包气带土壤对Eu(Ⅲ)的吸附

Adsorption of Eu(Ⅲ) on Aerated Zone Soil

为了解废物填埋坑包气带土壤对241 Am等放射性核素的吸附,以Eu代替化学性质相似的Am,研究了吸附时间、液固比、pH、温度、Eu(Ⅲ)浓度、土壤量以及腐殖酸等对包气带土壤吸附Eu(Ⅲ)的影响.实验结果表明,在室温下,当Eu(Ⅲ)的初始质量浓度为100 mg/L,液固比为30:1(V/m),pH为7～8,吸附时间5 h,土壤量为500 mg时,土壤对Eu(Ⅲ)的吸附率在99%以上;Eu(Ⅲ)浓度与吸附量之间的关系符合Langmuir经验公式;腐殖酸的存在,使土壤对Eu(Ⅲ)的吸附率增加,而C2 O2-4和柠檬酸根离子使吸附率显著降低,PO3-4和SO2-4对吸附影响不大.

As an important radioisotope in nuclear industry and other fields, americium-241 is one of the most serious contamination concerns due to its long half-life （T1/2 = 433 a） and its high toxicity. Meanwhile, as a rare earth element, europium has similar chemical character to americium. So, Eu（Ⅲ） is usually used as a substitute for Am（Ⅲ） when the chemical behavior of ^241Am, such as its speciation, translation or migration-sedimentation, should be investigated. In this paper, in order to provide useful reference for adsorption experiment of Am（Ⅲ） on aerated zone soil, the adsorption of Eu（Ⅲ） on the soil, and the effects of various experimental conditions, such as adsorption time, liquid-to-solid ratio, pH, temperature, concentration of Eu（Ⅲ）, mass of soil and humic acid, etc. are investigated. The results show that the aerated zone soil is an efficient adsorbent for Eu（Ⅲ）. More than 99% of the total Eu（Ⅲ） in solutions could he adsorbed by the aerated zone soil at pH = 8 and a liquid-to-solid ratio of 30：1. The adsorption equilibrium is achieved within 5 hour and the optimum pH ranged 5～9. The relationship between concentrations of Eu（Ⅲ） in aqueous solutions and in soil can be described by the Langmuir adsorption equation. Eu（Ⅲ） uptake on the aerated zone soil is a pH-dependent process at pH〈4, but when pH〉4, the adsorption rate of Eu（Ⅲ） on the soil changed minutely. Humic acid could improve the adsorption of Eu（Ⅲ）, while citrate anion and C2O4^2- inhibited the adsorption of Eu（Ⅲ） on the aerated zone soil. However, no significant differences on Eu（Ⅲ） adsorption were observed at 10～40℃.