Reverse electrodialysis (RED) is an emerging technology, which can generate clean energy from the mixing of two solutions of different ionic strength. Natural seawater and fresh water are sources of the streams; however, most RED research studies have been conducted using NaCl in synthetic water, which does not reflect the characteristics of natural water sources with multivalent ions. There is a critical need to determine the effect of multivalent ions on overall electrical resistance and performance of ion exchange membranes (IEMs) in RED. In this study, we have investigated the effects of environmentally abundant alkaline earth ions in an NaCl solution on the electrical resistance of IEMs and further on the performance of a bench-scale RED process. We found that the electrical resistance of a cation exchange membrane (CEM) with Mg2+ or Ca2+ ions in an NaCl solution was increased by 145% or 172% respectively compared to that of a CEM with NaCl only. Also, a linear relationship between the electrical resistance of the CEM and the hydration number of various cations was found. As the hydration number of divalent cations decreased (i.e., Mg2+ &gt; Ca2+ &gt; Sr2+ &gt; Ba2+), the electrical resistance of the CEM significantly increased. When a divalent cation (i.e., Mg2+ or Ca2+) was added into an NaCl solution, electrical resistance of the RED stack in a bench-scale RED process increased by 110% or 117% respectively compared to that of the RED stack with NaCl only. The increased electrical resistance of the RED stack adversely affected power generation from the RED process.

Effects of divalent cations on electrical resistance of ion exchange membranes for energy production using reverse electrodialysis

254th National Meeting (2017)

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