Mechanism and kinetics of aluminum dissolution during copper sorption by acidity paddy soil in South China

Abstract

Soil aggregates were prepared from a bulk soil collected from paddy soil in the Taihu Lake region and aluminum (Al) dissolution, solution pH changes during copper (Cu2+) sorption were investigated with static sorption and magnetic stirring. Kinetics of Cu2+ sorption and Al dissolution were also studied by magnetic stirring method. No Al dissolution was observed until Cu2+ sorption was greater than a certain value, which was 632, 450, 601 and 674mg/kg for sand, clay, silt, and coarse silt fractions, respectively. Aluminum dissolution increased with increasing Cu2+ sorption and decreasing solution pH. An amount of dissolved Al showed a significant positive correlation with non-specific sorption of Cu2+ (R2>0.97), and it was still good under different pH values (R2>0.95). Copper sorption significantly decreased solution pH. The magnitude of solution pH decline increased as Cu2+ sorption and Al dissolution increased. The sand and clay fraction had a less Al dissolution and pH drop due to the higher ferric oxide, Al oxide and organic matter contents. After sorption reaction for half an hour, the Cu2+ sorption progress reached more than 90% while the Al dissolution progress was only 40%, and lagged behind the Cu2+ sorption. It indicated that aluminum dissolution is associated with non-specific sorption.