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Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)

by Larry Zitko, ChromeTech, Inc.
November, 2002

Electrowinning Chromium From Groundwater

Q. This is my case: We have impressed current cathodic protection (ICCP) for the groundwater wells stainless steel screens which has the same principle as plating, the stainless steel screen will act as a cathode, and there are cast iron plates as a anode and all that emmersed in groundwater (the electrolyte). The question is if the groundwater contains Chromium (and other metals), will Cr (or other metals) be able to plate on the anode or cathode, and thus their concentration in groundwater will decrease and not be detectable.

A. My expertise lies in the purposeful electroplating of hard chromium from concentrated baths onto metallic substrates, in order to improve the workpiece through the beneficial properties of the coating. Your situation is pretty far removed, but I'll take a stab at it anyway.

Industrial chromium electroplating is an inefficient process, with cathode current efficiencies in the 10% - 25% range, depending upon chemistry and other parameters. This results in the need for relatively high current densities - typically 1 to 6 amperes/square inch. You did not specify the current density experienced by the stainless steel screen, but if it is very low, significant deposition is not likely to occur. No chromium can be deposited on the cast iron, because it is anodic.

All commercial chrome plating baths require the addition of a chemical catalyst. Sulfate (from sulfuric acid) is widely used as a generic catalyst. Fluoride (from proprietary sources, acids such as hydrofluosilicic acid or even dry acid salts) is another common catalyst. Fluoride is used in conjunction with sulfate in these mixed-catalyst baths. Other commercial, proprietary catalysts have been introduced in the last decade.

Industrial chromium electroplating baths operate at much higher concentrations than your scenario, typically 20 - 50 ozwt/gal. Electrolytic recovery of chromium from dilute solutions (as a pollution prevention or waste minimization strategy) doesn't work very well. Even if a catalyst is present, the low chromium concentration results in unacceptably low plate-out rates on the cathode.

In summary, I would not expect any significant deposition of chromium onto the stainless steel in your situation.




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