Cadmium adsorption-desorption of brown soil with freeze-thaw cycles in northeast China

Adsorption-desorption characteristics of cadmium by brown soil, a typical soil in north-eastern China, were studied under different freeze-thaw cycles by using equilibrium adsorption isotherms. Freeze-thaw cycles were represented by temperatures of -30 degrees C and 30 degrees C, respectively. Both freezing and thawing conditions were implemented for three days each and the number of freeze-thaw cycles examined was zero, one, three and six. The results showed that the amount of adsorbed cadmium for one, three and six freeze-thaw cycles was 84, 74 and 70%, respectively, compared to soil experiencing no freeze-thaw cycles. About 33.1-50.0% of adsorbed Cd was desorbed from the soil without freeze-thaw cycles, while 32.1-73.0% of adsorbed Cd was desorbed from the freeze-thaw soil at the same initial concentration of Cd; the more the frequency of freeze-thaw, the higher the Cd desorbed.