Hi Kevin:Seawater and ...

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Hi Kevin: Seawater and brackish water reverse osmosis membranes available on the market can reject equally well (over 99.9 %) of both monovalent and divalent ions - such as cadmium, nickel and chromium. Nanofiltration membranes reject divalent ions very well (over 99 %) but they have limited rejection of monovalent ions (10 to 30 %). Unfortunately, there are no commercially available RO or nanofiltration membranes which have ability to selectively remove only one or two mono- or divalent ions - they remove all of them at about the same rate. Ion exchange is a better technology for selective removal of specific ions - but it is much more costly.