磁性生物炭对铅镉离子的吸附动力学

Adsorption kinetics of lead and cadmium ions on magnetic biochar

采用水热合成法制备磁性生物炭,利用XRD、FTIR和BET分析磁性生物炭的结构、官能团种类和比表面积,并研究磁性生物炭对Pb^(2+)、Cd^(2+)的吸附机理。结果表明,磁性生物炭含有丰富的含氧官能团和芳香结构,磁性物质为Fe_(3)O_(4)颗粒。Pb^(2+)、Cd^(2+)在磁性生物炭上的吸附是一个高温自发、吸热且熵增的过程,其吸附过程符合准二级动力学方程,表明化学吸附占据优势,吸附过程是由液膜扩散和颗粒内扩散共同控制。Pb^(2+)在磁性生物炭的吸附机制,主要与含氧官能团(—COOH、—OH、C—O—C)的络合作用和π电子的配位作用有关,还存在氧化还原反应。磁性生物炭吸附Cd^(2+)的机制,主要与—COOH、—OH和π电子的络合作用有关,C—O—C和氧化还原反应不参与磁性生物炭对Cd^(2+)的吸附。

The magnetic biochar was prepared by one step hydrothermal synthesis method and characterised by Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD)and BET technologies.Then it was applied to explore the adsorption mechanism of Pb^(2+) and Cd^(2+).The results showed that magnetic biochar contains oxygen functional groups,aromatic structure,and magnetism is provided by Fe_(3)O_(4).Besides,thermaldynamics parameters indicated that the Pb^(2+) and Cd^(2+) adsorption onto magnetic biochar was a spontaneous at high temperature,endothermic,and entropy-increasing process.The results of kinetics experiments data prove that the adsorption process can be well described by the pseudo-second-order model,which suggests that the whole process is dominated by the chemical adsorption.The adsorption process is cotrolled by both membrane diffusion and internal diffusion.What is more,the mechanisms of Pb^(2+) on magnetic biochar are redox reactions,complexation with oxygen functional groups(—COOH,—OH,C—O—C)and coordination of aromatic-πstructures,respectively.And apart from complexation with C—O—C and redox rections,the dominant mechanisms for Cd^(2+) adsorption are complexation with—COOH,—OH and coordination of aromatic-πstructures.