| Soil contamination of heavy metals has become an increasingly important environmental issue in Northeast of China. Investigation of sorption phenomena of heavy metals and potential effects by other coexistence pollutants in combined pollution is of great importance, because these processes are associated with the mobility, bioavailability, bioaccumulation, and finally the fate of heavy metal pollutants in the soil environment. The further understanding of the interaction mechanism between other coexistent organic compound and heavy metals will help us to apprehend and evaluate the complex behaviors and ecological risks of heavy metals in the actual environment, and will offer scientific basis for regulation, control, and remediation of inorganic pollutants in the Northeast of China where heavy metals often co-exist with other pollutants.Based on the sorption of Pb2+, Cu2+and Zn2+to soil-water interface, the sorption mechanisms of Pb+and Cu2+in combined pollution environment were discussed detailedly, including many factors which influence the sorption process. In addition, Sorption behavior of Cu2+was attributed to mineral composition and organic matter in soil. Besides, the sorption processes and interaction effects of Cu2+in other co-exiting pesticides were investigated. The main conclusions of this dissertation are as follows:(1) Batch experiments were conducted to investigate the sorption characteristics of Pb2+, Cu2+and Zn2+by soil and main factors influendcing sorption effect were examined.The sorption isotherms of three metals were well reproduced using the Freundlich model. Sorption coefficients for heavy metals were depended on soil pH content, organic carbon, cation-exchange capacity (CEC) and free iron oxide (Ald). The pH and ionic strength of soil solution were two primary parameters for influence on sorption of heavy metals. Sorption amount of metal and sorption coefficients (KF) increased with the increase of pH and the decrease of ionic strength. The sorption of Pb2+, Cu2+, and Zn2+on soil was exothermic and spontaneous.(2) The behavior of Cu2+in untreated samples and soil samples treated with hydrogen peroxide to remove organic matter in the soil was compared. The results showed that there were obvious changes in the physico-chemical properties of the soil which was removed of organic matter. Soil organic matter was response to the sorption of Cu2+on soil and dissolved organic carbon could facilitate the mobility of the metal, and the Cu2+sorption of the samples treated depressed. The adsorption data were fitted well by the Freundlich equation and the Langmuir equation. Multiple regression analyses of the sorption isotherm parameters and soil physico-chemical properties suggested that pH2O accounted for about84.5%of the variance in the Freundlich pre-exponential parameter (XF) of original soil, and CEC and organic carbon (OC) accounted for65.4%of the variance in the Freundlich exponent(n); KF of treated soil was independent of soil properties and CEC accounted for only65.4%of n of treated soil; the Langmuir coefficient (Qmax) of original soil was linear with OC, Ald and CEC, but after soil treated, Qmax was remarkably dependent of CEC.(3) The competitive sorption and desorption of Pb2+and Cu2+in soil were investigated using single and binary metal solutions. The desorption isotherms of Cu2+and Pb2+were similar to the sorption isotherms, with well fit of Freundlich equation (R2>0.96). The results showed that the soils had greater sorption capacity for Pb2+than Cu2+in single and binary metal solutions, which was affected strongly by the soil characteristics. In the binary metal solution containing Pb2+and Cu2+(1:1molar ratio), the amout of Pb2+and Cu2+sorption was affected by the simultaneous presence of the two metals, indicating the competition between the two metals. The results of Fourier transform infrared (FT-IR) spectroscopy revealed that the carboxyl, hydroxyl and carbonyl groups were the main binding sites of metal ions.(4) The effects of thifensulfuron (TS),2,4-dichlorophenoxyacetic acid (2,4-D), and atrazine (AT) on the sorption of Cu2+on soil were investigated. The results indicated that thifensulfuron and2,4-D markedly diminished the sorption of Cu2+Mechanisms of the suppression effects of thifensulfuron and2,4-D on the Cu2+sorption included the following:the degrease of equilibrium solutionl pH and soil zeta potential simultaneity occurred in the presence of thifensulfuron and2,4-D, the increase of equilibrium solutionl DOC, the DOC-Cu, TS-Cu and2,4-D-Cu complexes had the weaker affinity than Cu2+ion itself, hence decreased the sorption of Cu2+. The presence of AT significantly increased Cu2+sorption, which could be due to increasing Cu2+sorption via the atrazine bridge, or due to the increase of equilibrium solutionl pH and the decrease of equilibrium solutionl DOC. The above results provide data to predict and model the environmrntal health and ecological risk of heavy metals, improve the understanding of sorption mechanisms of pulltants in combined contamination, and offer a theoretical gist for the sorption of inorganic pollutants in pesticide-contaminated soil. |
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