# Need Help with Gold Recovery from Gold Plating Process



## CarolineSun (Apr 25, 2014)

Hi,

I am very new with gold plating and I really need some help. Thank you in advance!

Our client does gold plating and they think they are losing gold into the exhaust air. Could you think of any reason that would happen? Anybody had similar problem before? I couldn't find any article say they recover gold from air exhaust. 

I know gold is ionized in the plating bath, but when a solution vaporizes, the solute mostly left behind except for those volatile compounds. So I would think gold is not likely to present in the exhaust air. So, how would gold migrate from plating bath to air stream?

I look forward to hearing from you!
Thank you!


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## nickvc (Apr 25, 2014)

Personally I doubt the gold plating solution is releasing much if any gold into the exhaust unless they are boiling the solution. Loses from plating solutions may be in the rinse tank or the polishing shop if they finish the goods after plating, the wires used to hold the goods will also be a likely place to look or the racks used to hold the items,also possible is that the amount been plated hasn't been calculated properly. The pipes from the exhaust system should be easy to test, wipe one out and treat it, be careful and find out if it's a cyanide or acid plating solution before messing with it.
Good luck with this and keep us up to date on your progress on solving this problem.


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## goldsilverpro (Apr 25, 2014)

May I ask what function you perform for them?

With any gassing at the anode or cathode, bubbles coated with plating solution can escape into the air, but I would doubt that this is the problem unless the gassing is severe. Why do they think the gold is being lost into the air? Analysis? How is the gold analysis being performed?

Is it possible that an employee is stealing solution from the bath? I've seen this happen a number of times. Also, I've seen employees plate their own objects on the sly.

What type bath are they using: alkaline cyanide, hard acid cyanide, or sulfite? What type parts are they plating? How large is the bath? What is the nominal gold concentration of the bath? When was their last complete bath analysis? Are they plating by voltage or by current density? How thick are the gold deposits? Are all the ingredients in the bath (especially the gold) constantly maintained in their proper ranges? Are there any particles on the bottom of the tank?

Ask them if they ever use carbon filters- the carbon will adsorb gold. Also, if they use an acid cyanide bath and the pH is too low (below about 4), gold compounds can precipitate and be picked up in the filter.


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## Lino1406 (Apr 26, 2014)

Check also gold content in the original feedstock


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## 4metals (Apr 26, 2014)

Back in the '70's I ran a large captive plating shop processing electrical connectors. Out of no-where the accountants came up with the notion that we were spending too much on gold. 

We installed some devices called "Gold Cash Registers" which were basically ampere meters to track how much power went through the baths. Based on the assumption that the total amperes used is directly related to the quantity of gold deposited. While that is true, all of the gold does not end up on the parts being plated and things like racks and danglers and small parts baskets also take their share of the deposit. Not to mention Joe the platers motorcycle! 

The gold is likely not in the ducts in any appreciable quantity, the fine mist at the anodes and cathodes can be sucked up by an overly strong exhaust but that is the rare exception. 

Accurate calculations of surface areas and tight tolerances for plating thickness are required to account for all of the gold on product, then there is the gold that accumulates on the racks and motorcycles. in the end the accountants weren't happy with the "Gold Cash Registers" anyway.


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## goldsilverpro (Apr 26, 2014)

4metals said:


> Back in the '70's I ran a large captive plating shop processing electrical connectors. Out of no-where the accountants came up with the notion that we were spending too much on gold.
> 
> We installed some devices called "Gold Cash Registers" which were basically ampere meters to track how much power went through the baths. Based on the assumption that the total amperes used is directly related to the quantity of gold deposited. While that is true, all of the gold does not end up on the parts being plated and things like racks and danglers and small parts baskets also take their share of the deposit. Not to mention Joe the platers motorcycle!
> 
> ...



Those are amp-minute meters that are used for gold and other PM plating. They use amp-hour meters for such things are nickel or copper plating. The amp-min. meters keep track of the total accumulated amps X minutes. Some can be locked so the platers can't reset them. These meters are used to keep track of how much gold is being deposited on the particular parts they're plating, knowing when it's time to add more gold to the bath, and to help keep the platers honest.

In the case of alkaline cyanide gold baths, plating steadily occurs a little under 100% efficiency of 0.122 grams of Au/amp-min. The efficiency of a Ni or Co hardened gold acid cyanide bath, however, is about 30%-45% and that can vary if the variables change (which they always seem to do daily or sometimes hourly). 

The main reason I asked CarolineSun all those questions was so I could get some sort of a fix on the potential variability of the plating efficiency in their system. That could be their whole problem.

Another question I asked is whether they plated by voltage or by current density. Plating by current density is using so many amps per square inch for an exact amount of time. If they are plating by voltage, they set the voltage and then they may examine the parts every so often to see what they look like. If they don't look right they may adjust the voltage and leave it in awhile longer. Color gold baths, used for plating very thin deposits of various karat colors on cheap jewelry, are usually plated by voltage for times less than 60 seconds. If the company is keeping the bath up to snuff with frequent analysis and additions, the parts will all look the same after, say, 45 seconds or whatever. If they aren't keeping the bath right, it's hit or miss and they could be be staying in the tank too long and thus plating more gold on the parts than they they think they are.

Plating shops, like amateur gold refiners, tend to shy away from analysis and it constantly gets them in trouble. As 4metals knows, I worked for Sel-Rex, who was, at that time, the world's largest seller of gold plating solutions. One of my jobs was to troubleshoot plating problems for the some 1500 companies that were using our solutions (mostly L.A. aerospace companies and Silicon Valley electronic manufacturers). I probably got 10-15 phone calls each day on problems. I would estimate that 80% of these problems were simply solved by the customer getting a full bath analysis and then adding the needed chemicals (or, by adjusting the pH to the proper level). I look at plating solutions as living things that constantly change. What works good today can work poorly tomorrow.


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## Westerngs (Apr 26, 2014)

I don't have any experience with plating baths, but many years with gold and silver refining cells. The average temperature for the electrolyte is about 150F. The wet scrubbers for both processes always build up gold and silver in solution. We drain the scrubber tanks to wastewater treatment twice a week. The wastewater treatment sludge always contains both gold and silver for which we get paid for by the copper smelter, in addition to the copper. 

We do run our exhaust at a pretty high velocity, around 150 cfm, knowing that we will collect gold and silver in the exhaust, but will recover a percentage of it in the wet scrubbers.


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## 4metals (Apr 26, 2014)

> Plating shops, like amateur gold refiners, tend to shy away from analysis and it constantly gets them in trouble.



My first job in the electroplating field was on a night shift for a relay manufacturer and I did all of the analysis of the baths. When I finished graduate school I left and went to work for a mil-spec connector company running a plating shop. They had major problems with quality so I started off on a strict analytical regiment and the problems just went away. When you have decent platers and you give them consistent chemistry to work with, a lot of the bumps in the road just go away. Electroplating is a combination of art and science, I assured the chemistry was right (which knocked off the science end of the equation) and the platers were the artists. 

I was on Long Island and Lea Ronal was right around the corner so I never used Sel Rex chemistry. (sorry Chris!)


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## goldsilverpro (Apr 26, 2014)

4metals said:


> > Plating shops, like amateur gold refiners, tend to shy away from analysis and it constantly gets them in trouble.
> 
> 
> 
> ...


A long true story.

In the early 80's, I consulted for a guy who owned a medium sized company that mainly was brass plating lamps. He had a big contract but couldn't plate them fast enough and was in danger of losing the contract. If I remember right, he had a 1000 gal cyanide brass tank and ran probably 30-40 lamps at a time. After plating, they were dipped in a dark antiquing solution, dried, and then buffed to raise the highlights of the brass on the high points. He ran 2 shifts, an 8AM to 4PM shift and a 4PM to midnight shift. The prima donna super star platers were on the day shift.

The owner was from Lebanon. Over there, the national game was Backgammon. I considered Backgammon my game and, during the lunch hour, we had some great games, for money, of course. Our game philosophies were totally opposite. He was a runner (offensive) and I was, at that time, mainly a back game player (defensive). I think I barely won the majority of the games but good persistent runners can really put the pressure on and are very hard to deal with, especially when they get good dice rolls. 

A cyanide brass bath consists of copper cyanide, zinc cyanide, Na or K cyanide, Na or K carbonate, and some organic additives. Depending on the concentrations of these, the applied current, etc., the color of the deposit can range between white (too much zinc in the deposit) and red (too much copper). The ideal is that perfect yellow brass color. Brass, or any other 2 metal alloy, is very tricky to plate. A 3 metal alloy is almost impossible.

It took a couple of days to find out what was going on. First, the bath hadn't been analyzed for probably months. Second, all the platers plated visually by feel. They set the voltage and then, after awhile, pulled out a few parts. If the color wasn't right, they fiddled with the voltage and plated longer, and longer. 

I talked the guy into spending a few hundred dollars to set up what was needed to analyze the bath. Once set up, I started coming in at night and spent my time with the "inferiors" on the 2nd shift. I got very close to these guys and gals. They treated me like a king and they fed me some great Mexican food that they always cooked on hotplates. I analyzed the bath and added the required chemicals to bring the bath up to snuff. I stopped the plating by voltage on the 2nd shift. I calculated the surface areas of the lamps and we simply ran the proper amperage (current density) for an exact amount of time, no more, no less. Everything we plated was that perfect yellow brass color and of the proper thickness. The first night we did this, we literally doubled the production of the first shift. We repeated it the second night. The main honcho plater on the first shift then threatened the owner with a strike of all the 1st shift employees if I wasn't fired. They were embarrassed and had lost "face." The owner apologized to me while he was firing me. I have no idea what happened after that. I've always wondered. I was there for about a week total.


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## goldsilverpro (Apr 27, 2014)

Westerngs said:


> I don't have any experience with plating baths, but many years with gold and silver refining cells. The average temperature for the electrolyte is about 150F. The wet scrubbers for both processes always build up gold and silver in solution. We drain the scrubber tanks to wastewater treatment twice a week. The wastewater treatment sludge always contains both gold and silver for which we get paid for by the copper smelter, in addition to the copper.
> 
> We do run our exhaust at a pretty high velocity, around 150 cfm, knowing that we will collect gold and silver in the exhaust, but will recover a percentage of it in the wet scrubbers.


I've run many silver cells 24/7 and I've never seen them get that hot (150F). Maybe 120F max. What is the total gallonage of silver cell solution you are running? How much silver is found in the scrubber each week? The anode and cathode reaction in silver cells are never 100% efficient. Therefore, gassing can occur and solution coated bubbles could escape.

I can see how droplets from a Wohlwill cell could be picked up. These cells are run quite hot and often with air agitation.

The temperature of gold plating solutions can vary from about room temp to about 140F, depending on the type of bath. Most solutions are circulated continuously through a filter (usually a tube filter). This removes particulates and provides some agitation for the bath. If the agitation is excessive, I could see how droplets could escape in the air. If air agitation is used, this could increase the loss.

I don't think CarolineSun's questions can be answered without further information. The 1st thing I would ask is, "How did the company come to the conclusion that they were losing gold into the air?"


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## Westerngs (Apr 27, 2014)

Hi GSP,

I should have said the max, not the average, is 150F. We still do get hotter than 120F on average though, probably 130-140.
The scrubber water builds up about 150-200 ppm Ag over 2-3 days. We then drain and refill the holding tanks. Total gallons electrolyte can vary between 1500-2000. Lots of surface area by the way.


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## 4metals (Apr 27, 2014)

> Total gallons electrolyte can vary between 1500-2000.



With that much silver electrolyte you must be producing 150-200,000 oz a week. At an average electrolyte concentration of 60 grams per liter you're talking 11,000 to 14,000 oz of silver in solution. 

Assuming a 200 gallon scrubber sump, you're talking about 200 ppm or just under 5 ounces of silver in the scrubber water. 0.04% That is a reasonable carry over. 

You're not getting gold in that scrubber are you?

I have run cells on that scale and had to use a chiller to keep the electrolyte under 120 in the summer.


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## Westerngs (Apr 27, 2014)

No, that's not the scrubber we get gold in.

We have not had to use a chiller.


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## CarolineSun (May 7, 2014)

nickvc said:


> Personally I doubt the gold plating solution is releasing much if any gold into the exhaust unless they are boiling the solution. Loses from plating solutions may be in the rinse tank or the polishing shop if they finish the goods after plating, the wires used to hold the goods will also be a likely place to look or the racks used to hold the items,also possible is that the amount been plated hasn't been calculated properly. The pipes from the exhaust system should be easy to test, wipe one out and treat it, be careful and find out if it's a cyanide or acid plating solution before messing with it.
> Good luck with this and keep us up to date on your progress on solving this problem.



Thank you for your respond Nickvc! I would think they did some sort of analysis showing that the gold is losing from air exhaust. It is all confidential at this point and they wouldn't give us any more info until they hear our solution and decide to give us the job.


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## CarolineSun (May 7, 2014)

goldsilverpro said:


> May I ask what function you perform for them?
> 
> With any gassing at the anode or cathode, bubbles coated with plating solution can escape into the air, but I would doubt that this is the problem unless the gassing is severe. Why do they think the gold is being lost into the air? Analysis? How is the gold analysis being performed?
> 
> ...



We are their outside consultant if we get the job. You have very good questions, but I am afraid that I don't have any answers for them at this point. What do they use carbon filter for? To filter out the gold bath solution?

Thanks!


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## CarolineSun (May 7, 2014)

Westerngs said:


> Hi GSP,
> 
> I should have said the max, not the average, is 150F. We still do get hotter than 120F on average though, probably 130-140.
> The scrubber water builds up about 150-200 ppm Ag over 2-3 days. We then drain and refill the holding tanks. Total gallons electrolyte can vary between 1500-2000. Lots of surface area by the way.



Did you try to recover silver/gold from the wet scrubber water? If so, how? Do you use ion exchange or using some device to concentrate it and send out? Did you run any test on the air stream to see if any silver/gold lost along the ventilation system before it gets the wet scrubber?

Thanks!


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## goldsilverpro (May 7, 2014)

> We are their outside consultant if we get the job. You have very good questions, but I am afraid that I don't have any answers for them at this point. What do they use carbon filter for? To filter out the gold bath solution?


As the bath ages, it can build up organic material that can seriously affect the quality of the deposit. Some of this, especially the short-chain organics, can be removed by circulating the solution through an activated carbon cartridge for a certain period of time. Unfortunately, the carbon can also remove some of the gold.

Under normal conditions, when in use, gold baths are filtered continuously though a non-carbon string filter cartridge to remove particulate matter (dust from the air, etc.). If allowed to remain, these particles can co-deposit with the gold and create a rough deposit. Under certain conditions (e.g., if the pH is too low in acid baths, as I mentioned in an earlier post), these filters can also remove some gold.


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## Westerngs (May 7, 2014)

Carolinesun,

We do recover the metals from solution. It is done in our wastewater treatment area and is complicated due to many other metals and acids involved. We do not use ion exchange, mostly chemical precipitation.

Were I GSP, I would be reluctant to offer any more help. You state you are acting as a consultant, therefore you stand to make 
Money professionally through his advice. At this point, were I GSP, I would offer my professional services to you.


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## goldsilverpro (May 7, 2014)

Westerngs said:


> Carolinesun,
> 
> We do recover the metals from solution. It is done in our wastewater treatment area and is complicated due to many other metals and acids involved. We do not use ion exchange, mostly chemical precipitation.
> 
> ...


Thanks, Westerngs. I need you as my business adviser. I appreciate that you see the light. I have no doubt that I could solve their problems, but not until I had a helluva lot of questions answered, preferably from the plating shop owner. I'm here, Carolinesun, if you want to PM me with an offer.


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## CarolineSun (May 7, 2014)

Westerngs said:


> Carolinesun,
> 
> We do recover the metals from solution. It is done in our wastewater treatment area and is complicated due to many other metals and acids involved. We do not use ion exchange, mostly chemical precipitation.
> 
> ...



I really appreciate with your help. You are absolutely right! Thank you for taking time to answer my questions. If it comes to the point, I can make recommendations to my boss. 

Do you concentrate your wet scrubber solution? If so, how?


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## Westerngs (May 8, 2014)

No, we do not concentrate the solutions before treatment. If you need to, you can use an evaporator as I stated in your other thread.


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