硅藻土负载纳米铁对Cd2+的吸附性能与机制研究

为了提高硅藻土(CDt)的吸附能力,采用NaBH_4液相还原二价铁法合成负载纳米铁的硅藻土颗粒(nZVI-CDt),运用扫描电镜(SEM)、傅里叶红外光谱(FTIR)、X射线衍射(XRD)和X射线光电子能谱(XPS)对nZVI-CDt进行表征,采用静态吸附法研究不同吸附条件对CDt和nZVI-CDt吸附Cd~(2+)的影响,并结合等温吸附属性、吸附过程控制步骤以及吸附动力学、热力学属性分析探讨了CDt和nZVI-CDt对Cd~(2+)的吸附机制.结果表明,负载纳米铁后,硅藻土的团聚现象得到改善,分散性更好,表面活性基团向有利于吸附方向发生变化,吸附能力得到显著提升,相对于CDt,nZVI-CDt对Cd~(2+)的吸附量提升了3.9倍;nZVI-CDt对Cd~(2+)的吸附较为迅速,20 min左右就可达到吸附平衡;随着投加量的增加,nZVI-CDt对Cd~(2+)的吸附量呈下降趋势,而初始浓度对Cd~(2+)的吸附影响则正好相反;相对于CDt,溶液初始pH值对nZVI-CDt吸附Cd~(2+)的影响明显减弱;nZVI-CDt对Cd~(2+)的吸附能力受温度影响不大;nZVI-CDt对Cd~(2+)的吸附符合Temkin等温吸附模型和拟二级动力学模型.吸附反应容易进行,且以物理吸附为主,吸附过程控制步骤为发生在微孔内的吸附反应.吸附热力学参数表明CDt和nZVI-CDt对Cd~(2+)的吸附是自发的吸热过程,且系统的无序性增加.

The adsorption behavior and mechanism of cadmium by diatomite-supported nano-iron

In order to improve the adsorption capacity of diatomite, diatomite particles were loaded with nano-zero valent iron (nZVI-CDt), which were synthesized by NaBH₄ liquid phase reduction of Fe (II). The physicochemical structure of the diatomite particles was analyzed using scanning electron microscopy(SEM), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Under various adsorption conditions, the performance of two types of the diatomite on the adsorption of Cd²⁺ was assessed by static adsorption experiments. Results show that when nano-iron was loaded, the surface properties and the adsorption capacity of the diatomites were significantly improved with enhanced dispersion, improved agglomeration and modified surface active groups in favor of adsorption. In comparison, the adsorption capacity of Cd²⁺ by nZVI-CDt increased by 3.9 folds. The adsorption of Cd²⁺ by nZVI-CDt reached equilibrium at about 20 min. With the increasing dosage of adsorbant, the adsorption capacity of nZVI-CDt to Cd²⁺ demonstrated a decreasing trend while the effect of initial concentration of Cd²⁺ shows an opposite manner. Compared to CDt, the effect of initial pH of solution on the adsorption of Cd²⁺ by nZVI-CDt was significantly weakened. The reaction temperature does not show a significant effect. The adsorption of Cd²⁺ by nZVI-CDt well fitted the Temkin thermodynamic adsorption model and pseudo-second-order kinetic model. The adsorption reaction was a rapid process, mainly physical. The control step of each ion adsorption process took place in micro-pores of the diatomite. The results suggest that the adsorption of Cd²⁺ on CDt and nZVI-CDt is a spontaneous and endothermic process.