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topic 32955

Etching of ABS for Electroplating with chromic-sulphuric acid: disposal, alternatives, operational issues

A discussion started in 2005 but continuing through 2018


Q. Please suggest an ABS etching solution discard procedure.

bawale sanjay
Bawale Sanjay D.
- Aurangabad, Maharashtra, India


Q. In our ABS plating shop, etching solution contains high chromic acid so please suggest a discard procedure.

vishwas nangare
Vishwas Nangare
motorcycle accessories mfgr.
- Aurangabad, Maharashtra, India

"Plating Waste Treatment"
by Kenneth F. Cherry

from Abe Books
info on Amazon

A. Hi. Etching solution is indeed a very strong mixture of chromic and sulphuric acid. The chrome must be reduced from Cr+6 to Cr+3 by the addition of sodium metabisulfite or sulfur dioxide at a somewhat acidic pH. Too low a pH and you'll release too much sulfurous gasses; too high and the reaction will be slow or non-existent. You might try adjusting the pH up to about 3.5 to 5.0 and add the metabisulfite.

Chromic acid (Cr+6) has a very strong amber color whereas Cr+3 has a faint greenish color, so you may be able to use color as well as ORP (oxidation reduction potential) readings to know when all of the chromium has been reduced. After that, it's a matter of neutralization with an alkali like magnesium hydroxide or lime to a good pH for precipitation.

It should go without saying that this procedure should be done on a beaker sample under a lab fume hood several times until you are completely confident of the amounts of reagents to add, and whether excessive fumes are given off, before you consider treating a production size batch. Here in the USA only chemically knowledgeable people who have received hands-on haz-mat training would attempt neutralization of etching waste. I'm not sure what the regulations are in Maharashtra. Good luck.


Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


Q. I run a plating plant on ABS plastics (Cu, Ni, Cr). The current etching process we are using is that of Chrome and H2SO4 at 65-70 °C followed by electroless Ni. However, there are a lot of drag-out losses in etching and hence much waste water to be treated.

Is there any other type of etching, maybe an organic etching like acetone, which can be used? If there is, what are the concentrations and specs for it.

Also my electroless Nickel tank sometimes gets unstable. I use a ratio of 3:2:1 of nickel sulphate; sodium hypophosphite and citric acid, and set the pH using ammonia, with a Pd sensitization and HCl Accelerator before. Is there something wrong with the composition, if yes, please recommend.


Rahul Kakkar
Electroplating on plastics - New Delhi, Delhi, India

Electroless Plating
by Mallory & Hajdu

from Abe Books

A. Some large shops use gaseous etching for ABS, Rahul, but it's a substantial capital investment.

Please consider getting a proprietary electroless nickel process from one of the suppliers who have invested countless R&D hours in the effort. Reliable plating on plastic from a home-brewed electroless nickel formulation is a challenge I wouldn't want to undertake, thanks :-)

These days direct metallization (with graphite or organo-metallic proprietaries) is also gaining popularity over electroless processes for metallizing plastic. Good luck.

Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

September 27, 2018

Q. Hello,

We have issue with our etching bath, because there is no foam.
We use wetting agent, but we still can't get foam.
The etching bath is 5 years old.
Is it possible, that etched butadiene covers the surface of the bath?
And if that's true, how can we clean it?

Andrew Wilcox
Technologist - Berlin, Germany

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