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Tolerable conc. of copper for cyanide zinc baths

My cyanide zinc plating bath is contaminated with copper.I know how to remove this impurity but I don't know the tolerable concentration of copper for cyanide zinc baths? anybody know?

Ali Showkati
Faravaresh Felez - Tehran-Iran

Hanson-Van Winkle-Munning Myron B. Diggin, states that as little as 0.075 grams copper/liter has an effect on the deposit. 0.30 g/l will show darkness in the deposit after 1/2% nitric dip.

Copper is removed with low current cathode dummy, density (up to 2 amperes/square foot) until the copper concentration has been reduced to less than 0.04 oz./gal (0.3 g Cu/liter), then use zinc dust ⇦ on eBay or Amazon [affil link] , 1-5 lbs./ 100 gallons of solution volume, filter after 20 - 60 minutes.

Tom Pullizzi
Falls Township, Pennsylvania

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