Study On Physicochemical Characteristics And Phosphate Adsorption Behaviors Of Sediments From The Yellow River

As a high-silt river, a large number of silt particles in the Yellow River played an important role in the adsorption of water pollutants. In this thesis, the sediment samples were collected from 6 cross-sections through the desilting basin of Queshan reservoir, and the relationship among the characteristic parameters of their physicochemical properties was determined. The adsorption and desorption process of phosphate on sediment (B1 and B2) was conducted to analyze the corresponding dynamic process, isotherms, influence factors, reversibility and structural variation. Moreover, the adsorption mechanism was identified with some specific surface analysis techniques. The results listed as following:The neutral or slight alkaline sediment particles were mainly composed of clay, silt and fine sand, with very low content of organic matters and some negative charges on their surface, then low flocculating ability was observed among these sediment particles. There were good correlations existed among these physicochemical parameters characterizing these sediments. The surface of sediment particles showed complex morphology and heterogeneous pore size distribution, being mainly composed of mesopore. The pore surface fractal dimensions (Ds) of these sediment particles were 2.67-2.89, which implied a highly filling capability on the surface of these particles. The pore-size distribution also presented certain contribution to above Ds values. In addition, the complex surface morphology of these particles had strong influence on the surface element distribution, which could lead to the heterogeneity of surface adsorption sites.The adsorption process could be divided into two stages:a high-speed physical adsorption and physicochemical adsorption (0-3h) stage, slow-speed chemical sorption. A pseudo second-order reaction kinetic equation fitted above dynamic process. The curves of adsorption isotherms did not pass the origin of coordinates which was divided into two parts by the zero equilibrium P concentration (0.038-0.049mg-L-1). The Langmuir cross-axis-type adsorption model showed much better fitting results for above mentioned phosphate adsorption curves than other adsorption models. Moreover, phosphate adsorption onto sediment particles was an endothermic process, and showed a solid concentration effect, particle size of sediments, pH value, salinity and organic matter content of adsorption solution matrix had important influences on the above mentioned adsorption process. In addition, phosphate adsorption onto sediment particles had reversibility, and phosphate desorption could occurr under some specific conditions.Once phosphate was absorbed onto the sediment particles, their specific surface area, pore volume and pore distribution were slightly decreased, but average pore diameter was slightly increased. The change in pore volume within pore size of 1.5-30nm was significant. It was observed that lots of phosphate absorbed on the sediment surface of ridge, concave and saddle areas, which occupied more than 96% adsorption capacity. In addition, it can be deduced that Al, Fe, Ca hydrous oxides were a main component in phosphate adsorption.