壳聚糖改性沸石吸附废水中铍(Be)的试验研究

Experimental study of the adsorption of Be to the modified zeolite by chitosan

含铍（Be）废水主要产生于矿产的开采和冶炼等环节。采用碱性条件下负载壳聚糖的方式制取改性沸石,并分析了其吸附水中Be的特性、影响因素、动力学及等温线。FIR、SEM和XRD表征结果表明,壳聚糖负载于沸石表面,使沸石孔径结构和分布得以改善。两种沸石对Be的吸附在3050 min内吸附速率最快,分别在120 min和200 min时达到表观吸附平衡,改性沸石达到平衡所需的时间明显缩短;两种沸石对Be的去除率随初始质量浓度增加而降低,当废水中Be质量浓度不超过排放标准的5倍时（≤0.025 mg/L）,采用1.0 g/L改性沸石处理可以达到排放标准。准一级动力学方程和准二级动力学方程拟合沸石对Be的吸附较为准确,而孔内扩散方程拟合结果较差。Langmuir方程、Freundlich方程均能较好地描述沸石对Be的吸附等温过程。pH值在79时Be的去除率最高。改性沸石吸附性能受pH值影响较大,这可能是因为负载壳聚糖分子中的羟基（—OH）、氨基（—NH2）等活性基团对pH值变化较为敏感。

This paper takes it as its target to present the results of our experimental study of the adsorptive features of Be to the mod- ified zeolite by using ehitosan. There comes the need for the growing concern about the water pollution in our living environment caused by the light-metal ions. As is known, human beings have developed many kinds of functional materials for adsorbing some unnecessary elements in their economic and scientific practice. Sewage containing beryllium （Be） comes mainly from human mining activities and the refining process of the lead-zinc ore, the beryllium and antimony ore. Be in the isolated form or ion form usually can turn to be poisonous or carcinogenic when its ions were accumulated in human bone, liver, kidney and lymph node. To develop a new approach to curing such diseases, it is necessary to develop a new kind of cheap, efficient adsorbent, that is the modified zeolite, which we have prepared in this paper by loading chitosan onto the powdered zeolite. In order to make sure the reliability and effectiveness of our invention, we have analyzed the adsorption characteristic features, their influential factors, the adsorption dynamics and isotherm of the said innovation. We have been trying to sum up the results of FIR, SEM and XRD experiments, which indicate that chitosan can also be loaded on the surface of zeolite. When we were trying to transform the surface morphology from scale-like to porous, we have achieved quick adsorption equilibrium in the first 30 -50 minutes of the adsorptive reactions in the process of 120 minutes-to - 200 minutes＇ experiments, respectively, when the natural and modified zeolite has been adopted. However, the removing rate began to decline when Be was added to its initial concentration. What is more, when the concentration of Be in the sewage was less than 5 times of the effluent standard （ ≤0. 025 mg/L） , it would be possible to modify the zeolite sample in a 1.0 g/L dosage to make it well-matched to the standard one. Thus, the adsorption kinetics proves that the zeolite sample can well be made in accord with the first-and-the-second-order reaction much more precisely than that is gained from the pore-diffusion reaction, which implies that the boundary layer diffusion tends to be the key step to determining the adsorption velocity. Furthermore, Langmuir equation and Freundlich equation can both help to clarify the adsorption isotherm satisfactorily. And, the preferable pH range should be set up between 7 to 9, which is in a position to exert a considerable effect on the adsorption capacity of the natural and modified zeolite, though later testing proves it is more dependent by nature. The situation comes about mainly due to the active groups, such as hydroxide and amidogen in the chitosan molecules, for they are sensitive to the variation of pH.