磷酸根和镉离子在羟基铁改性膨润土表面的协同吸附机制研究

Synergistic adsorption of cadmium and phosphate on hydroxyl-Fe- bentonite complex

聚合羟基金属-粘土矿物复合物广泛存在于自然环境中,对重金属阳离子和含氧酸根阴离子均有很好的吸附能力,因此对这些化合物的环境迁移过程及污染控制具有重要影响.研究采用FeCl3和Na2CO3共同改性膨润土,制备了羟基铁-膨润土复合物(HyFe-Bent).XRD和孔结构分析结果发现,HyFe-Bent的d001由原土的1.52 nm增加到1.81 nm,比表面积由原土的52.2 m2·g-1增大到108.4 m2·g-1.将HyFe-Bent用于同时吸附水中磷酸根(P)和镉离子(Cd),结果表明,在实验条件下P和Cd在HyFe-Bent上表现出明显的协同吸附效应,溶液pH升高可促进Cd的吸附但降低P的吸附.此外研究了P和Cd吸附次序对它们吸附性能的影响:在先吸附P的体系中两种物质的吸附性能与同时吸附体系相当,而在先吸附Cd的体系中吸附性能则明显低于同时吸附体系.由此提出P和Cd协同吸附的原理是多种吸附机制共存:除了配体交换和离子交换作用,它们在HyFe-Bent表面还发生了表面沉淀作用,可能形成了Fe-P-Cd三元络合产物.论文研究结果可为了解重金属和含氧酸根复合体系的环境行为及污染控制提供新信息.

Hydroxyl-metal-clay complexes are ubiquitous in the nature and they have high adsorption capacity towards heavy metal cations and oxy-anions. Therefore, they can significantly influence the environmental transport and pollution control of the above contaminants. In this work, hydroxyl-ferric-Bentonite complex （HyFe-Bent） was synthesized by modifying bentonite with FeCl3 and Na2CO3. XRD characterization results showed that the basal spacing of HyFe-Bent was larger than that of the original bentonite （1.81 nm vs 1.52 nm）. Pore structure analysis results showed that BET surface area of HyFe-Bent was also about twice that of the original bentonite （108.4 m2·g-1 vs 52.2 m2·g-1）. The results of simultaneous adsorption experiments indicated that cadmium cation （Cd） and phosphate （P） could be synergistically adsorbed on HyFe-Bent. On the other hand, the results of sequential adsorption experiments showed that the adsorption capacities of Cd and P could be significantly influenced by their adsorption orders. If P was adsorbed before Cd, both their adsorption capacities were comparable to those obtained from the simultaneous adsorption experiment. However, if Cd was adsorbed before P, their adsorption capacities would decrease evidently. With increasing solution pH from 3 to 6, the adsorption capacity of Cd increased accordingly while that of P decreased. We propose that, apart from the ligand exchange and ion exchange adsorption mechanism, Cd and P may form Fe-P-Cd complex on the surface of HyFe-Bent, which can significantly enhance the adsorption capacity of Cd and P on HyFe-Bent.