Au(Ⅲ)离子在黑曲霉菌上的吸附热力学和动力学特性

以黑曲霉菌作为生物吸附剂,研究其对Au(Ⅲ)离子的吸附特性,考察了pH值、吸附时间、温度和初始Au(Ⅲ)离子浓度等因素对吸附过程的影响。结果表明,Au(Ⅲ)离子在黑曲霉菌上的吸附过程对溶液pH值具有一定的依赖性,最佳pH值为2.0～3.0。升温能明显加快吸附进程,20℃下吸附过程分为2个阶段进行,分别对应于Au(Ⅲ)离子还原前和还原后的吸附,24 h后吸附趋于平衡,而30、40、60℃下吸附过程均无明显分段现象,并分别于12、6、1 h后趋于吸附平衡。Au(Ⅲ)离子初始浓度<233.32 mg·L^-1时,吸附量几乎不随温度的变化而变化,初始浓度>367.94 mg·L^-1时,升温明显促进了吸附的进行。Au(Ⅲ)离子在黑曲霉菌上的吸附等温线可用Langmuir方程很好地模拟,20、30、40、50℃时其饱和吸附量分别为185.19、202.02、235.85、277.78 mg·g^-1。热力学参数Gibbs自由能变(ΔG⁰)、吸附焓变(ΔH⁰)和吸附熵变(ΔS⁰)的计算结果表明,Au(Ⅲ)离子在黑曲霉菌上的吸附过程是一个自发的吸热和熵增过程。吸附动力学可用准二级速率方程描述,吸附活化能为55.71 kJ·mol^-1。傅里叶变换红外光谱分析的结果进一步揭示了菌体表面的酰氨基、羧基和羟基是参与吸附的主要功能基团。

Thermodynamic and kinetic characteristics of Au(Ⅲ) biosorption onto Aspergillus niger

The adsorption behavior of Au(Ⅲ) onto Aspergillus niger biomass was investigated in aqueous solutions.The effects of pH value, contact time, temperature and initial Au(Ⅲ) concentration on the adsorption were studied.The results indicated that Au(Ⅲ) adsorption onto Aspergillus niger was slightly pH-dependent and the pH value of 2.0—3.0 was favorable.The process was obviously accelerated with the increase of temperature in the range of 20—60℃.Au(Ⅲ) adsorption involved two stages at 20℃, corresponding to the periods before and after Au(Ⅲ) reduction and achieved equilibrium at a contact time of 24 h, while the adsorption proceeded in one stage at 30, 40 and 60℃ and achieved equilibrium at 12, 6, and 1 h, respectively.The adsorption capacity was hardly affected by temperature at lower initial Au(Ⅲ) concentrations(<233.32 mg·L^-1), while a significant increase was observed with the increase of temperature at higher Au(Ⅲ) concentrations(>367.94 mg·L^-1).Au(Ⅲ) adsorption fits the Langmuir model well, and the maximum Au(Ⅲ) uptake capacity is 185.19, 202.02, 235.85 and 277.78 mg·g^-1 at 20, 30, 40 and 50℃, respectively.The calculated thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes(ΔG⁰,ΔH⁰,ΔS⁰) reveal that this biosorption is spontaneous and endothermic and entropy increases.The adsorption process conforms to the pseudo-second-order kinetics, with the activation energy of 55.71 kJ·mol^-1.Fourier transform infrared spectra illustrate that the functional groups such as amido, carboxyl and hydroxyl may be responsible for the interaction between Au(Ⅲ) and Aspergillus niger biomass.