| Because the tea plant is known to be a typical aluminum accumulator,it contains high level of aluminum in its leaves, but whether or not the aluminum of leaves threating to human health has not been determined, therefore, studying the environmental behavior of aluminum in tea plantation soil is particularly important. By way of takeing the Mengshan tea plantation soils as the research materials, using batch method and oscillation equilibrium method, the pape researched the adsorption-desorption kinetic characteristics and thermodynamic characteristics of aluminum by the raw soils and particle-sized fractions,and analyzed the influence of organic matter and free iron oxide, in order to understand the characteristics of tea plantation soil and environmental behavior of migration transformation about aluminum in tea plantation soil,thus provideing the theoretical reference for how to manage the tea plantation soil, to decrease the aluminum content in tea and reduce the possibility of inhaling of excessive amount of aluminum by tea drinking for the people based on the premise that the quality and production of tea do not be influenced.The main results were as followed:(1) The equilibrium time of adsorption of two kinds of soil, containing riginal soils and particle-sized fractions,was240min, and the reaction of adsorption can be divided into two types:a fast reaction and a slow reaction, which explainded that there were electrostatic adsorption and specific adsorption in the soils.Adsorption speed was significantly correlated with the content of organic matter, free iron oxide and CEC, which showed that increasing of content of organic matter, free iron oxide and CEC, brought about rise of adsorption speed at the beginning, meanwhile,ultimate adsorption capacity also increased therefore, the adsorption capacity depended on the fast reaction. The reaction of desorption was more slowly and complicatedly than the the reaction of adsorption. Although there were different desorption characteristics among the particle-sized fractions, all the soils could reach the desorption equilibrium in720min. Meanwhile,desorption speed was not related to the physicochemical properties of soils, which explainded that in addition to the physicochemical properties of soil,there were other factors related to the desorption speed of aluminum by soils. According to the fitted results of using the kinetic equation, Elovich equation was the most suitable equation for describing the the reaction of adsorption, at the same time, Elovich equation and Double-constant equation both were the most suitable equation for describing the reaction of desorption, which showed adsorption-desorption process were not simple and reversible, but were complex process related with affinity for aluminum of the soil surface.(2) Increasing of concentration of aluminum ions,brought about rise of adsorption capacity of riginal soils and particle-sized fractions in the reaction of isothermal adsorption,but there were differences among particle-sized fractions of soil about adsorption capacity. The results showed that the adsorption capacity of clay was the largest in two kinds of soils, meanwhile, the adsorption capacity of raw soils and particle-sized fractions of purple soil followed the order:clay>silt> fine sand>raw soil>coarse sand,which were consistent with the content of organic matter, free iron oxide and CEC; the adsorption capacity of raw soils and particle-sized fractions of yellow soil followed the order:clay>silt> raw soil> fine sand>coarse sand,besides coarse sand and fine sand influenced by surface area, the adsorption capacity of raw soils and the rest of the particle-sized fractions also were consistent with the physicochemical properties of soil. According to the fitted results of using the isothermal adsorption equation, the adsorption of aluminum by raw soils and particle-sized fractions of purple soil fitted well to the Freundlich equation, while the adsorption of aluminum by the the raw soils and particle-sized fractions of yellow soil fitted well to the Langmuir equation. In the reaction of isothermal desorption,the desorption rate of raw soils and particle-sized fractions of purple soil followed the order:coarse sand>raw soil>fine sand>silt>clay; and the desorption rate of raw soils and particle-sized fractions of yellow soil followed the order: fine sand> coarse sand> raw soil> silt>clay,these orders were contrary to the content of organic matter and free iron oxide of soil,the rate of specific adsorption increased with the increase of the content of organic matter and free iron oxide of soils, thereby, the desorption rate decreased,which showed that the retention capacity of aluminum by raw soils and particle-sized fractions was due to the organic matter and free iron oxide of soils,in turn, the activity of aluminum in the tea plantation soils was influenced. (3)The electrostatic adsorption capacity increased after removal of organic matter, free iron oxide respectively,meanwhile,there was specific adsorption of aluminum by organic matter and free iron oxide,so decreasing of organic matter and free iron oxide,bought of rise of desorption rate. According to the fitted results of using the isothermal adsorption equation, the adsorption of aluminum by raw soils and particle-sized fractions of purple soil which were removed organic matter, free iron oxide respectively also fitted well to the Freundlich equation, while the adsorption of aluminum by the the raw soils and particle-sized fractions of yellow soil which were removed organic matter, free iron oxide respectively fitted well to the Langmuir equation as before.Therefore, organic matter and free iron oxide were the main carrier of specific adsorption for aluminum in tea plantation soils,whose content was consistent with the retention capacity of aluminum by soils, the activity of aluminum,and the content of activated aluminium absorbed by tea tree form the soils. In the management of tea plantation soils,the soil can be improved properly,according to the aluminium content required by the growth of tea tree, in order to enhance the retention capacity of aluminum by soils, thus,reduce the activity of aluminum and the content of tea leaves. |
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