Sorption And Disorption Behaviors Of Copper, Cadmium And Phosphate On Marine Sediments

The concentrations of heavy metals and nutrient elements are important for the marine environmental quality. Phosphorus is one of the main elements that can lead to eutrophication, red tide and other nutritional phenomena. Some heavy metals (such as copper, cadmium) may produce toxicity on organisms if they are excessive, and will ultimately affect human health through enrichment and transfer in the food chain. Sediment/seawater interface is the main place for exchange and reaction of various pollutants. Natural sediment colloids affect the environment behaviors of the pollutants through a series of physical and chemical reactions, such as adsorption, complexation, coprecipitation, etc. As an important process of heavy metals and phosphorus biogeochemical cycling, the migration and transformation of heavy metals (copper, cadmium) and phosphorus on marine sediments and their interactions are of great significance.In this thesis, the sorption and desorption behaviors of Cu2+, Cd2+, PO43+on sediments sampled from Jiaozhou Bay, maricultural area of Rongcheng and Changjiang Estuary were studied through laboratory experiments. The effects of surface charge properties of sediments, environmental factors such as temperature, salinity were discussed. The combined sorption behaviors among Cu2+, Cd2+, and PO43-were also investigated. The main conclusions are as follows,(1) The acid-base titration results showed that with pH increasing from3to10, the sorption density of proton on the surface changed from positive to negative. The points of zero net proton charge (pHPZNPC) of the sediments were between4.0and4.5. The sorption kinetics process of Cu2+(0～200mg·L-1) with high concentration level could be well described by pseudo-second-order kinetic rate equation and Elovich equation. The media affected the sorption rate, which increased by the order of artificial seawater (ASW), diluted seawater(DASW), distilled water(DW). The sorption isotherms could be described by Langmuir isotherm. Estimation of thermodynamic parameters indicated that the sorption of Cu2+was spontaneous (△Gθ<0) and endothermic (△Hθ<0) with an increase in the degree of freedom (△Sθ<0). The sediment with lower pHPZNPC and higher Hs could adsorb more copper. The sorption capabilities were different in different medium, which increased by the order of DW, ASW, DASW.(2) The surface negative charges of sediment sampled from Changjiang Estuary were higher under lower salinity condition (from NSW to1/4NSW). The sorption and desorption kinetic processes of Cu2+(0～2mg·L-1), Cd2+(0～1.2mg·L-1) with low concentration levels could be well described by pseudo-second-order kinetic rate equation and Elovich equation. The sorption and desorption isotherms of Cu2+, Cd2+could be described by Freundlich isotherm. The sorption capabilities of Cu2+were increased with the decreasing of salinity and increasing of temperature. The sorption capabilities of Cd2+were increased with the decreasing of salinity, temperature and particle sizes, and the order of sorption capabilities on the sediment through different treatment was H2O treatment>H2O2treatment> HCl treatment. The sorption and desorption kinetics process of PO43-(0～1mg·L-1) could be well described by Elovich equation and two-pools first-order kinetic rate equation. The sorption and desorption isotherms of PO43-(0～2mg·L-1) could be described by Modified Langmuir equation, and for PO43-(0～16mg·L-1) Langmuir equation was appropriate. The sorption capabilities of PO43-were increased with the decreasing of salinity, while desorption capabilities changed contrariwise.(3) The combined sorption kinetics of Cu2+, Cd2+or PO43-could be described by pseudo-second-order kinetic rate equation and Elovich equation. The sorption of PO43-was accelerated remarkably with the addition of Cu2+and Cd2+, while there was no obvious effect of the addition of PO43-on the sorption rate of Cd2+. The sorption capabilities of PO43-and Cd2+were both increased with the addition of Cu2+, Cd2+or PO43-. The isotherms of the combined sorption among Cu2+, Cd2+, and PO43-were proved to follow Freundlich equation. The sorption capabilities were promoted and the desorption one was inhibited for Cu2+, Cd2+and PO43-in the combined system.(4) The amounts of surface charge of the sediments sampled from East China Sea and maricultural area of Rongcheng were affected by sampling site, sediment composition, particle size, etc. The modified point of zero charge (PZC) were about6.1. The adsorption isotherms of PO43-(0～1.6mg·L-1) onto all the samples could be well described by Modified Langmuir equation, and the EPCo was between0.04and0.20mg·L-1, NAP was between0.001and0.030mg·L-1. The surface charges and sorption capabilities of suspended matters were higher than sediments. The surface properties and sorption capabilities of sediments sampled from maricultural area varied evidently with seasons. The sorption capabilities were affected by surface site, surface charge and specific surface. For East China Sea, there existed significant difference for the specific surface of the sediments obtained from different sampling site, and the sorption capabilities were affected by mineral composition and specific surface.