Algae, fungus, bioslime in plating tanks?

A. I found reducing exposure to sunlight on rinse tanks slows down algae growth.

A. Hi Travis.
Jacob H. says below that small additions of thymol [thymol crystals on eBay or Amazon [affil links] solved the problem in his citric acid based rinse tanks. I can't guarantee that it will work in your cleaner but I would be quite confident that it will not interfere with the workability of your cleaning solution.
Luck & Regards,


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

A. Hi Travis,

You're the first person I've come across running this bath. Which is my favorite one on the passivation line, by the way!

Code N: Bioslime Method.

Per Specification: "Tank shall be cloudy with a dull pale peach-brown loose slime that builds up in the tank corners. Tank must be covered or otherwise obscured from view when anyone wearing a necktie is within 20 feet."

In all seriousness, though...

Parts processed through my slimy Code N bath as a passivating solution (even though it's originally written for 'cleaning') still pass 24h water immersion, no matter how nasty it gets. I just looked back and discovered we haven't fired up our old 416 tank since early 2021 as we fell in love with the algae health smoothie! It's absolutely trouble free. And vaguely disgusting.

The only reason I'd be concerned would be if you find bits clinging to your parts after rinsing. And you'll surely have changed out the tank well before it gets to that point anyway.

Just give it an occasional runaround with a sieve or a pool skimmer, depending on bath size, between dumps. I'm only half kidding.

The bad news is that the gentlest tanks grow the most abundant microflora. Don't get me started on RoHS ChemFilm lol.

The good news is that being an organic acid, you're likely to be able to get away with a variety of organic biocides, moreso than in a Nitric bath.

The one I use in my organic dye tanks would be worth a shot. It's Acticide-CT.

Bucket test, of course!

But I'm quite serious that the process is super forgiving. I was also surprised :)

Rachel,
LOL, good one!

Agreed, organic biocides work well in citric acid baths. I have heard of other methods such as UV lights, as well.

There's a reason that the ASTM A380 code N solution is not listed as a passivation bath: it's not. ASTM A967 makes it clear that 4% citric acid is necessary for a passivation bath, and the 1% citric for code N does not qualify. Though yes, many stainless parts are able to pass one or more of the passivation tests without a proper passivation treatment, if they are a good grade and don't have any contaminant iron on the surface.

Hi Ray! Glad you showed up for this one :)

You of course already know, but I'm putting it on record again for the Visiting Team, that the Citric baths are extra forgiving even as they age due to their chelating properties- rendering the stripped free iron unable to react with / contaminate subsequent loads.

I've been pleasantly surprised by the range of alloys that like it! Caveat: we vapor degrease most of the stuff going in there, then run it through alkaline aqueous ultrasonic cleaner, prior to processing. Put the best foot forward, right?

That old "cleaning" spec mentions saltpeter as a surfactant. I make up the tank with equal weight dry citric and sodium nitrate, and just run it on a free-acid test until it's too cruddy to deal with, no saltpeter adds as I assume it's not significantly consumed in process... though the environmental analytical chemist in me keeps looking at free nitrate as bioslime buffet... yummy!

For the cost of makeup and disposal, its a cheap buffet, beats the Golden Corral by a landslide, and less likely to give ya indigestion :)

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.

"Gold Plating Technology"
by Reid & Goldie
(hard to find & expensive; if you
see a copy cheap, act fast)


on eBay or

AbeBooks

or Amazon

(affil links)

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

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!

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 [thymol crystals on eBay or Amazon [affil links] 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.

A. Hi Carolyn,
Jacob hasn't been around in a while. I haven't seen a specific protocol for making a thymol solution from thymol crystals [thymol crystals on eBay or Amazon [affil links] , but thymol is commercially available as a diluted disinfecting solution [thymol disinfectant on eBay or Amazon [affil links]
Luck & Regards,


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

Hi, Chung. Bring a dust cloth with you and 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 our 'Finishing Technology Hotline' from 1991 which discusses the fungicides you are asking about. Good luck.

A. Hi, Sam.

Your question was discussed in this forum before the public Internet even existed, believe it or not :-) Please see: "Algae Growth in Gold Plating Rinses" from our electronic BBS days.

Regards,

A. Common help is very fine filtration, UV light exposure, Frequent tank dumps and finally antibiotics.

A. First, never put a filter on the inlet side of any pump, especially a 1 micron.
Your filter will probably last at least twice as long on the outlet, as well as the pump will not be killing itself when it cavitates.
Till you get the bulk of the bad stuff out, it will just exponentially grow.
On a weekend, put a large 10 micron filter on the outlet. Later in the day, put another one on for all night. The next morning put a 5 micron filter on it. That night put another one on it, or if you feel good about it, put a 1 micron filter on it.
By a large filter, I mean one that is 5 to 10 times larger than the one that you are using.

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

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.

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 ⇦ bleach/sodium hypochlorite in bulk on eBay or Amazon [affil links] , 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 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 Hampshire, England

A. Hi All,
I'm a process engineer and part of my responsibility has been to set up a pure/soft gold rack electroplater, and to do the process development to start producing parts. Anyways, we also had a lot of problems with fungus in the first drag-out bath. By adding an immersion heater to the drag-out bath, we drastically decreased the fungus growth. We simply turned it on once per day, waited until the water reached about 140 °F, and then turned it off. Immersion heaters are pretty cheap.