Membrane fouling behavior and cleaning control of a dual-charged nanofiltration membrane in treating acid mine drainage after neutralization

Abstract

The study evaluated the membrane fouling behavior of a dual-charged nanofiltration (NF) membrane in treating acid mine drainage (AMD) after neutralization. After 10hours of fouling, the membrane demonstrated an 89.52% recovery rate and exhibited excellent retention ability for divalent ions (91.21% Mg2+, 89.24% Ca2+, 91.51% Mn2+, 93.72% SO42-), as well as outstanding anti-pollution performance. Membrane fouling characterization revealed that the primary cause of membrane fouling was inorganic salt fouling from CaSO4 and MgSO4. In the initial stage of NF separation, when the inorganic salt fouling was close to the membrane surface, the adhesion-free energy between the membrane and the inorganic salt fouling was dominant, causing the inorganic salt fouling to be deposited on the membrane surface. As time progressed, the deposited inorganic salt fouling gradually covered the membrane surface, with agglomeration-free energy between the inorganic salt fouling dominating subsequent stages of membrane fouling. The fitting of the membrane plugging model revealed that, in addition to the deposition of inorganic salt fouling on the membrane surface, some inorganic salt fouling would also penetrate the membrane pores and obstruct them, leading to a rapid decline in membrane flux and subsequently reducing the membrane separation performance. Following cleaning with deionized (DI) water, citric acid (CA), NaOH, and EDTA, it was observed that the CA cleaning agent achieved the highest membrane flux recovery rate at 91.84%. The EDTA cleaning agent demonstrated superior retention effects on bivalent ions (94.21% Mg2+, 93.21% Ca2+, 96.74% Mn2+, 97.45% SO42-). This work provides a reference direction and theoretical guidance for the behavior and control strategy of membrane fouling in neutralized AMD treated by the dual-charged NF membrane.