# High cobalt level in solution



## johnleivers15 (Feb 7, 2015)

Hello everyone,

Could somebody point me in the direction to fix this problem not looking to be told I don't mind the read. We use a 40 ltr bath which I monitor throughout the day. I check the dosing system, PH and the gold content of the bath. Optimum is 4g/l of gold, PH of 0.6 and a recommended cobalt level of 500. As far as the 500 is concerned I am not sure, 500 grams/mils/ounce? of cobalt per 40ltr/1lter/mill? it dose not say. Anyway its at 700 odd. I cant see it making any impact on the plating at the moment but might it ? I have tried a partial replace mix of 5 ltrs but not much difference. Cobalt is the only thing I cannot measure for that I send a sample off to be Analise every 2 weeks. I get a report back but no definite remedy to correct its level.


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## FrugalRefiner (Feb 7, 2015)

If I recall some of GSP's posts correctly, cobalt is used in gold plating as a hardener. Try a search for cobalt with goldsilverpro as the author.

Dave


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## goldsilverpro (Feb 9, 2015)

johnleivers15 said:


> Hello everyone,
> 
> Could somebody point me in the direction to fix this problem not looking to be told I don't mind the read. We use a 40 ltr bath which I monitor throughout the day. I check the dosing system, PH and the gold content of the bath. Optimum is 4g/l of gold, PH of 0.6 and a recommended cobalt level of 500. As far as the 500 is concerned I am not sure, 500 grams/mils/ounce? of cobalt per 40ltr/1lter/mill? it dose not say. Anyway its at 700 odd. I cant see it making any impact on the plating at the moment but might it ? I have tried a partial replace mix of 5 ltrs but not much difference. Cobalt is the only thing I cannot measure for that I send a sample off to be Analise every 2 weeks. I get a report back but no definite remedy to correct its level.



I would guess that it's 500mg/liter or 0.500g/l or 500ppm - all the same thing. I've never dealt with a gold bath with a pH as low as 0.6. All of the Au/Co hard gold acids baths I've run (maybe 1000) had a pH of around 4.2. Who manufactured the bath and what is it's "name"? 

The only way excess cobalt could get into the the bath would be that you added it. I assume cobalt is in the gold replenisher. If so, it is building up because it's not plating out as much as it should.


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## johnleivers15 (Feb 9, 2015)

Company I work for purchased the system from Balco http://balco.co.uk/ . We use Auruna 311 gold solution http://www.schloetter.co.uk/plating-processes/gold-process.htm & cap 50 from the same suppliers. I cant find the cap 50 on there website anywhere though. Replenishing is done through the dosing system it will run for x amount of time every x amount of amp minutes. Each has there own dosing times. The cap 50 I think is causing the high cobalt level so I lowered the dosage but it hardly made a difference so i turned it off. Seems to be very, very slowly coming down. Its a newish system which I have to get the hang of and eventually ill get the balance right. I wasn't sure if there was a quick fix other that wait it out or a new mix but at 40ltr they wont be happy and it dose not seem to be affecting anything yet :shock:


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## johnleivers15 (Feb 9, 2015)

The system


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## dannlee (Feb 9, 2015)

I got curious & invested a little free time, the 311 data sheets turned up...

*AURUNA® 311 Gold Cobalt Electrolyte* (0.3 weight % Co 99.7 weight % Au)

http://www.umicore-galvano.com/images/stories/downloads/en/Umicore_AURUNA-311_EN.pdf

AURUNA® 311 Initial Concentrate MSDS content list...

sulfuric acid 15%
phosphoric acid 30%
cobalt sulphate 1.5%

http://www.plachemco.com/images/AURUNA® 311 Initial Concentrate.PDF

_"AURUNA 311 is also available as a cobalt-free special version"_ might lead back to the 311Cap50 solution that has nearly zero presence on the web...
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Oh - and thats about the sexiest plating line I've ever seen - visible wiring details (or lack thereof) are a good model for anyone's projects. STAY SAFE!


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## johnleivers15 (Feb 9, 2015)

I cant see why they would give us both types? And yes the cap 50 I could not find at all not even on there own website. It don't look so good from the back :lol: I need to have a good cleanup :roll: thank you very much for the find.


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## goldsilverpro (Feb 9, 2015)

dannlee said:


> I got curious & invested a little free time, the 311 data sheets turned up...
> 
> *AURUNA® 311 Gold Cobalt Electrolyte* (0.3 weight % Co 99.7 weight % Au)
> 
> ...



Dannlee,

I found the 2 same links this morning but I read the information a little differently than you did.

The MSDS is for the replenisher (see the heading of the PDF), not the initial, or makeup, concentrate, as you stated. The initial makeup solution very likely has the same ingredients (although probably in different proportions) as the replenisher plus other things, such as a wetting agent or maybe an organic brightener. I could find no reference for the makeup solution. According to the MSDS, the 500ml of replenisher in the bottle contains 100g of gold, 15% H2SO4, 30% H3PO4, and 1.5% cobalt sulfate. Whether the %s are w/w, v/v, or w/v, I have no idea. I would guess the acids are v/v and the CoSO4 is w/v.

The .3%Co/99.7%Au is not the electrolyte makeup as you stated. In the Umicore brochure it says the deposited alloy is .3% cobalt and 99.7% gold.


johnleivers15

In the old days, the companies that sold plating solutions provided many free services to their customers, such as free bath analysis and free troubleshooting of bath problems. Today, these services have dropped off somewhat but surely they are there if you need them. Your solution is manufactured by Umicore, a huge PM company, and is sold through a vendor. I would call your vendor and explain the situation. If you talk to the right person, I guarantee you will get good answers. If possible, try to talk to a technical person.

I can see why the pH is very low, 0.6. The acidity enables the gold to be plated directly on stainless, without need of a Wood's nickel strike (high nickel chloride and HCl).

I am very curious as to what gold complex could be used in a highly acidic bath. I don't think it's potassium gold cyanide or sodium gold sulfite, the 2 that make up about 99+% of all the gold baths in the world. I doubt if it's a ferricyanide or a chloride. My guess would be that it's a phosphate gold. A company I worked for bought a patent from a guy that had invented a series of phosphate color golds, so I know they exist.

I never liked replenishers with both Co and Au in them. I would prefer a replenisher with everything but the cobalt sulfate in it and a separate container of just cobalt sulfate solution. I would then setup to analyze the cobalt in-house. I think it's just a simple EDTA titration. Much better control. A plating bath changes a little each time you use it. These changing variables can affect the amount of cobalt co-depositing with the gold. Obviously, since the cobalt level is increasing in the bath, less cobalt is co-depositing. About the only thing this would do would be to decrease the gold hardness. It you need that hardness, you have a problem. However, don't swing to the other side because excess Co in the deposit can cause brittleness and cracking. Before doing anything, call the vendor. I would call them anytime I had a solution related problem. They know more than anyone about their products.

What exactly is Cap50?


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## johnleivers15 (Feb 10, 2015)

My mistake the cap 50 is the gold solution the 311 is replenisher, as for chemical analisys the company we buy from do this for free I send them a sample every two weeks just to make sure my reading on x-ray are correct. My readings are always bang on apart from the cobalt because I cannot detect it with a wet sample. We have brought the cobalt issue up and it seems they dont have a definate answer or arnt interested so its just trial and error it will be right it will just take time. Thanks for your help with this.


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## Geraldo (Feb 10, 2015)

Not trying to be a jerk, but if your system vendor isn't providing sufficient technical support, why don't you contact Umicore directly?

I have done that in the past for other things, while working for one of their competitors (Teck). While they didn't want to give out proprietary information, they were certainly willing to discuss general technical topics. I had several useful conversations with folks there about subtle aspects of chemistry, for example.

Don't contact their sales, marketing or managerial folks. They don't know anything and are paranoid (in every organization, not just Umicore). You want to contact a knowledgeable engineer or chemist. Google should let you find scientists/engineers working to develop these plating technologies. Tell them that you are running their system and need to understand it. Make sure you get straight to the point and communicate that you only need a couple minutes of their time. In my experience, competent engineers and chemists are very happy to educate you.

Just a thought.


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