磁性污泥基生物炭对Pb2+的吸附性能

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Pb²⁺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Pb²⁺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Pb²⁺去除率基本无影响。MSBC-2对Pb²⁺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k₂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Pb²⁺的吸附机理主要包括表面络合、离子交换和物理吸附。

Adsorption performance of magnetic sludge-derived biochar towards Pb2+

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 Pb2+ adsorption performance were investigated, together with adsorption kinetics, isotherms, and thermodynamics. The results revealed that Pb2+ 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 Pb2+ 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 k2 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 Pb2+ adsorption mechanism onto MSBC-2 included surface complexation, ion-exchange reactions and physical absorption.