枯草芽孢杆菌与水体中U(Ⅵ)的作用机制

通过静态吸附-解吸实验,研究了枯草芽孢杆菌对U(Ⅵ)的吸附热力学和动力学,U(Ⅵ)的解吸和菌体内P的释放过程,利用扫描电镜、能谱(SEM-EDS)和红外光谱(FTIR)分析了作用机理。结果表明:当p H=5时,在1 L50 mg·L-1的铀溶液中,投加枯草芽孢杆菌1.384 mg(干重,DW),2 h后,铀的去除率和吸附量分别为85.34%和308.31 mg·g-1(DW)。随着作用时间从2 h延长至48 h,铀的解吸率从52.13%下降至36.25%,菌体内释放到溶液中的P浓度从0.12 mg·L-1增加到0.40 mg·L-1。枯草芽孢杆菌对水体中U(Ⅵ)的吸附行为可以用Langmuir吸附等温模型和准二级动力学方程较好地描述。作用过程是放热,可自发进行。SEM-EDS表明枯草芽孢杆菌与水体中U(Ⅵ)作用后,菌体内部断裂呈短节状,铀沉积在细胞表面及周围,无明显晶体产物生成,FTIR图谱出现UO22+特征吸收峰,氨基、磷酸基团参与枯草芽孢杆菌与水体中U(Ⅵ)的作用。

Mechanisms of action between Bacillus subtilis and uranium(Ⅵ) in water

The adsorption thermodynamics and kinetics of uranium adsorption by Bacillus subtilis, desorption of U(Ⅵ) in saturated ethylene diamine tetraacetic acid (EDTA), and phosphorus release into water were studied by static adsorption and desorption experiments. The mechanisms of action were discussed using data from scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) measurements. Optimized uranium removal occurred at pH 5 of 50 mg·L^-1 uranium solution and uranium removal efficiency and adsorption quantity reached 85.34% and 308.31 mg·g^-1(dry weight)after 2 h, respectively. As the duration from 2 h increased to 48 h, desorption rate of uranium reduced from 52.13% to 36.25%, and concentration of P released from Bacillus subtilis increased from 0.12 mg·L^-1 to 0.40 mg·L^-1. Langmuir isotherm and pseudo-second equations could describe well the uranium adsorption behavior by Bacillus subtilis. The process was exothermic and spontaneous. SEM and EDS showed that the cell of Bacillus subtilis was sub-internal fracture, and uranium deposited on the surface and surrounding of Bacillus subtilis without obvious U-P crystal products. FTIR revealed that the surface of Bacillus subtilis possessed many active groups, such as hydroxyl, amide, and phosphate groups, and the amide and phosphate groups were involved in adsorption of U(Ⅵ) by Bacillus subtilis. FTIR spectra showed the characteristic absorption peak of UO₂²⁺.