Nanofiltration of Simulated Acid Mine Drainage: Effect of pH and Membrane Charge

Abstract

Acid mine drainage (AMD) is a severe form of environmental pollution that has the potential to contaminate surface and ground waters by introducing heavy metals and lowering the pH. The feasibility of using nanofiltration (NF) as a potentially attractive and cost-effective remediation method to treat acid mine drainage was investigated in this study. The performance of an acid-stable NF membrane focusing on the effects of the water pH and membrane charge on ion rejection was systematically studied. A single salt solution experiment showed that Mg, Cu, and Mn containing species were highly rejected at above 97%. Below the membrane iso-electric point (IEP), Mn showed an increased rejection of 99%, while Mg and Mn rejections were relatively constant within the investigated pH range of pH 2 to 7. Rejection of monovalent Cl− decreased with increasing concentration of an accompanying divalent SO42−, showing that Donnan related effects are more prominent at higher ionic concentrations. The sulfate rejection decreased drastically below pH 3 due to the formation of HSO4−, which permeated through the membrane, which can be utilized as a way of separation of the metals from the accompanying sulfur-containing compounds. For mixed salt solutions, rejection of silicate dropped from 52% to 38% when magnesium sulfate was added, owing to shielding of the membrane surface charge by Mg2+ ions. The NF process performance with a simulated AMD solution was found to be similar to that with model salt solution experiments, both in terms of ion rejection values and general pH-dependent rejection trends. The results obtained can be used as a fast preliminary tool for evaluating the feasibility of using NF for treating AMD with a given ionic composition and pH.

Mechanical properties and electrical surface charges of microfibrillated cellulose/imidazole-modified polyketone composite membranes

“…These groups induced a charge compensation effect to the MFC fibres. Isoelectric points close to 4.5 have been reported for polymeric membranes based on polyamide [51], polyacrylonitrile [52] or polyamidoamine [53], similarly to our C-IMP composite membrane.…”

Treatment of Electroplating Wastewater Using NF pH-Stable Membranes: Characterization and Application

“…By efficient cell design and appropriate hydrodynamic conditions (discussed in a previous work [29]), concentration polarization effects are deemed negligible. Therefore, the calculated observed rejection is expected to be very similar to the real rejection value.…”

“…A previous in-house study devoted to the effect of pH and membrane charge on the nanofiltration of acid mine drainage showed promising results in terms of simultaneous high heavy metals rejection and low rejection of sulfates, which can be utilized as a way of separating the metals from the accompanying sulfur-containing compounds [29]. The transport of inorganic species coupled to changes in their speciation has been studied by López et al [30], who also report a strong decrease in the rejection of total sulphate (SO 4 2− /HSO 4 − ) as the fraction of single-charged hydrogen sulphate (HSO 4 − ) in the feed increases.…”

Intrinsic pKa of Nanofiltration Membrane Surfaces to Assess Fouling and Cleaning Behaviors Induced by Foulant–Membrane Electrostatic Interactions

“…Membrane surface charge is one of the main factors influencing permeate water flux and salt rejection − and has been rigorously investigated over the past few decades. − The electrostatic repulsive forces between charged foulants and membrane surfaces play an important role in alleviating the permeate water flux decline in polymeric membranes. − In addition, ion rejection by the membrane is significantly influenced by the surface charge on the membrane according to the Donnan theory. − …”

“…When a membrane contacts an aqueous solution, the membrane surface charge can be altered via the ionization of functional groups attached to the membrane surface (e.g., −COOH, −NH 2 , or −SO 3 H). , The ζ-potential of the membrane surface, determined using electrophoresis and the streaming potential, has been utilized as a surrogate indicator to represent the surface charge of polymeric membranes because it theoretically indicates the electrokinetic potential at the slipping plane in the electrical double layer . The ζ-potential is not adequate for accurately evaluating the membrane performance compared to the surface charge determined using potentiometric titration .…”