Fundamental Research into the Treatment of the Chromic Plating Rinse by Reverse Osmosis

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Abstract
Fundamental research into the treatment of the chromic plating rinse by reverse osmosis were carried out with Loeb-type skinned membranes. The effect of the pH on the transport of chromic acid was quantitatively investigated. With the increase in pH, chromic acid dissociates to form a divalent ion, CrO42−, and the rejection by the membrane increases. For example, the rejection of 0.01 M chromic acid at pH 3 was 83%, while it was 96% at pH 7.25, both at 40 atm. The permeation behavior of additives such as sodium hexafluorosilicate and chromium (III) sulfate was also examined, mainly in connection with their dissociation in the solution. In the case of the concentration of chromic acid, the rejection remained constant up to about 15000 ppm, while the flux decreased considerably with an increase in the concentration.