Preliminary investigation on adsorption and desorption of Cd in soil with different reduction states

Cadmium adsorption and desorption are important processes to control its solubility and bioavailability in soils.In this study we report the adsorption and desorption of Cd under three different reduction states in a paddy soil developed from yellow brown soil.For the strongly reduced soil,the Eh and pH decreased and stabilized at-474 mV and 5.02.The percentage of adsorbed Cd was reduced from 99.96% to 94.70%.The average Cd desorption ratio was 90.01%.At the moderate reduction level,the soil Eh decreased to around-90 mV and pH increased slightly.The average percentage of adsorbed and desorbed Cd was respectively 99.96% and 66.09%.For the aerated soil there is a small change of Eh,pH and Cd desorption,whose average values were 400.4 mV,6.11 and 46.78%,respectively.The results indicate that the adsorption and desorption of Cd in soils differed with reduction levels.The adsorption ratio of the adscititious Cd in the strongly reduced soil is less than that in the moderately reduced soil,whereas the desorption ratio of the adscititious Cd decreased with the following order:strongly reduced soil moderately reduced soil aerated soil.The stronger the reduction state,the lower adsorption and higher desorption ratios of Cd in the soil.In addition,Eh,pH,exchangeable Fe2+ and dissolved organic matter(DOM)are major factors to affect Cd adsorption and desorption in soils under the reduced soil condition.