4A分子筛对水中铅离子的吸附及其机理分析

Adsorption of Lead Ions from Aqueous Solution onto 4A Molecular Sieve and Mechanism Analysis

以4A分子筛、阳离子交换树脂和活性炭作为吸附材料对Pb2+吸附性能进行对比,并通过吸附等温线和动力学方程拟合得到,4A分子筛对Pb2+的吸附速率常数为0.014 9 g/(mg·s),吸附容量为595.2 mg/g,高于阳离子交换树脂的0.000 5 g/(mg·s)和203.3 mg/g,以及活性炭的0.001 9 g/(mg·s)和177.3 mg/g,且吸附过程主要受液膜扩散控制。对比分析4A分子筛对不同价态金属离子Ag+、Pb2+和Cr3+的吸附,结果表明:分子筛对金属离子的吸附与价态数成反比,价态越高,吸附反应速率越低;且吸附过程主要为同电性、等电量的离子交换吸附。分子筛吸附Pb2+前后元素组分、晶体结构和表观形貌的变化表明:分子筛对Pb2+的吸附是分子筛中的Na+与溶液中游离的Pb2+发生离子交换的过程,经吸附后的4A分子筛的晶体结构和表面形貌保持不变。Zeta电位分析表明,4A分子筛与铅离子的作用方式中存在着静电吸引的物理吸附。

Performance of Pb2 ＋ adsorption from aqueous solution onto molecular sieves was experimentally studied in comparison with those of other adsorption materials such as cation exchange resins and activated carbon. Through fitting the adsorption isotherm and kinetics equation,it was found that Pb2＋ adsorption rate constant onto 4A molecular sieve was0.014 9 g/（mg·s） and the adsorption capacity was 595.2 mg/g,higher than those of cation exchange resins and active carbon;and the adsorption process was mainly controlled by the liquid film diffusion. By comparing the adsorption behaviors of different valence metal ions such as Ag＋,Pb2＋ and Cr3＋,the study suggested that the adsorption rate was inversely proportional to the number of valence, the higher the valence,the lower was adsorption rate;meanwhile,adsorption process were characterized with the ion-exchange adsorption of the same electrical properties and equal quantity. Furthermore,the fact that variations in terms of element component,crystal structure and apparent morphology of molecular sieves before and after Pb2＋adsorption onto molecular sieves indicated that Pb2＋adsorption process was caused by replacing Na＋ions within the molecular sieve with free Pb2＋in the solution;and the crystal structure and morphology of 4A molecular were not changed actually after Pb2 ＋being adsorbed. Besides,analysis using Zeta potential measurement showed that there existed physical adsorption with electrostatic attraction between 4A molecular sieve and lead ions.