The Phosphorus Adsorption Rule And Surface Micro-topography Change Of Sediment Particle

One of the consequences of rapid economic development in China over the past twenty years has been a significant increase in aquatic pollution. There is a large amount of sediment transported in natural aquatic systems, especially in China's big rivers. Sediment particles, therefore, play an important role in the migration and transformation of pollutants. The adsorption of nitrogen, phosphorous and other pollutants on sediment particles changes not only the concentration of pollutants in the water but also the surface micro-topography and transportation characteristics of the sediment particles themselves. More and better research into the interaction between sediments and pollutants is the key to solving these pollution problems.This dissertation discusses on a microscopic level the adsorption law of phosphorus and the changes that phosphorus produces on sediment particle surfaces. The methods and results are as follows.The study used an advanced scanning electron microscope (SEM) to observe the surface micro-topography of sediment particles. From the investigation, it was discovered that the surfaces of natural particles are very complex. Often they are heavily coated with pollutants. These polluted surfaces show notable differences compared to clean particles.In order to compare the surfaces of clean particles to polluted particles, the study performed some laboratory experiments using KH2PO4 solution as the adsorbent. Then a series of adsorption experiments were conducted on sediments with various degrees of initial phosphorus. The sediment particle surface pores which have adsorbed phosphorous iron were measured using the gas adsorption method. Based on our experiments, the study discovered that pores ranging in size from 1 to 10nm show significant changes after the particles are polluted. As the pollution levels increase, the specific particle surface area and pore volume decrease and the average pore size inversely increases. Small sized pores, it was found, gradually filled as the sediments were polluted. We used an energy dispersion spectrometer (EDS) to analyze the chemical elements on the particle surface. The statistical results of our analysis indicate a close causal relationship between the phosphorus distribution on the particle surface and its micro-topography.There are two complementary processes at work in the adsorption of phosphorous iron on particle surfaces—physical adsorption and chemical adsorption. Physical adsorption is a reversible process which occurs rapidly, whereas chemical adsorption is an irreversible process which occurs slowly. As an effect of constant flow shear stress, the phosphorous iron that is stably adsorbed on the particle surface combined with the particle surface through a chemical reaction. Where the flow shear stress is lower, pollutants, therefore, gather in pores as the reaction reached equilibrium. This gathering action causes the pores to fill.Based on our SEM observations, we used mathematical methods to describe the form and texture of the clean surface particles. From these mathematically derived results, we built a research platform. This platform calculated not only the three dimensional topography of sediment particles but also the interaction processes between the particle surface micro-area and the phosphorous iron. Combining this platform and the adsorption kinetics equations, we were able to refine an existent one dimensional numerical model for water, sediment and water quality by adding modules to it to make it more powerful and to improve its predictive accuracy. The study applied the model to simulate pollutant migration and sediment transportation respectively in the Beiyun River and the Yantan Reservoir. We were able to obtain verifiable results using this model and methodology. This model demonstrated strong potential for describing the pollution processes which contaminate clean sediments in China's river systems.