Effect Of Soil Components On Copper And Zinc Sorption-desorption Behavior By Microaggregates From Paddy Soil In Mingshan River Watershed

The typical paddy soil, collected from the Mingshan River was used to investigate the characteristics and effect of soil components which consists of organic matter, free oxide iron and amorphous oxide iron on sorption-desorption of copper and zinc by microaggregates from paddy soil by using simulation-incubation test and selective dissolution method.The results showed that whether or not remove the paddy soil components, the sorption of copper by the bulk soil and microaggregates fitted well to the Langmuir Isotherm model, while the sorption of zinc by the bulk soil and microaggregates fitted well to the Freundlich Isotherm model. These results explained the sorption of copper was monolayer adsorption while the sorption of zinc was multilayer adsorption by the bulk soil and micro aggregates from paddy soil in this research. The order of copper and zinc s sorption capacity was as follows:less than 0.002mm>2-0.25mm>bulk soil>0.053-0.002mm>0.25-0.053mm, and the sorption and retentin ability of copper was significantly greater than zinc by bulk soil and microaggregates.The sorption capacity of bulk soil and microaggregates was well correlated with the content of organic matter, free oxide iron, amorphous oxide iron, cation exchange capacity.The sorption of copper and zinc by bulk soil and microaggregates in 0.002mm and 2-0.25mm was more bigger than other particle sizes, the 0.002mm and 2-0.25mm particle size were the enrich ment microaggregates. The adsorption of copper and zinc by bulk soil and microaggregates was based mainly on specific adsorption in different concentration, moreover the percentage of non-specific adsorption of zinc was higher than copper.The sorption and retentin ability of copper and zinc by bulk soil and microaggregates were decreased in some extent after removal of organic matter, free oxide iron and amorphous oxide iron, especially the decrease was achieved the most in less than 0.002mm, the lowest in 0.25-0.053mm, the decrease caused by bulk soil and 0.053-0.002mm was between the different particles. The decrease of copper and zinc's sorption by bulk soil and microaggregates after removal of soil components in the order:that removing O.M> that removing free oxide iron>that removing amorphous oxide iron, which showed a significant difference among different treatments. Meanwhile, the results showed that the effect of organic matter was the most in adsorption, the selective adsorption of copper by organic matter was higher than zinc, the selective adsorption of zinc by free oxide iron was higher than copper, the selective adsorption ability between copper and zinc by amorphous oxide iron was no significant difference. The percentage of specific adsorption was decreased in some extent with the significant increase of non-specific of copper and zinc by bulk soil and microaggregates after removal of soil components. These results showed that the retentin ability of copper and zinc by bulk soil and microaggregates was all decreased after removal of soil components, copper and zinc was remained in soil with easy desorption in higher activity, and the mobility of copper and zinc in soil was increased with the increase of migration. The retention and buffer capacity of copper and zinc by bulk soil and microaggregates was decreased along with the decrease of percentage in specific adsorption., at the same time, the decrease of specific adsorption suggested the significant contribution of organic matter, free oxide iron and amorphous oxide iron in specific sorption.