| Reactions at the mineral-water interface play an important role in the cycling of matter in aquatic systems and even at the Earth's surface as well as the geochemical processes of elements,and are of significance to the environment. Kaolinite,as the most important clay mineral in soils and sediments and a main component of suspended particles in atmosphere and aquatic systems,controls the transport,fate and bioavailability of inorganic ions and organic molecules in atmosphere,aquatic systems and sediments vitally. Focusing on the reactions at the mineral-water interface,this dissertation at first gave a brief review of the theoretical basis and models of the reactions,and then investigated the surface acid-base properties of kaolinite and metal ions adsorption behavior with single- and double-site nonelectrostaic modeling (NEM). It discussed desorption kinetics of metal ions on kaolinite surface as well. Finally,this paper investigated the compositions,contaminative situations,speciation and release of heavy metals in contaminated sediments from Guangzhou water body.This work was supported by the National Natural Science Foundation of China (No. 49773206) and the Natural Science Foundation of Guangdong Province (No. 960504).Conclusions of this work were drawn as follows:(1) The proton adsorption on kaolinite under different pH conditions was described with single- and double-site NEM. And the model parameters got by nonlinear fit based on the acid-base titration data were as follows:the total surface site density and protonation constants fitted by single-site model were Nt = 4x 10"5 mol/g,pKal=2.75,pKj=5.52,and analogously NiM = 2.8x 10 4mol/g,7V,si = 3.0x 10 5 mol/g,pAal A,=1.78,pAa2A=8.47,pKa2K=5.12 by double-site model. The goodness of fit of double-site model was better than that of the single-site one.(2) The surface species of kaolinite varied as pH changed in solution. In single-site model,positive and negative charges could be attributed to the protonation and deprotonation of the single site>SOH. In double-site model,the positive charge was resulted from the protonation of >A1OH only,and had nothing to do with >SiOH. AspH<4.0,the surface Al sites and overall surface of kaolinite were positively charged. The negative charge was resulted from the dcprolonation of both >A1OH and >SiOI 1. The Al and Si sites were negatively charged as pH>6.2 and pH>4.0 respectively.(3) The adsorption amount of Pb and Cu on kaolinite increased with a rise of pH. A slow increase in the range of pH<4 and a more rapid increase in the range of pH>4 were observed. In a manner analogous to proton adsorption,metal ions adsorption was described by NEM,and nonlinear fit results indicated that both free aquo metal ions and monohydroxo-metal complexes could react with kaolinite surface and the complexation constants of hydoxo complexes were greater than those of free aquo metal ions.(4) With pH in solution increasing,fraction of soluble metal species in the system went down and adsorbed species went up. The predominant species on kaolinite surface was >SOMe at pH<-5.5,and >SOMeOM at pH>-5.5. EPR further confirmed the existence of two adsorbed species.(5) Similar to the adsorption kinetics,the desorption kinetics of metal ions from kaolinite showed a biphasic type behavior,that is,an initial fast release was followed by a slow release. And the adsorption and desorption process were not totally reversible.(6) The study results of sediments from Guangzhou water body showed that the main crystalline minerals in sediments were quartz,kaolinite and hydromica,and heavy metals (Pb,Zn,Cu,Ni,Cr,Mn) were associated mainly with residual phase,organic phase and iron oxides phase. The affinity of solid components in sediments to heavy metal ions was as follows:amorphous manganese oxide carbonate >iron oxides >organic matter,whereas the enriching amount of the latter two was larger than that of the former two.(7) Heavy metals resided in sediments were not stable at all as media condition changed in solution. They...
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