Kinetics of soil cadmium desorption under simulated acid rain

Soil acidification can result in the release of heavy metals stabilized by soil components into soil solution, and therefore it causes ecological risk. The kinetics of Cd desorption from two Chinese soils (ultisol and oxisol) distributed in the acid rain sensitive areas of southern China, were studied using a flow-stirred method under simulated acid rain conditions. Cd desorption was well described by the first-order kinetic equation. Percentages of Cd desorbed were 80–99% in ultisol and 25–28% in oxisol, respectively. Cd desorption, regarded as a heterogeneous diffusion in soils, could be also fitted by the Elovich equation. The desorption process could be divided into a fast reaction and a slow reaction, which were corresponded to the exchangeable and the specific sorbed Cd, respectively. The obtained results are essential to understand the process of heavy metal release under acid deposition conditions and to evaluate the ecological risk of acid deposition in those acid rain sensitive areas of China.