Effect of Yellow Soil Components on Adsorption and Desorption of Cadmium by Microaggregates in Mingshan Watershed,Sichuan Province,China

The four kinds of old alluvial yellow soil,including woodland,paddy fields,tea garden and dry land,collected from the Mingshan River,was used to investigate the effect of yellow soil components on adsorption and desorption of Cd2+ by microaggregates with isothermal adsorption method of equilibrium liquid and desorption method of NH4OAC and EDTA.The results showed that:the distribution of soil organic matter,free iron oxide and cation exchange capacity was basically the same in bulk soil and particle size of microaggregates,being the highest of yellow soil of Woodlang.The adsorbance of Cd2+ increased with the initial concentration of Cd2+ before and after removing soil components.The adsorbance was diminishing as the following sequence:(0.002 mm)2～0.25 mm bulk soil0.053～0.002 mm0.25～0.053 mm,being significantly positively correlated with OM,free iron oxides and CEC.The size relationship of adsorption reduction was the following sequence:removal of OMremoval of free iron oxide.The contribution of OM was much more than free iron oxide.The adsorption of Cd2+ in four patterns of yellow soil was exchange adsorption mainly to complexing adsorption supplemented.Freundlich equation best fitting effect adsorption isotherm reached a significant level.Before and after removing soil components adsorbance and initial concentration of Cd2+ had showed a nonlinear correlation.The equilibrium constant K was significantly positively correlated with soil organic matter,free iron oxide and cation exchange capacity.After removing soil components,K had decreased which adsorption capacity becamed smaller.The Kd was negatively correlated with initial concentration of Cd2+.NH4OAC desorption rate increased with initial concentration of Cd2+.According to the maximum of NH4OAC desorption rate,the size relationship was the following sequence:0.25～0.053 mm0.053～0.002 mmbulk soil2～0.25mm (0.002 mm),but EDTA desorption rate decreased with the increase of cadmium's initial concentration,whose decreasing regularity was contrary to NH4OAC desorption rate.After removing soil components NH4OAC desorption rate increased significantly,while EDTA desorption rate reduced.The desorption rate of tea garden and dry land decreased,which of woodland and paddy fields increased.After removing soil components,non-exclusive adsorption was significantly positively related to total adsorbance,while specific adsorption was significant negative correlated with total adsorption.