tables and 110 references in this paper. |
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