| Sediment is the important reservoirs of silicon in rivers,and its“source”or“sink”effects on nutrient silicon in overlying water which plays an important role in the geochemical cycle of the entire river ecosystem,this study has an important significance for the occurrence form,migration and transformation of silicon in water.The Inner Mongolia reach of the Yellow River has a special geographical location,Ulanbu Desert and Kubuqi Desert distributed over the west bank and the south bank,respectively.There are three dams in the territory,and the concentration of total particle varied greatly,human activities are frequent and the impact is complex.So,in order to reveal the water sediment is the"source"or"sink"of silicon and judge the release risk,this paper studied the occurrence form of silicon in the overlying water and sediment,the kinetics and thermodynamic characteristics of the adsorption of silicon by the sediment,and the morphology changes of silicon before or after adsorption and release,fit the data of modified Langmuir cross-adsorption isotherm.Research indicates:?1?The concentration of DSi,BSi and TSi in the overlying water are 22.26-121.06?mol·L-1,2.55-13.61?mol·L-11 and 24.80-134.67?mol·L-1in the Inner Mongolia reach of the Yellow River,respectively.DSi is the main factor for TSi;the concentration of?Si in sediment is26.34-69.66g·kg-1,and the concentration of various silicon is Residual-Si>IMOF-Si>OSF-Si>CF-Si>IEF-Si.The percentage of Residual-Si concentration to?Si is 91.78%-98.06%which is the main form in the sediment.?2?The adsorption of silicon in sediment reached the adsorption equilibrium at 24 h basically,the adsorption process is consistent with the Lagergren secondary adsorption kinetic model,and the diffusion process can be described by Weber-Morris;the adsorption capacity of sediment to silicon will increase with the decrease of the sediment concentration and increase of the initial concentration of silicon;the adsorption capacity of sediment is close to the maximum when the pH is 8-9.?3?The adsorption thermodynamic behavior of silicon to the Inner Mongolia reach of the Yellow River is consistent with the revised Langmuir cross-type adsorption isotherm.The adsorption capacity of the sediment is 122.894-387.602mg·kg-1,and the concentration of NAS is47.503-268.315mg·kg-1;H1,H2,H6,H7 and H8 in the Inner Mongolia reach of the Yellow River showed the“source”of silicon in the water,H3,H4 and H5 showed a“sink”of silicon in the water.?4?The release of endogenous silicon,exogenous silicon and endogenous silicon in the sediments in the Inner Mongolia reach of the Yellow River are characterized by three stages:rapid release,slow release and more slower release.The release included other forms silicon besides IEF-Si.?5?The change of IEF-Si concentration after the sediment adsorbed silicon indicates that the sediment in the Inner Mongolia reach of the Yellow River plays a major role which is silicon source in the water body;When the adsorption capacity of silicon adsorbed by the sediment is close to saturation,CF-Si,IMOF-Si and OSF-Si in the sediments with close sampling points showed similar changes;the morphological changes after release showed that the release of IEF-Si came from exogenous silicon basically,IEF-Si and CF-Si had a potential release risk. |
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