[Adsorption behavior of cadmium in phaeozem and burozem]

The study on the thermodynamics and kinetics of Cd2+ adsorption in phaeozem and burozem showed that within the test range, Cd2+ adsorption was increased with its increasing initial concentration, and phaeozem had a much higher Cd2+ adsorption capacity than burozem. When the Cd2+ concentration in adsorption equilibrium was 20 mg x kg(-1), the amount of adsorbed Cd2+ was 1 485.2 mg x kg(-1) in phaeozem, but 700.6 mg x kg(-1) in burozem. The adsorption isotherm of Cd2+ in the two soils could significantly conform to Langmuir, Freundlich and Henry equations, while Temkin equation was not applicable to describe the isothermal adsorption process of Cd2+ in phaeozem and burozem. The maximum adsorption of Cd2+ in phaeozem and burozem was 5939.3 and 2 790 mg x kg(-1), respectively, according to Langmuir formulation. The Cd2+ adsorption in test soils was a rapid reaction, with 90% of Cd2+ adsorption in the first 2 min and reached equilibrium in 15-30 min. First-order dynamic equation was the optimal model to describe the kinetics of Cd2+ adsorption, while the other models in point were Elovich and Two-constant equations. The adsorption rate of Cd2+ in test soils was increased with its increasing initial concentration, but decreased with its increasing adsorbed amount. Under low concentrations of Cd2+, the decrease of its adsorption rate with time was more quickly in phaeozem than in burozem.