Kinetics of Specific and Non-Specific Copper Sorption on Aggregates of an Acidic Paddy Soil from the Taihu Lake Region in East China

The Taihu Lake region in East China has become prone to soil acidification, which changes heavy metals such as copper（Cu） in soil into water-soluble species and increases the mobility and contamination risks of heavy metals in the biological environment. In this study, the kinetics of Cu^2＋sorption by the bulk soil and the aggregate size fractions of an acidic paddy soil collected from the Taihu Lake region, the effects of temperature on Cu^2＋sorption, and the p H changes of the solution were investigated by static sorption and magnetic stirring. The aggregate size fractions were prepared by low-energy ultrasonic dispersing and freeze-drying. The total sorption amounts of the bulk soil and the aggregate size fractions for Cu^2＋followed a descending order of clay 〉 coarse sand 〉 bulk soil 〉 silt〉 sand, corresponding to those of organic matter content, free iron oxide content, free aluminum oxide content, and cation exchange capacity. The kinetic sorption curves of Cu^2＋by the bulk soil and the aggregates, which were divided into two stages（rapid and slow sequentially）, were well fitted by the first-order equation, the diffusion equation, and the Elovich equation, showing significant correlations（P 〈 0.05）. Specific and non-specific sorption dominated in the fast and slow stages, respectively, and the former was predominant throughout the sorption process. The specific sorption accelerated and the non-specific sorption decelerated with rising temperature. The p H of the solution decreased significantly during the specific sorption and remained unchanged or increased slightly during the non-specific sorption. When the specific sorption terminated, the p H of the solution was minimized nearly simultaneously.The sorption progress of Cu^2＋by the bulk soil significantly preceded that by the aggregates. Therefore, heavy metal contamination may be another factor reducing soil p H and metal sorption forms should be taken into consideration in studies of mitigating soil heavy metal pollution or determining environmental capacity of heavy metal in soil.