水铝英石对Cs的吸附及固化性能研究

Adsorption and Solidification Property of Allophane for Cs

^(137)Cs在乏燃料中具有高产额、强放射性、高释热等特点,为将^(137)Cs进行稳定固化保证其长期处置安全,本文研究了水铝英石对Cs的吸附性能、固封性能和固封机制。通过调控溶液的初始浓度和pH值,研究了水铝英石对Cs的吸附性能。结果显示,在pH=5条件下,Cs的吸附率为90%,饱和吸附容量达11.1 mg/g。Cs在水铝英石上的吸附为单层吸附与多层吸附的共同作用。通过冷压-烧结工艺制备了铯榴石陶瓷固化体,研究了烧结温度和固化配方对烧结产物性能的影响。实验表明,烧结温度为1200℃时,可生成铯榴石晶相,减容率超过55%,Cs固定率接近100%,说明水铝英石能稳定固封Cs。固化体的晶相结构与Cs的含量有关,当Cs质量含量为1%时,K原子在高温下能与Cs发生类质同象,形成Cs_(x)K_(1-x)AlSi_(2)O_(6)混晶结构,达到10%时主要为铯榴石晶相。密度泛函(DFT)计算揭示,Cs以离子键和共价键形式与铯榴石晶体中的其他原子结合。

^(137)Cs,with high radioactivity and heat generation,is one of the main fission products in spent fuel.The stable solidification of^(137)Cs is beneficial to ensure the safety of its long-term disposal.The adsorption behavior,solidification properties and mechanism for Cs by allophane were studied in this paper.By varying the initial concentration and pH of the solution,the adsorption percentage of Cs is obtained more than 90%and the maximum adsorption capacity reaches 11.1 mg/g under the condition of pH=5.The adsorption mechanism was governed by the joint action of single-layer adsorption and multi-layer adsorption.The solidified bodies were prepared by pressing and sintering.The effect of sintering temperature and mixing ratios on the properties of the sintered product was studied.Experiments and density functional theory(DFT)calculations show that the crystalline phase of solidified product is formed at 1200℃,the volume reduction ratio is over 55%,and the Cs immobilization ratio is nearly 100%.When the content of Cs in the solidified bodies is 1%,the K atom could substitute Cs atom through isomorphism and subsequent forming Cs_(x)K_(1-x)AlSi_(2)O_(6)crystal structure at high temperature.When the content of Cs reaches 10%,the main crystal phase is determined as pollucite.Cs atom is immobilized by forming ionic bonds and covalent bonds in the pollucite crystal structure with the bond energy of 5.85 eV.