粉煤灰对水中铅镉的吸附特性和机理研究

Adsorption Characteristic and Mechanism Studies of Lead and Cadmium on Coal-Fired Fly Ash

通过对粉煤灰样品进行表征,探索了其与铅、镉吸附相关的形态和物化特性,并进行了水中铅、镉的静态吸附实验,通过用Langmuir、Freundlich和Tenkin方程对吸附等温线进行建模,分析了铅、镉的吸附平衡性质,且进行了吸附动力学研究以描述其吸附过程,研究了潜在的吸附速率控制步骤和吸附机理。结果表明,粉煤灰样品中未燃炭的含量对铅、镉的吸附有着一定影响,而粉煤灰表面环状硅酸盐中的Al-O/Si-O或Si-O-Si/Si-O-Al官能团对铅、镉的吸附起主要作用。Langmuir等温线方程拟合结果最佳,说明粉煤灰表面结构均匀,对水溶液中铅、镉的吸附既有物理吸附,又有化学吸附,属于单分子层吸附。在25℃条件下,粉煤灰对水中铅、镉的最大吸附量分别为69.9301 mg/g和36.9040 mg/g。相较而言,准二级动力学模型能够更准确地描述吸附过程,说明化学吸附是影响铅、镉在粉煤灰上吸附速率的控制步骤。

Through the characterization of fly ash samples,the speciation and physicochemical properties related to the adsorption of lead and cadmium were explored,and the static adsorption experiments of lead and cadmium in water were carried out.Based on the experimental data,adsorption isotherm was modeled with Langmuir,Freundlich,and Tenkin equations.The adsorption equilibrium properties of lead and cadmium were analyzed,the adsorption kinetics was studied to describe the adsorption process,and the potential adsorption rate control steps and adsorption mechanism were studied.The results showed that the content of unburned carbon in fly ash had a certain influence on the adsorption of lead and cadmium,and the Al-O/Si-O or Si-O-Si/Si-O-Al functional groups in the cyclic silicate on the surface of fly ash played a major role in the adsorption of lead and cadmium.Langmuir isotherm equation presented better fitting result,indicating that fly ash surface was uniform,and the adsorption of lead and cadmium in aqueous solution had both physical and chemical adsorption,which belonged to monolayer adsorption.The maximum adsorption capacity of fly ash for lead and cadmium at 25℃in water was 69.9301 mg/g and 36.9040 mg/g,respectively.The pseudo-second-order kinetic model could describe the adsorption process more accurately,showing that lead and cadmium adsorption on fly ash surface was controlled dominantly by chemical adsorption.