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topic 5358

Bio-Fouling of Gold Plating Rinses

A discussion started in 1991 but continuing through 2018


Q. I am looking for additional ways to control bio-growth in rinse tanks after gold plating. This has always been a problem with acid gold plating baths, and I have seen a number of control methods through the years.

Our current cleanup is to dump and scrub down the rinse tanks (non-abrasively). We have also added 0.2 micron filters on the incoming water.

Other shops I have worked have used bleach to leach out the rinses (not during production!). One of our people says the growth proceeds upward from the drain to waste treatment. We can't dump bleach down the drain because it goes to a resin system.

Our gold is high purity, for wire bonding, so we really can't afford to put biocides in the plating bath or rinses.

Any contributions will be greatly appreciated.

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


A. Will UV light work?There are a few lamps made for direct immersion and I thought some people put a lamp over the tank at night. No, I have never done it.

James Watts
- Navarre, Florida

Gold Plating Technology
from Abe Books



A. Bill,

I am a QA manager of a plating shop and I am (or I was) a microbiologist so I can try to give you some answers.

1) your system (clean up of tanks) may be effective only for few hours (12-24) because microorganisms have a very fast growth rate.

2) the 0.2 micrometers filters on incoming water can only reduce the initial quantity of microorganisms in water, but consider that: - the rinse tanks are put in the open air - contamination occurs on the surface of tanks - the velocity of growth of microorganisms makes this filtration useless.

3) if you wish to solve this problem, you have to control the growth of microorganisms in some way: the use of sodium hypochlorite or other biocides is the best solution (microbiological point of view)

4)if it is possible, verify the type of bio-growth (algae, bacteria or fungi)and perform the microbial count (No. of microorganisms per mL); you have to ask to some microbiological laboratory to check this.

5) There are many simple systems to do the microbial count in house (dip tests); you may do this test on a fresh rinse bath and every day (or every two days) for a period of time (1-2 weeks); you can define some acceptance limits and when the microbial counts exceeds limits, you can dump the rinses.

I hope it will help you Franca Assone

Francesca Assone
electroplating shop - Torino, Italy


A. Just a thought. Could bubbling ozone in the tank work? I do not know its effect on the chemicals nor do I know the source of bottled ozone, however!

Mandar Sunthankar
- Fort Collins, Colorado


A. We experience the same issue occasionally. Clogs up our gold recovery system and is a mess to sanitize again. We've found that adding a little Thymol to the rinse inhibits microbial occurrence/growth quite effectively with just a small addition (usually to the non-flowing drag-out rinse). 20-30 mL for a 10 gallon drag-out rinse is plenty. Lasts for weeks or even longer. No effect on our deposits has ever been observed. Hope this helps.

Jacob Hendrickson
- Seattle, Washington, USA

April 4, 2012

Q. Jacob: What type of Thymol would you use? I read that the crystalline form of Thymol is only soluble in alcohol and acetic acid, so would you use a different form of Thymol, or a different preparation method?

We are having trouble with moderate amounts of Bacteria ("fuzzies")in our Gold Dragout Tanks. Its a fairly small Tank (20L), and we treat it every week with a proprietary solution from an outside vendor, but it does not seem to help. We have tried both polypropylene and carbon filters on the Tank, but both seem to get easily filled with bacteria. A small addition of hydrogen peroxide does seem to help, but we would rather control the problem then have to act retroactively once there is a significant amount of bacteria. Is there any in-house remedies we could possibly try as to help eliminate and control the bacteria content within the tank without compromising the gold solution?

Thank you in advance,

Carolyn Pokora
- Rochester, New York, USA

Ed. note: Jacob hasn't been around in a while, Carolyn, but hopefully another reader will help out.

* Meanwhile, take a trip down "Memory Lane". Before there was an Internet, people dialed up through a modem and posted Q&A's on Electronic Bulletin Board Systems (BBS's). Here's a discussion about biological growths in gold plating rinses from 1991 :-)

Large 'nodules' on gold rinse filter

May 8, 2017

Q. Hello all,

Chemist for an electroforming shop here. We've been having some issues with our gold rinse tank -- cyanide gold, acid (4.8 - 5 pH). Our rinse tank seems to get a lot of "bugs", especially over the weekend. I'm not sure if these are microbial, or something else. The assumption is they're organic, and we've been trying to treat it with H2O2 or HCHO. Nothing really seems to work. We tried a proprietary chemical (Fungicide G) and it didn't work either.

This past weekend, we came back to see large "beehive" nodules on our filter.

Any clue as to what's going on? Any ideas on how to fix it?

This chemistry has little to no phosphates, is a citric acid based cyanide gold tank. Little else is in the tank besides these chemicals.


Brian Minchen
Plating shop chemist - Rochester, New York USA

May 10, 2017

? Hello Brian, is the rinse tank connected to a "gold bug" or resin column?"

Mark Baker
Process Engineering - Phoenix, Arizona USA

June 29, 2017

A. If I am not mistaken, it is the citrate in the gold plating solution which helps the growth of white fungus in the drag-out tanks. Using other complexing agents instead of citrate will solve the problem.

lee leong tee
leeplating company - malacca, malaysia

February 16, 2018

Q. Hello

I work as a gold plater and currently there is a lot of green algae contained within the yellow gold tank. I plate onto sterling silver and sometimes it comes out slightly dark, or grey or just dull, despite having thoroughly cleaned everything in acid. I have read with interest information using activated carbon in a mesh sock hung over the side. Or using a fish tank filter? There is nothing in place at the moment to remove any of the algae. The water colour is dark green and not very pleasant. Please can somebody recommend what I need to do to get rid of the algae?
Many thanks indeed

Deborah Rose
- Brighton. East Sussex. England

simultaneous February 17, 2018

A. Hello Deborah, you didn't mention if you had continuous filtration which would give you solution agitation. Algae forms quicker with a stagnant tank. When I worked for a precious metal supplier we did have a algaecide that you could add to the tank. I would pump out the tank, filtering into a clean, leached tank. Clean your main tank using a little bleach scrubbing the walls and anodes well. Be sure to rinse the tank very well before pumping the gold bath back in. Plating equipment suppliers can set you up with a filter system that is sufficient for your tank size. These systems also take carbon filter tubes as well as polypro filter tubes. It would be beneficial to run carbon packs for 2 hours a week. I haven't ever used a carbon sock and be careful if you have to go that route. Passing the bath through a carbon sock has to be continuous for 3-4 hours. Be sure the sock has a micron rating of 5 micron or carbon will be released into the bath. Don't use powdered carbon, but a high grade granular type. So to sum this up, buy a filter system if you don't currently use one. Run the filter system the whole day your shop is open. Run a carbon pack once per week for 2 hours. Check with your gold bath supplier for an algaecide. Hope this helps.

Mark Baker
Process Engineering - Phoenix, Arizona USA

February 17, 2018

A. Hi Debs
There are a number of broad spectrum biocides that might do the job but you have no idea of the correct dosage or what effect they might have on your solution. You could make the situation a whole lot worse.
You should speak to your process supplier. They have a team of specialists who know their product and have a keen interest in keeping their customer's process operating efficiently as they want your continued business. The suppliers I know will probably send in a technical rep to take a sample and advise. You may well find that the effect you see on the deposit have nothing to do with your algae problem.
It costs nothing to ask !

geoff smith
Geoff Smith

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