聚丙烯酸改性凹土对Pb2+、Ni2+和Cr3+的选择性吸附

摘要

通过凹土的表面功能化开发高性能低成本的吸附材料，采用溶液聚合法在其表面接枝聚丙烯酸，制备出聚丙烯酸/凹土吸附材料（PAA/ATP），系统考察了PAA/ATP对Pb2+、Ni2+和Cr3+三元混合体系的吸附性能。结果表明：PAA/ATP复合吸附材料的有机物接枝率为14.1%，其结构中出现聚丙烯酸的特征官能团；PAA/ATP吸附Pb2+的动力学符合拟二级动力学，即化学吸附是速率控制步骤，说明PAA/ATP对Pb2+的吸附是一个有化学作用的过程，吸附过程与 Pb2+和吸附剂 PAA/ATP 表面官能团之间的电子转移或电子共用有关；PAA/ATP 对 Pb2+的吸附符合Langmuir吸附等温模型；PAA/ATP对Pb2+、Ni2+和Cr3+的竞争吸附能力依次为Pb2+＞Cr3+＞Ni2+，即对Pb2+具有较好的选择性吸附。%Attapulgite (ATP) is a hydrous layer-ribbon magnesium aluminum silicate mineral with a unique three-dimensional structure. Due to its natural abundance, extremely good mechanical/thermal stability, its one-dimensional nanoscale, and a large quantity of silanol groups on the surface, attapulgite is a very good candidate for low-cost materials as adsorbents. To increase adsorption capacity and selectivity, attapulgite must be treated with organo-functional groups to produce specific sites on the surface. Polyacrylic acid/attapulgite (PAA/ATP) was prepared by grafting PAA onto γ-methacryloxypropyl trimethoxy silane (MPS)-modified attapulgite surface via solution polymerization. PAA/ATP was characterized by thermogravimetry (TG) and X-ray photoelectron spectroscopy (XPS). The selective adsorption of ternary mixed heavy metal ions (Pb2+, Ni2+ and Cr3+) by polyacrylic acid/attapulgite composite adsorbents was evaluated in batch experiments by varying contact time and initial ion concentration. The kinetic data was fitted with the pseudo-second-order kinetic model, and the equilibrium data obtained was analyzed with the Langmuir and Freundlich isotherm equations. The kinetic data followed pseudo-second-order equation, indicating the chemical adsorption was the rate-limiting step process. The equilibrium adsorption data of Pb2+ could be described well with the Langmuir isotherm model. Obviously, PAA/ATP showed excellent adsorption selectivity for Pb2+compared with Ni2+and Cr3+in terms of distribution coefficient and separation factor, which was also confirmed by XPS.