XDLVO理论解析钙离子对腐殖酸反渗透膜污染的影响机制

Reverse Osmosis Membrane Fouling by Humic Acid Using XDLVO Approach:Effect of Calcium Ions

以XDLVO(extended Derjaguin-Landau-Verwey-Overbeek)理论定量解析腐殖酸反渗透(reverse osmosis,RO)膜污染过程中的界面相互作用,分析3种界面相互作用力在膜污染过程中的贡献,重点探究不同溶液pH条件下Ca2+对腐殖酸RO膜污染的影响.结果表明,无论Ca2+是否存在,对膜污染起促进作用的范德华力在pH 3时为主导作用力,而减缓膜污染的极性作用力在pH 7及pH 10时成为主控因素.静电力在所有测试条件下作用微弱,因此对膜污染贡献很小.Ca2+主要通过改变极性作用力影响腐殖酸RO膜污染行为,且其影响随溶液pH值的降低而凸显,多数情况下Ca2+会促进腐殖酸RO膜污染.界面自由能与膜污染程度相关性分析表明,XDLVO理论可以合理预测不同溶液条件下腐殖酸RO膜污染行为.

Interfacial interactions involved in reverse osmosis(RO) membrane fouling by humic acid were quantitatively evaluated using the XDLVO(extended Derjaguin-Landau-Verwey-Overbeek) approach.The role of each individual interfacial interaction during membrane fouling was elucidated with special emphasis devoted into the influence of Ca2+ under different solution pHs.The results showed that,regardless of the presence of Ca2+,van der Waals interaction favoring fouling contributed the most to the interfacial interactions at pH 3,whereas the polar interaction inhibiting fouling played a dominant role at pH 7 and pH 10.Electrostatic double layer interaction appeared to be the weakest in all cases,thus contributing the least to membrane fouling.It was the changing of polar interaction that gave rise to the influence of Ca2+ on membrane fouling,which turned out to be more significant at lower pH.Ca2+would accelerate humic acid RO membrane fouling at most cases.Correlation analysis between interfacial free energy and fouling extent revealed that XDLVO approach could reasonably predict humic acid RO membrane fouling behaviors under different solution conditions.