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.
Among membrane separation processes [Crespo, 1994; Li, 2008; Field, 2017] osmotic driven techniques are considered as innovative potential industrial methods, although the principle of these procedures has been known for long. Their wide industrial application is, however, hindered by mainly technical difficulties (e.g. the lack of proper membrane materials). In this chapter two promising osmotic membrane processes are presented, where forward osmosis and membrane osmotic distillation were applied for up-concentration of a coconut milk solution and juices obtained from various colourful wild fruits, respectively.
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