Study On The Grain Size Effect Of Heavy Metals In The Sediments In The Yellow River In Baotou

As is known to all, sediments are the source and convergence of contaminants including heavy metals in water environment. The transportation and transformation, ultimate location as well as the secondary pollution of heavy metals in water environment have close affinity with the grain size, specific surface of sediments, and the content of some active components like CEC and carbonate, ferrimanganic oxide, organic matter. Therefore, it is necessary to carry out a close research on the grain size distribution characters of sediments and the species characters of heavy metals at different grain size levels, probe into the grain size effect of sediments upon the adsorption and release and species distribution of heavy metals and take into consideration the basic physicochemical properties of different grain size components before the law of transportation and transformation of heavy metals in water environment can be correctly elucidated and the potential harm of heavy metals in sediments can be comprehensively and objectively assessed.In view of the fact that the Yellow River in Baotou is a typical and representative section contaminated by heavy metals along the catchments of the whole river, in this thesis, an experimental research on the species distribution of heavy metals within different grain sized sediments, based on the extraction of sediments in the main stream and tributaries of the Yellow River, is for the first time carried out. In this research, the grain size effect of heavy metals in the sediments is discussed, the relation between the grain size effect and the physicochemical properties of sediments such as grain size and specific surface, as well as the content of CEC and carbonate, ferrimanganic oxides. At the same time the adsorption and release characteristics of heavy metals by different grain sized components are also studied. All these researches aim at providing scientific foundation for assessing the study on the transportation and transformation mechanism of heavy metals in the water-sediments system of the Yellow River as well as the contamination degree of heavy metals, and providing some references for assessing the ecological harm brought by heavy metals in the water-sediments system. The conclusions drawn from the research are as follows:1. The bound state of ferrimanganic oxide is the leading species of non-steady-state heavy metals like Cu, Pb and Zn in various sized sediments in the main stream of the Yellow River. The bound state of organic matter and ferrimanganic oxide are respectively the leading species of Cu, Pb, and Zn in various sized sediments in the tributaries.Besides, the different mass fractions of various sized sediments bring about different contribution ratio of different sized sediments in the species distribution of heavy metals. For an impartial assessment of heavy metals' potential harm, both the species content anddistribution and the effect of various sized particles' mass fractions should be taken into consideration.2. The grain size effect is the result of interaction of some active components like organic matter, carbonate, ferrimanganic oxides etc. with the grain size of sediments playing the master control role. The species content and total amount of the three heavy metals—Cu, Pb, Zn—in the sediments in the Yellow River all manifest the tendency of decreasing with the rising of the grain size, revealing "the law of the grain size control". Sediments show a highly consistent effect on the total amount of elements and various extraction species. While the content of Carbonate and Ferro oxide is the main factor affecting the species distribution characters of heavy metals in sediments of the Yellow River in Baotou. Correspondingly, the non-steady heavy metals in various sized sediments all take the ferromanganic oxides as their leading species and the carbonates as the secondary.The experiments in the research furthermore discover that the content of Zn (IV) rises slowly as the grain size increases, showing the characteristic of a "negative grain size effect". This reason of this phenomenon needs further research.3. Within the same initial concentration, surficial deposits of the Yellow River with varied grain sized components manifest apparently the law of grain size effect in adsorbing the Cd2+—the adsorption rate decreases with the increase of the initial temperature. The bigger the grain size is, the faster the decrease of adsorption rate is and the more effect pH value shows on the adsorption process. Besides, the adsorption process is also influenced by the pH value. In contrast, the Freundlich equation can more effectively fit the isothermal adsorption process on Cd2+ by the five grain-sized particles. Taking no account of the interaction among the various sized components, the adsorption contribution ratio at the two grain-sized levels—Dl and D2 obviously rises with the rising temperature, while that of D3 and D4 apparently decreases and D5 contributes most. Apart from those discoveries, the experiments also findthe primary order of release capacity of Cd2+ ------D5? D4>D3>D2^D1. With all theexperimental results taken into account, the inverse proportion between the sediments' adsorption capacity and release capacity on heavy metals can be generalized.