Monovalent/Divalent Membranes

Anyone know of membranes that have selectivity for monovalent AND divalent ions. We have a client that would like to implement such membrane in an electrolytical system to extract cadmium and nickel from a cadmium/nickel/chromium rich lixiviate. They wish to recover nickel and cadmium as a solution and dispose of chromium as a precipitate. The separation of these metals is achieved through a pH gradient through the electrolytical system, and the requirement of a membrane would be to ensure that no chromium contaminates the product, which in this case would be a rich cadmium/nickel solution.

1 Answer

1. 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.