To analyze the desorption characteristics of aluminum in planosol soil with aluminum pollution

balanced oscillating method was applied to study the aluminum desorption behavior and the influence of different factors in planosol soil. The results showed that the aluminum desorption in planosol soil reached equilibrium after 720 min. At 25 ℃

the content of soil organic matter was 42.2 g/kg

and the desorption capacity of aluminum in planosol soil was only about 1.5% of the adsorption capacity. The Langmuir equation fit well on the desorption isotherm of aluminum in planosol soil (r=0.985 9**) and showed that the surface uniform monolayer dominated desorption. The thermodynamic parameters ΔG＜0

ΔH＞0

ΔS＞0 indicated that the aluminum desorption was a spontaneous

endothermic

and entropy increase process. The content of soil organic material decreased from 42.2 g/kg to 27.8 g/kg

the maximum desorption of aluminum in planosol soil increased from 25.87 mg/kg to 66.11 mg/kg

and the phenomenon of desorption hysteresis was enhanced. When the pH dropped to 3

the aluminum desorption capacity rapidly rose to 226.4 mg/kg

which was 8 times more than that at pH 5～7. With the increased concentration of NaCl and Na2SO4 in the desorption solution

the desorption capacity of aluminum also increased. In a word

the desorption capacity of aluminum that absorbed into planosol soil was relatively weak

but the desorption capacity of aluminum greatly increased

and the risk of pollution sharply increased with the decreased pH and the content of organic matter

and the increased content of inorganic salt.