Electrolytic Stripping – a “Greener” Alternative to Immersion Stripping

With the environmental pressures being placed on metal finishers today, finding “greener” technologies that are more environmentally friendly and cost effective is a big focus.  The solution chemistry (or pH) can be of alkaline (> 7.0), acidic (< 7.0) or neutral (= 7.0) in nature.  Although chemical immersion strippers are most widely used today, electrolytic stripping is gaining more popularity.

Chemical immersion strippers have a limited bath life. Acidic strippers, such as mineral acids (i.e.- nitric acid, etc.) are tenacious on racks, causing dehydration of the plastisol coating and increasing rack maintenance cost) and are aggressive on ventilation systems however provide adequate stripping rates and acceptable solubility of metals being stripped.

There are still a number of finishers using cyanide base technology today as these types of strippers dissolve most plated metals without attacking steel substrates and strip at an acceptable speed. Although these solutions are favorable in performance, many platers today do not want cyanide containing solutions in their shop.

Alkaline non-cyanide alternatives are available for those looking for cyanide free technology.  Common applications include stripping of copper used for heat treat stop-off or in stripping electrolytic nickel or electroless nickel off steel.  They also are generally operated at temperatures above 140 degrees F and require sufficient ventilation.  An amine or ammonia base stripper is used to provide complexing ability of the stripped metals but poses major difficulty in waste disposal of the spent solution (and waste stream) and chelates (ties up) metals thus making it difficult to precipitate out in the flocculation process in waste treatment process.

Although the set-up cost is higher (due to equipment requirements needed such as rectification, etc.), electrolytic stripping is much safer for the worker as they are neutral (or slightly acidic) in pH.  Another benefit is less degradation of the plastisol coating on racks occur, significantly reducing rack maintenance cost commonly seen in acidic strippers like nitric acid.  An application commonly used is in stripping electrolytic nickel off stainless steel rack tips. The overall quality of deposit is enhanced as a result of the elimination of the robbing effect of the current due to the excessive nickel buildup on the tips. Use in stripping electrolytic nickel deposits on steel is also a common application.

These baths can be desludged which extends their bath life.  An indexing type paper filter is commonly used. They are favorable for waste disposal systems as they contain less complexing agents, thus the metal(s) are more readily precipitated after pH adjustment and offer a “greener” technology in today’s finishing environment.