| The four kinds of old alluvial yellow soil, including woodland, paddy fields, tea garden, and dry land, collected from the Mountain Regions of Western Sichuan, was used to investigate the characteristics and effect of soil components which consists of organic matter, free oxide iron and cation exchange capacity on sorption-desorption of cadmium, in order to study regional prediction of heavy metal environmental capacity, alleviate the heavy metal pollution, optimize land to use means to provide reference. The results are as follows:(1) The distribution of soil organic matter, free iron oxide and cation exchange capacity was basically the same in the bulk soil and the particle size of microaggregates from the four kinds land uses of yellow soils, being the highest of Forest Yellow. The size relationship was diminishing as the following sequence:(<0.002mm)>2-0.25mm>buk soil>0.053-0.002mm>0.25-0.053mm. Free iron oxides, cation exchange capacity and organic matter content were significantly positively correlated.(2) The cadmium adsorbance in the bulk soil and the particle size of microaggregates from the four kinds land use of yellow soils increased with the initial concentration of Cd2+before and after removing soil components (organic matter, free iron oxide).The adsorbance was diminishing as the following sequence:(<0.002mm)>2-0.25mm>bulk soil>0.053-0.002mm>0.25-0.053mm, being are basically the same of the distribution law of soil organic matter, free iron oxide and cation exchange capacity. The size relationship of adsorption reduction was the following sequence: removal of organic matter> removal of free iron oxide. The contribution of organic matter to adsorption of Cd2+by microaggregates was much more than free iron oxide. The cadmium adsorption in four kinds of yellow soils was exchange (electrostatic) adsorption mainly to complexing (chelating) adsorption supplemented. Freundlich equation best fitting effect in the four kinds of yellow soils adsorption isotherm reached a significant level. Before and after removing soil components the cadmium adsorbance and the initial concentration of Cd2+have showed a nonlinear correlation, which the Freundlich equation’s n were all not close to1. The equilibrium constant K was significantly positively correlated with soil organic matter, free iron oxide and cation exchange capacity. After removing soil components the K decreased that the adsorption capacity becamed smaller. The variations of adsorption capacity and adsorbance were the same. The distribution coefficient Kd was the same trend with the maximum of adsorption capacity Xm and Constant K,(<0.002mm) of which was the largest. Kd was negatively correlated with initial concentration of Cd2+.(3) The desorption rate of NH4OAC and EDTA increased with the adsorbance by bulk soil and the particle size of microaggregates of the four land uses of yellow soils.The size relationship was the following sequence:(<0.002mm)>2-0.25mm>bulk soil>0.053-0.002mm>0.25-0.053mm. NH4OAC desorption rate is much greater than EDTA desorption rate. The NH4OAC desorption rate of Cd2+by bulk soil and the particle size of microaggregates increased with the initial concentration of Cd2+before and after removing soil components. According to the maximum of NH4OAC desorption rate, the size relationship was the following sequence:0.25-0.053mm>0.053-0.002mm>bulk soil>2-0.25mm>(<0.002mm), but EDTA desorption rate descreased with the increase of initial concentration of Cd2+, whose decreasing regularity was contrary to ammonium acetate desorption rate. After removing soil components NH4OAC desorption rate increased significantly, while EDTA desorption rate reduced. The desorption rate of yellow soils of tea garden and dry land decreased, which of woodland and paddy fields increased. After removing soil components, Non-exclusive adsorption of Cd2+was significantly positively related to total adsorbance, while specific adsorption was significant negative correlated with total adsorption. |
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