Effects of Ca ²⁺ on APAM Fouling of Ion Exchange Membranes in Polymer Flooding Wastewater Treatment: Desalination Performance, Characteristics and Mechanisms

Abstract

The effects of calcium ions (Ca²⁺) on anionic polyacrylamide (APAM) fouling of ion exchange membranes (IEMs) in polymer flooding wastewater (PFW) treatment were systematically investigated by associating the desalination performance and physicochemical and electrochemical characteristics with the electrostatic interaction and interfacial free energy. APAM fouling mainly occurred on the anion exchange membranes (AEMs) due to electrostatic attraction, which significantly deteriorated the membrane desalination performance. Under the same experimental conditions, the membrane fouling of APAM with a molecular weight of 6 million Dalton (600APAM) was more serious than that of 0.5 million Dalton (50APAM), and APAM fouling on homogeneous membranes was more serious than that on heterogeneous membranes. Ca²⁺ would connect with the carboxylate ions of APAM by coordination, and as a result, the APAM+Ca fouling layer was denser than the APAM fouling layer. Meanwhile, Ca²⁺ could alleviate APAM fouling because of the increasing zeta potential after CaCl₂ addition, and the electrostatic attraction between APAM molecules and AEM weakened. Both electrostatic interactions and interfacial free energy affected APAM fouling of IEMs, but electrostatic interactions dominated the fouling process. The results contribute to establishing comprehensive understanding of fouling mechanisms and providing guidance for controlling membrane fouling and modification of IEMs.

Keywords: calcium ions, anionic polyacrylamide, ion exchange membranes, polymer flooding wastewater, electrostatic interactions