磁性污泥基生物炭对Pb^(2+)的吸附性能

Adsorption performance of magnetic sludge-derived biochar towards Pb

为克服湿法制备磁性生物炭颗粒时团聚严重、固液分离困难、热解前需消耗大量能源脱水干化的问题,本研究以市政污泥为原料,通过无溶剂法热解制备了磁性污泥基生物炭(MSBC-2),并利用SEM、FTIR、XPS、VMS和Raman等方法对产物的表面结构与特征进行了表征。基于序批实验,分析了pH、温度、背景离子强度、生物炭投加量对该吸附材料的Pb^(2+)吸附性能的影响,并进行了吸附动力学、吸附等温线及吸附热力学研究。结果表明:MSBC-2的Pb^(2+)去除率随pH及温度的升高而升高,pH>4后去除率基本不变,离子强度对Pb^(2+)去除率基本无影响。MSBC-2对Pb^(2+)的吸附行为符合准二级动力学模型及Langmuir模型,表明吸附过程的限速步骤为化学反应,吸附为单分子层吸附;MSBC-2的反应速率常数k_(2)是未改性生物炭的4.1倍,25℃时最大理论吸附容量为113.36 mg·g^(−1),高于大多数湿法制备的磁性生物炭;该吸附过程非自发、吸热且熵增过程;MSBC-2对Pb^(2+)的吸附机理主要包括表面络合、离子交换和物理吸附。

In order to overcome severe agglomeration,solid-liquid separation problems for magnetic biochar particles in wet preparation process,and high energy consumption for dewatering and drying before pyrolysis,a type of magnetic sludge-derived biochar(MSBC-2)was prepared by solvent-free pyrolysis method with municipal sludge as the raw material.The SEM,FTIR,XPS,VMS,and Raman techniques were applied to characterize MSBC-2.Based on the batch experiment,the effects of pH,temperature,background ionic strength,and adsorbent dosage on the Pb^(2+) adsorption performance were investigated,together with adsorption kinetics,isotherms,and thermodynamics.The results revealed that Pb^(2+) removal efficiency by MSBC-2 increased as pH and temperature rose,but remained stable when pH was above 4.The removal efficiency was almost unaffected by background ionic strength.The Pb^(2+) adsorption process onto MSBC-2 followed the pseudo-second-order kinetic model and Langmuir model,implying that chemisorption was the rate-limiting step and the adsorption process was monolayer adsorption.The reaction rate constant k_(2) of MSBC-2 was 3.1 times greater than that of the sludge-derived biochar without modification.The maximum theorical adsorption capacity of MSBC-2 was 113.36 mg·g^(−1) at 25℃.The adsorption was non-spontaneous,endothermic,and entropy-increasing process.The Pb^(2+) adsorption mechanism onto MSBC-2 included surface complexation,ion-exchange reactions and physical absorption.