Application of the _pH-stat technique in donnan dialysis: Effect of anion invasion in the CoSO₄/nafion 117/H₂So₄ system

Cobalt transport during Donnan dialysis in the CoSO4/Nafion 117/H₂SO₄system was measured with a pH-stat technique. (i.e., the pH in the feed compartment was maintained constant). During the transfer process, Co²⁺ ions moved from the cobalt reservoir to the sink compartment, while hydrogen ions moved in the opposite direction. A standardized NaOH solution was used to neutralize the H⁺ ions entering the reservoir compartment, and in the absence of anion invasion, the cobalt flux was determined as [formula omitted] The experimental results indicate that for Donnan dialysis experiments involving high acid concentrations, the invasion of the membrane by the anions associated with the acid can be significant. Since anion transfer is accompanied by the cotransport of protons, it follows therefore that the anion invasion characteristics must be known before the pH-stat technique can be employed successfully. The transport of bisulfate ion (HSO₋₄) through Nafion 117 was measured with the pH-stat technique. An invasion-corrected cobalt flux was obtained by substracting the hydrogen flux due to anion invasion from the cobalt flux determined with the above equation. The invasion-corrected flux was in substantial agreement with the flux obtained via cobalt analysis with atomic absorption spectrophotometry.