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"What chemicals or processes are used to Strip gold plating?"



Current question:

November 4, 2021

Q. Hello Ted, It has been too many years since we talked. We are the few left from the circle Garden State Branch or Chicago Branch AES. I was looking for the proprietary stripper for gold from copper. When I saw this, I had to stop to say HI! God Bless my FRIEND! As for the stripper, I do not recall supplier. I want to remove gold from copper without attacking the copper. Thank you!

Tom Reynolds
- Bellefontaine, Ohio
^


November 2021

A. Hi Tom. So nice to hear from you! Between a general diminishing of our industry and father time claiming some of our mutual friends, it is starting to get a bit lonely for this old-timer :-)

Most gold strippers are cyanide-based but there are some cyanide-free ones. Gold Touch [a finishing.com supporting advertiser] offers an electrolytic one you could look into at goldtouchinc.com/product/tivastrip-free-quart/

Stay well and stay in touch. old friend :-)

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
^




Closely related Q&A's, oldest first:

1996

RFQ: I am looking for a mild solution to strip gold. There used to be a product called "Orostrip" which was sold in a dry form and upon dissolving in water adding cyanide, it worked very nicely to strip gold layers from semiconductors without damaging the substrate.

Does anyone know where to get it or how to prepare this ?

Gerko Oskam
university - Baltimore, Maryland
^

^- Sorry, this RFQ is outdated
     View Current RFQs



A.

"ORO : as a prefix with various endings, gold plating solutions, chemicals, and supplies, Technic" -- from the Metal Finishing Guidebook Tradenames section.

tom & pooky   toms signature
Tom Pullizzi
Falls Township, Pennsylvania
^


A. A straight KCN solution heated will strip Au from substrates. The Orostrip from Technic has an accelerator for KCN solutions.

Another thin film supply house on the East coast had a similar product but I forget the name of the company (it has been years since I've dealt w/ this).

Another way to strip Au is to use a heated solution of KI:I:H20. This chews Au quickly but is very corrosive to many metals (and you can see the Iodine fumes rise off the heated surface).

Jeff Albom
- El Granada, California
^


1996

A. Every gold process supplier sells a gold stripper. If you put it on chances are you'll occasionally have to take it off too!

I have used LeaRonal Super Strip 100 for years, but the Orostrip works good too.

Most of the strippers are based on a solution of sodium or potassium cyanide and an organic oxidizer like meta-nitro benzoic acid.

bill vins
Bill Vins
microwave & cable assemblies - Mesa (what a place-a), Arizona

^


1996

A. Enthone-Omi has a product named Circuitprep NX to which you have to add KCN.

sara michaeli
sara michaeli signature
Sara Michaeli
chemical process supplier - Tel-Aviv, Israel
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Ed. note, August 2021: We thank these participants for their postings, but we've learned a lot about what works and doesn't work in a public forum in the last 25 years. Also, the Internet has changed dramatically with intelligent spambots which now scan all forum discussions like this, relentlessly trying to post advertisements or alert humans to do so. So we no longer publicly post brand & sourcing suggestions ( huh? why?). Commercial suggestions in private only please, and only if the poster has posted an RFQ requesting private contact.





To minimize search efforts and to offer multiple viewpoints, we combined previously separate threads onto this page. Please forgive any resultant repetition, failures of chronological order, or what may look like readers disrespecting previous responses -- those other responses may not have been on the page at the time :-)



Potassium Cyanide gold stripper and air sparger

January 19, 2011

Q. I am stripping base metal parts with deposits of gold using a Potassium Cyanide based Stripping solution. We began sparging air into the baths to increase the rate of gold dissolution successfully for a while now. However, we recently noticed the generation of hydrogen cyanide from some of the baths when the stripping process is near completion. A fresh bath with the same parts does not indicate HCN. It only seems to occur when the stripping has died off, when most of the KCN has been converted to the metal salt complex.

The only time this has ever happened prior to sparging, was when the pH dropped. In the case of sparing, the pH has stayed above 11. I see nothing in the chemistry that says excess oxygen would somehow cause the generation of HCN. What am I missing?

Doug Bouldin
Industry - Phoenix, Arizona, USA
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January 20, 2011

A. I would expect that your fume is something other that HCN, but in any case, you should use a pump to agitate instead of air. I limit air sparging to rinse tanks and tanks with very dilute chemistry. Air sparging always increases emissions.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri
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February 14, 2011

Q. Thank you for your response. I am pretty confident that it is HCN. I check for possible interference with the detector tubes and there is none that we have. I have found a possible air contaminant, CO2, that consumes potassium, forming a carbonate and HCN. Not sure that is what is occurring, but seems the only other explanation.

Regarding sparging and air emissions, you indicated it increased your emissions. Which emissions? Also, what are the emissions from the tank with no sparge and no heat? If we use potassium cyanide, wouldn't the solids concentrate in the tank as the water evaporated? Is there an evaporation equation with respect to KCN emissions?

Thanks again.
Doug

Doug Bouldin [returning]
- Phoenix, Arizona, USA
^


February 15, 2011

A. Hello, Doug. In a sufficiently alkaline cyanide solution, HCN is just not going to be present either in the solution or in an emission because HCN is an acidic form of KCN. While it is true that CO2 can behave as an acid, it is neutralized by the alkaline species in your solution long before the solution becomes acidic enough to allow the HCN to exist. Since it doesn't form in the solution (except perhaps as a very short-lived intermediate), it is not a potential emission as a vapor. All you need to do to ensure that you don't evolve HCN is to check your pH at regular intervals. Also, KCN will not have an emission because it does not form molecular vapors from aqueous solutions. What you do have is ammonia. Ammonia is generated from the natural hydrolysis (reaction with water) of all solutions that contain free (non-complexed) cyanide. Basically, cyanide reacts (breaks down) with water and ultimately forms ammonium and formate ions slowly over time. The reaction rate for cyanide hydrolysis is only a function of time and temperature. Some of the ammonium ions in solution (NH4+) will further react to form an emission of ammonia (NH3) gas. The amount of this emission is related to the pH, the temperature, and air agitation. Increasing any of those 3 things will increase the emission, but the reaction still happens with no additional heat and no sparging. In general, air agitation increases emissions for any chemical that emits a vapor though not all emissions are harmful (example- water vapor). Evaporation does concentrate the solids in the mixture, but the water holds an amazing amount of KCN before it will become saturated and settle out on the bottom. Part of your chemical solution control should be to monitor and maintain the solution level for this reason. I hope this helps to clarify things.

Jon Barrows
Jon Barrows, MSF, EHSSC
Independence, Missouri
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February 17, 2011

thumbs up sign Jon, Thank you very for your response and insight. I have a regulator wanting me to provide emissions of cyanide compounds from our strip tanks. He directed me to use the evaporation equations in AP-42. I was beside myself knowing that solids do not evaporate with water from an open tank, unless agitated and carried away as bursting bubbles, yet he insists we provide cyanide compound emissions.

Our sparging is experimental to keep the chemistry mixed and the appearance of HCN was not expected, especially since pH is maintained above 12.

It is always nice to confirm with others to ensure I was not missing something. Thanks again.
Doug

Doug Bouldin [returning]
- Phoenix, Arizona, USA
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February 28, 2011

A. Hi Doug
Jon has covered the situation really well. Just a couple of practical suggestions re stripping is that you do need some oxidising potential to strip. Suggest you use an aquarium type bubbler to aerate, not vigorous air, and/or alternatively add 0.2-0.5 ml per liter of hydrogen peroxide well diluted.

Geoffrey Whitelaw
Geoffrey Whitelaw
- Port Melbourne, Australia
^

adv.
Metalx nickel stripper

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