Abstract: The sorption properties for U(Ⅵ) and Cu(Ⅱ) ions, alone or mixed, onto raw sunflower straw were systematically evaluated in a series of batch experiments by varying solution pH, adsorbent dosage, temperature, contact time and initial ion concentration. The kinetic data were examined with pseudo-second-order kinetic model, and the equilibrium data obtained were analyzed with Langmuir, Freundlich and Langmuir-Freundlich isotherm equations. It was shown that the positive and negative enthalpy change suggested the endothermic and exothermic nature of U(Ⅵ) and Cu(Ⅱ) ions sorption, respectively. The kinetic data followed pseudo-second-order equation, indicating that the chemical process (adsorption) was rate-limiting step. The equilibrium adsorption data of alone U(Ⅵ) and Cu(Ⅱ) ions could be well described with Langmuir-Freundlich and Langmuir isotherm model, respectively. While for mixed U(Ⅵ) and Cu(Ⅱ) ions Langmuir-Freundlich equation was better for U(Ⅵ) ion at Cu(Ⅱ) concentration more than 60 mg·L^-1, but Langmuir model was best for Cu(Ⅱ) ion at U(Ⅵ) concentration more than 200 mg·L^-1. Obviously, sunflower straw is of an excellent adsorption selectivity toward U(Ⅵ) over Cu(Ⅱ) in terms of distribution coefficient and separation factor, which was likely related to itself properties of metal ion. Furthermore, these results obtained by FT-IR, SEM and EDX revealed that the adsorption mechanism of U(Ⅵ) and Cu(Ⅱ) ions onto sunflower straw is likely to ion exchange and complexation.

Key words: sunflower straw, uranium (Ⅵ), copper (Ⅱ), selectivity, thermodynamics, kinetics, adsorption mechanism

摘要： 以分别含有单一的U（Ⅵ）、Cu（Ⅱ）溶液以及U（Ⅵ）、Cu（Ⅱ）混合溶液为吸附质，系统探讨了pH值、吸附剂量、温度、时间和初始离子浓度对向日葵秸秆吸附效果的影响。采用准二级动力学模型、Langmuir、Freundlich和Langmuir-Freundlich等温吸附模型对实验数据进行拟合，从分配系数和分离因子角度对吸附选择性进行分析，并对吸附机理进行探讨。结果表明：向日葵秸秆对U（Ⅵ）和Cu（Ⅱ）的吸附分别是自发的吸热和放热反应；吸附动力学均符合准二级动力学模型，即化学吸附为控速步骤；单离子体系下U（Ⅵ）和Cu（Ⅱ）的吸附等温线分别符合Langmuir-Freundlich和Langmuir等温吸附模型；复配体系下，当干扰Cu（Ⅱ）浓度≥60 mg·L^-1时，U（Ⅵ） 的吸附等温线可用Langmuir-Freundlich模型描述；而当干扰U（Ⅵ）浓度≥200 mg·L^-1时，Cu（Ⅱ）的吸附等温线可用Langmuir模型描述。当溶液中同时存在U（Ⅵ）和Cu（Ⅱ）两种离子时，离子间存在竞争吸附，且向日葵秸秆对U（Ⅵ）具有更高的选择性，这与金属本身的特性有关。向日葵秸秆吸附前后的SEM、EDX和FT-IR图谱表明，吸附U（Ⅵ）和Cu（Ⅱ）的主要方式为络合和离子交换。

关键词: 向日葵秸秆, U（Ⅵ）, Cu（Ⅱ）, 选择性, 热力学, 动力学, 吸附机理