腐植酸对Cd在西部黄土上吸附特性影响的研究

Adsorption Characteristic of Cd on Loess Soil Affected by Humic Acid

选用西北地区粘土为供试土样,采用振荡离心法研究了腐植酸对Cd在粘土上吸附特性以及相关因素的影响。结果表明,无论是否加入腐植酸,Cd的吸附都能够较好地符合Freundlich方程。在25℃时,加入10 mL55 mg.L-1的腐植酸使土样对Cd的饱和吸附量由29.22 mmol.kg-1增加到31.39 mmol.kg-1,并且Cd在供试土样上的吸附量随温度升高而降低,表明吸附为放热过程。加入与不加腐植酸相比,吸附标准自由能改变量分别为ΔG2θ=-0.949 7 kJ.mol-1和ΔG1θ=-0.888 5 kJ.mol-1。不加腐植酸时,描述Cd在供试土样上的吸附动力学最优方程为Elovich方程,其次为双常数方程;加入腐植酸溶液后,其吸附动力学最优方程改变为双常数方程,且Cd的吸附平衡时间缩短。随着加入腐植酸量的增加,土壤样品对Cd的吸附量明显增加;随pH值的增加,加入腐植酸降低了土壤对Cd的吸附增加量。

Vibration-centrifuge method was used to study adsorption characteristic of Cd on loess soil affected by humic acid. The results showed that the adsorption of Cd on loess soils fitted well with Freundlich isothermal equation no matter with or without humic acid, and the adsorption quantity of Cd increased from 29.22 mmol·kg^-1 to 31.39 mmol·kg^-1 by adding 10 mL 55 mg· L^-1 humic acid solution at 25℃.The adsorption capacity of Cd reduced with increasing of environmental temperature, indicating that adsorption of Cd was an exeergic process, meanwhile, the adsorption standard free energy changed from △G1^θ=-0.888 5 k J· mol^-1 to △G2^θ=-0.949 7 k J· mol^-1 at presence of humic acid. The adsorption kinetics of Cd best fitted with Evolich kinetics equation, and then was double constant equation, but at presence of humie acid, it changed to double constant equation. The adsorption speed of Cd was faster than that without humic acid. The adsorption capability of Cd increased with humic acid concentration and the solution pH increasing. The adsorption quantity of Cd was higher at low pH.