Negative Rejection of Group Ib Metal Cyanide Complexes in the Hyperfiltration by Cellulose Acetate Membranes. Donnan Membrane Effect

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Abstract
Anionic cyanide complexes of Group Ib family metal ions, CuICN)− 2, AgICN)− 2 and AuICN)− 2, showed negative rejection in hyperfiltration through cellulose acetate membranes when the feed solution contained such polyvalent anions as succinate, tartrate, aspartate, ethylenediaminetetraacetate, polyacrylate, polyvinylsulfonate, phosphate, and sulfate in a substantial concentration. The dicyanometal complex anions are essentially membrane permeable, while the polyvalent anions are essentially membrane impermeable. Both types of anions combined with the membrane permeable countercations form an ionic ternary system in which the Donnan membrane effect operates to enhance the diffusion of the permeable salt through the membrane, resulting in its enrichment in the permeate solution. By taking advantage of this phenomenon, a selective enrichment of dicyanoargentite in the permeate and its separation from the coexisting transition metals were achieved. Based on this principle, a new hyperfiltration-ultrafiltration technique was proposed for the ion-selective separation of salts.

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