硅铝比对分子筛吸附氨氮性能的影响

Impact of silica-alumina ratio on ammonium adsorption by molecular sieves

基于X射线荧光光谱法确定的4种ZSM5分子筛硅铝比,分析了不同硅铝比分子筛吸附氨氮性能的差异,结合扫描电镜、X射线衍射分析结果,从分子筛的骨架组成、表面形貌和晶体结构角度,考察了硅铝比对分子筛吸附氨氮性能的影响机制;并探讨了分子筛骨架脱硅对其吸附性能的改善作用,为分子筛应用于污水厂尾水深度脱氮提供技术参考.结果表明,不同硅铝比分子筛的表面形貌、晶体结构与吸附氨氮性能具有显著差异:随着分子筛硅铝比增加,其结晶度下降、晶粒形态逐渐模糊、吸附容量降低;当实际硅铝比由35增大至237时,氨氮平衡吸附量由5.65mg/g降至0.41mg/g,由Langmuir吸附等温式确定的饱和吸附量由6.5963mg/g下降至0.4430mg/g.分子筛吸附过程符合准二级动力学模型,吸附速率受离子交换化学吸附作用机理控制,随着硅铝比升高分子筛的离子交换容量下降,其吸附速率降低.分子筛骨架脱硅能够显著改善其氨氮吸附性能,硅铝比为35的分子筛经碱蚀脱硅处理后,其氨氮平衡吸附量提高81.6%,该方法为改善分子筛吸附性能提供了一种有效的技术途径.

This study examined the difference of ammonium adsorption by molecular sieve with different silica-alumina ratios that were determined using x-rays fluorescence (XRF) method. Based on the results from scanning electron microscopy (SEM) and X-ray diffraction (XRF), It was investigated the adsorption mechanism of molecular sieve under different silica-alumina ratio conditions from the perspective of molecular sieve framework, surface morphology, and crystal structure. Meanwhile, the ammonium adsorption improvement through the desilicification of molecular sieve framework was revealed, and this would provide technical reference for the molecular sieve based deep denitrification of sewage treatment plant effluent. The results indicated that molecular sieves with different silica-alumina ratio had significant variation in surface morphology, crystal structure, and ammonium adsorption performance. It was found that the increased silica-alumina ratio was associated with decreased crystallization, increased obscuring of crystal grain shape, and decreased adsorption capacity. When the silica-alumina ratio rose from 35 to 237, the equilibrium adsorption capacity of ammonium by molecular sieve decreased from 5.65mg/g to 0.41mg/g, and the monolayer adsorption saturation capacity confirmed by Langmuir adsorption isotherm decreased from 6.5963mg/g to 0.4430mg/g. The adsorption process conformed to the pseudo-second-order kinetic model, which was revealed that the adsorption rate was controlled by the mechanism of ion-exchange chemical adsorption. Both the ion-exchange capacity of molecular sieve and the rate of adsorption decreased with the increase in silica-alumina ratio. It was observed that the ability of ammonium absorption was significantly improved by desilicification process of molecular sieve framework, and the equilibrium ammonium adsorption with a silica-alumina ratio of 35increased by 81.6% after a desilicification process. This would provide an effective technological approach for improving the ammonium adsorption by molecular sieve.