不同pH值下腐殖酸反渗透膜污染中的界面相互作用解析

Analysis of interfacial interactions in reverse osmosis membrane fouling by humic acid Effect of solution pH

应用extended derjaguin-landau-verwey-overbeek(扩展DLVO)理论评价不同pH值下范德华力、静电力、疏水性力3种界面相互作用对腐殖酸反渗透(reverse osmosis,RO)膜污染的贡献,探究pH值影响腐殖酸RO膜污染的主控机制.对3种常规RO膜的理论分析结果表明,静电力对腐殖酸RO膜污染的贡献很小,范德华力使膜污染加剧;疏水性力会减缓膜污染.与前期粘附阶段相比,后期粘聚阶段中范德华力的贡献有所增大,疏水性力在2个污染阶段中均起主导作用.膜污染随pH值的降低而加重,疏水性力作用能的改变是pH值影响系统界面自由能的主控机制.相应pH值下3种RO膜过滤实验数据及其相关性分析结果表明,扩展DLVO理论能定量评价3种界面相互作用的贡献,界面自由能和膜污染之间有很好的相关关系,RO膜纯水接触角的数值不宜作为评价膜污染的指标.

The extended Derjaguin-Landau-Verwey-Overbeek（XDLVO） approach was applied for better understanding of the basic interfacial interactions（i.e.van der Waals interaction,electrostatic interaction and acid-base interaction） involved in reverse osmosis（RO）membrane fouling by humic acid at different pHs.Based on the theoretical calculations with three representative RO membranes,the electrostatic interaction was found to be negeligible in membrane fouling.The van der Waals interaction favored fouling,whereas acid-base interaction could prevent it.The contribution of van der Waals interaction was higher in the cohesion stage than that in the adhesion stage.The acid-base interaction was dominant in both stages.Membrane fouling became less serious as solution pH increased.The surface free energy was affected by solution pH mainly via the alternation of acid-base energy.Correlation analysis of the corresponding fouling data proved that XDLVO approach could successfully describe the characteristics of RO membrane fouling by humic acid and quantitatively evaluate the involved interfacial interactions.The contact angle of RO membrane measured by pure water turned out to be an inappropriate parameter for accurate prediction of membrane fouling.