硅对不同pH水田土壤吸附-解吸镉的影响

Effect of added silicon on adsorption-desorption characteristics of cadmium on paddy soil with different pH

为探讨硅对土壤镉吸附解吸特征的影响,在中和硅酸钠碱性和消除钠离子影响的基础上,进行了不同硅浓度下土壤对镉的等温吸附-解吸试验。结果表明:在试验条件下,Freundlich模型可更好地描述不同硅浓度下2种土壤对镉的吸附-解吸特征;随着加硅量的增加,碱性土壤吸附镉的数量逐渐降低,酸性土壤吸附镉的数量逐渐增加。加硅使碱性土壤方程的k值变小、n值变大,降低了镉的吸附容量却增大了吸附强度;酸性土壤方程的k值变大、n值变小,增加了镉的吸附容量却降低了吸附强度。2种土壤镉的解吸量均随着加硅量的增加而降低,加硅使滞后系数(Δk+Δn)增大,加剧了吸附-解吸过程中的滞后效应。

Adsorption-desorption isotherm experiments were conducted to investigate the effects of silicon on adsorption-desorption characteristics of cadmium on paddy soil with different pH.HNO_3 was used to neutralize the alkalinity of Na_2SiO_3. NaNO_3 was added to keep constant electrolyte concentrations in all the treatments. The effects of silicon addition on soil pH and the influence caused by the attendant ion were eliminated. The results showed that the Freundlich model was optimal to simulate the adsorption-desorption process among the three isothermal absorption-desorption models（Langmuir, Freundlich and Temkin）. Compare with the control treatment, the alkaline soil showed higher adsorption constant（k value increases and n value decreases）, while the acid soil showed lower adsorption constant（k value decreases and n value increases）with increasing silicon addition. Furthermore, the desorption amount and rate of silicon decreased with increasing silicon addition in two soils, and the hysteresis was enhanced. When adding the same amount silicon, the effects of adsorption-desorption of cadmium on the two soils were different： the adsorption and desorption capacity of cadmium in alkaline soil was decreased, and the adsorption capacity of cadmium in acid soil increased and desorption capacity decreased. Both of the two soils demonstrated that the desorption amount was decreased with increasing silicon addition, while the increasing lag coefficients stimulated hysteresis effects of adsorption-desorption.