改性稻杆吸附U(Ⅵ)的行为和机理研究

通过静态吸附实验,研究了改性稻杆对UO2+2的吸附行为,从吸附热力学和吸附动力学方面对改性稻杆吸附UO2+2的过程进行了分析,并采用红外光谱(FT-IR)、扫描电镜(SEM)、X射线能谱(EDS)、X射线衍射(XRD)等分析手段探讨了改性稻杆吸附UO2+2的机理。结果表明:改性稻杆对UO2+2的吸附过程符合Langmuir等温吸附模型,相关系数达到0.98以上,表现为以单层吸附为主;表面吸附是改性稻杆吸附UO2+2动力学控制的主要步骤,吸附动力学过程符合准二级吸附速率模型,相关系数达0.999 2;热力学研究表明,改性稻杆吸附UO2+2是吸热、自发、不可逆的过程;改性稻杆吸附UO2+2前后的表面形态发生了变化,部分晶体结构发生了改变,吸附过程中改性稻杆细胞壁上的—OH、C O、Si O及P—O等活性基团与UO2+2发生络合反应,形成络合物,故改性稻杆吸附U(Ⅵ)的机理为表面络合吸附。

Study on Adsorption Behavior and Mechanism of U(Ⅵ) by Modified Rice Stem

The adsorption behavior of uranium on modified rice stem was studied through static adsorption experiments. The adsorption process was analyzed by thermodynamics and kinetics, and the adsorption mechanism was analyzed with FT-IR, SEM, EDS and XRD. The results show that the equilibrium adsorption process well fits to Langmuir isotherms model with relation coefficient greater than 0.98, and the monolayer adsorption is predominant form. The kinetic analysis shows that the UO²⁺₂ adsorption rate on modified rice stem is mainly controlled by surface adsorption. The process of adsorption can be well described by pseudo-second-order model with the relation coefficient to 0.999 2. The thermodynamic study indicates that the adsorption process is spontaneous, endothermic and unreversible. The adsorption of uranium on modified rice stem changes the morphology and the crystal characteristics of rice stem. In the adsorption, UO²⁺₂ mainly reacts with —OH, CCDS1]O, SiCDS1]O and P—O, etc. on the cell’s surface of modified rice stem. The adsorption of UO²⁺₂ on modified rice stem should be of chelated surface mechanism.