Gold plating recovery

Interesting, what type of yield are you looking at here after processing?

Seems like I remember you posting about stripping some gold plated electrical items, do you play to smelt down the powder?
 
I started with 17,556.85 grams (38lb 11.4oz +/-) of cleaned and sorted pins. I was initially expecting a 0.2 - 0.3% yield (35g - 52g)

After running the first 5 lbs tonight the plating seems to be thicker than anticipated and de-plating is taking more than three times as long as I calculated. That said, it's possible the yield will be higher. If I can eek out a .6% yield that's 3.75oz at ~98% pure.

Yeah, I have a small crucible I'll run the mud through when I'm done. Test it and eBay it.

It's a good thing gold has been struggling all week. :confused:
 
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There's two ways to get the gold off the plated pins. Use acid to dissolve away all the base metals, or a stripping cell (reverse plating). The first would be cost prohibitive as nitric acid is expensive and I'd need a lot to process 38+ lbs. I also don't feel it does a very complete job. I watched a few videos of guys doing just that and they got ridiculously high yields which makes me think there was still some base metal in their yields and it took a very long time, weeks for this much material. Even if the stripping cell pulls in a little base metal it'll be easier to burn that off later in the process.

The stripping cell is pretty simple. A pyrex dish, copper basket anode, and a lead cathode.

I made my copper basket entirely out of copper, even stitching the mesh to the supports with single strands of fine copper. I've seen guys soldier the basket together but since I'm not 100% sure of the mechanics of this process I didn't want to use any tin. I know tin makes it hard to precipitate gold out of solution, don't know why but I didn't want to introduce any potential sources of tin in the form of soldier.

I made the cathode out of pure lead. It's kind of free-form with a little base to help it stand. I also added copper wires that act as a leg for stability - I didn't want it falling over and splashing acid everywhere, it also adds a place to easily connect the ground wire.

The acid is 94% sulfuric acid, bought at Lanier's in Lexington in the form of Rooto Drain Cleaner, about $20.

In the video I'm just getting started and learning as I go.

I started using the HP power supply, but it's slow. It's a 0-70VDC that can output 0-3A. I found that a car batter charger works better initially as the 10A really puts the spurs to the de-plating process. Once the outputted amps trickles down the HP does a better job of finishing it off.

It's taking a lot longer than I was lead to believe. Part of the problem is that some of the pins are hollow and plated on the inside as well. This is good and bad, it increases the surface area, which requires more amps to deplate, and thus takes longer, BUT it means more yield than originally calculated.

I was expecting a .2% to .3% yield. I started with 17556.85 grams of cleaned sorted pins.

0.2% would be 35.11 grams of gold (1.23oz)
0.3% would be 52.67 grams of gold (1.85oz)
0.4% would be 70.22 grams of gold (2.47oz)

I spent about 3 hours on Saturday and worked through about 5lbs. I've found smaller batches process faster and more cleanly. I've also found a good timing for switching the power supplies. Hopefully it'll start to go faster now. I've also noticed that just piling a bunch of pins in doesn't work so well, they really need to be in direct contact with the copper basket to work well, so smaller batches in a single layer seem to be the ticket.

I'll include detailed pics of the basket and a video of the first few runs.

Notes for the video. It's noisy, I had a fan on to keep from gagging on the sulfur fumes. The black cloud that starts to form and take over in the acid is actually particles of gold as they deplate. You'll see me put my hands on the side of the pyrex a few times, I'm checking the temp, the process is exothermic and I don't want the acid getting too hot. (eventually I went and got a thermometer).

I'll post more steps when I get to that point, and maybe more video of the process - but it's kinda boring right now - dunk pins in black sludge, watch bubbles, pull out deplated pins.

The video editor I have is clunky and counter intuitive, bear with me.

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After tonight's run its obvious I'm getting a little of the plating under the gold, nickle, maybe silver... I'll test it later for silver.

Anybody have a local source for nitric acid 66ish% ? Not thrilled about paying a $20 hazmat fee on top of the cost plus shipping.
 
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After tonight's run its obvious I'm getting a little of the plating under the gold, nickle, maybe silver... I'll test it later for silver.

Anybody have a local source for nitric acid 66ish% ? Not thrilled about paying a $20 hazmat fee on top of the cost plus shopping.
Try Carolina biological In Burlington iirc
 
0.2% would be 35.11 grams of gold (1.23oz)
0.3% would be 52.67 grams of gold (1.85oz)
0.4% would be 70.22 grams of gold (2.47oz)

Cool- I've thought of doing this in the past but never could latch onto enough plated material- those are some real chunky pins !
 
I've processed a little over 8lbs. It's so slow and my power supply failure isn't helping.

The rinse water was getting a little too acidic and had a ton of gold bearing powder in it so I brought it in, thoroughly rinsed the pins, let the powder settle. Over several hours I siphoned off the excess water letting it settle back down until I ended up with about 3/8"of powder in the bottom of a Mason jar.

To the powder I added about 300ml of HCI and about 30ml of household bleach to dissolve the gold.

I'm going to let it do its thing overnight but it looks very promising.

Remember, this is just the powder in the rinse water, the stripping cell hasn't been touched yet.

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The stannous chloride test reacted instantly and darkly indicating the very positive presence of gold in solution.

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Tomorrow I'll filter it and precipitate out the gold.

The processed pins, some of the hollow ends still have a tad bit of gold in them. I may be able to sell off the 40lb lot on ebay as scrap for a few more bucks.

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Try Carolina biological In Burlington iirc

They suspended counter service due to the virus. Had decent prices too. I bought 3l of 70% on ebay for $100.
 
Filtered...

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Added SMB...

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It's dropping! The brown mud settling at the bottom is gold....

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Side note, just running this tiny sample outdoors was a little sketchy from a fume management perspective. I'm going to have to use my sandblast cabinet with the exhaust fan on 11 for full scale production.
 
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@Alfred What metal am I contaminated with to produce the green color?
 
Do you not expect to strip some copper from your basket?
 
You keeping a running tab on costs for this, I’m curious.
 
Do you not expect to strip some copper from your basket?

I did, and I have. Already had to replace the mesh in the basket as it was getting thin and had some holes in it.

You keeping a running tab on costs for this, I’m curious.

Yes, so far I'm at about $200 and that includes the $100 I just spent on nitric acid. I suspect I'll have to buy more muriatic acid, SMB, and borax. Borax is currently sold out, as is every other thing on the laundry isles.

I've never actually done the process myself but my knee jerk reaction would be copper.

I tend to agree, yellow from the gold, plus blue from the copper would equal green. The next batch I process will get a better wash with hot HCI then HNO3 to help remove impurities prior to dissolving.

What can I say. I was excited and in a hurry
 
It's been settling for about an hour...not real happy with the dirty brown color of the remaining liquid. I suspect the future acid washes will help with that.

But there's gold in there, more than I expected out of the rinse water.

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The next batch I process will get a better wash with hot HCI then HNO3 to help remove impurities prior to dissolving.

Might want to scale the next batch down to a smaller sample so that you can "prove" your process without the "noise" of a lot of material and chemical waste. At least thats what I would do. Make it work once, then scale up once I know its possible to complete the cycle.
 
Nitric acid came in today. Cleaned up the precipitate from the rinse water with a nitric wash and aqua Regia. Ended up with 1.4 grams. The gold that makes its way into the rinse water is a fraction of what's in the cell. I've deplated 10lbs of the 38.5. I'm excited.

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This is a better photo of the nearly pure gold powder. It's really unremarkable, looks like dirt. If I can ever find borax again (wtf? Did everyone become a pepper overnight??) I'll melt it up into a shiny bead.

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Try a hardware store ? Last box I bought was to make liquid ant killer.


Me too. But since this COVID thing hit all the stores are wiped out.
 
Nitric acid came in today. Cleaned up the precipitate from the rinse water with a nitric wash and aqua Regia. Ended up with 1.4 grams. The gold that makes its way into the rinse water is a fraction of what's in the cell. I've deplated 10lbs of the 38.5. I'm excited.

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I'm confused, 10# of material got you 1.4 grams? What did I miss?
 
I'm confused, 10# of material got you 1.4 grams? What did I miss?
He pulled the 1.4g from the water he used to rinse things during the process, he needs to get working on the real stuff to figure out what the yield will be, but he’s having too much fun with the transformer and warm acid bath.
 
He pulled the 1.4g from the water he used to rinse things during the process, he needs to get working on the real stuff to figure out what the yield will be, but he’s having too much fun with the transformer and warm acid bath.

Ah... Ok. I did miss something then... I was thinking that was the yield from 10#... Didn't make sense...
 
He pulled the 1.4g from the water he used to rinse things during the process, he needs to get working on the real stuff to figure out what the yield will be, but he’s having too much fun with the transformer and warm acid bath.

It's sooooooo slow going. On a good evening after work I can de-plate about 1.5lbs over a few hours.

Boring too. If it weren't for beer....
 
Update:

All the videos I watched of guys running a sulfuric acid stripping cell, they were processing 1000g-3000g with no slowdown. I'm at roughly 4500g now and the cell is so full of powder that the powder is acting as an insulator keeping the pins away from the basket and away from the current - meaning they just sit there and I have to constantly fidget with the pins to get them to make contact and process - which slows the process even more. If the pins aren't in direct contact with the copper mesh basket they do nothing, which sucks because I can't drop in a hand full and expect it to work. It works best if I stand the pins up on end along one edge of the basket, process for a few minutes, then flip them end over end. This helps to get more gold out of the hollow ends.

I thought about just dumping everything into ice water to separate and starting with fresh acid, but I don't want to waste the acid, I don't want to have to buy more acid, I don't want to have to deal with that much excess acid, and I don't want to have to process that much extra liquid.

This morning I went out and used a 100ml syringe to suck the goo out of the cell and transferred it into a 64oz glass jar so it could settle and I could pour off the settled acid and reuse the acid, topping off the cell as needed. That's my plan anyway, we'll see how real life actually pans out.

That 64oz jar full of acid and powder is unbelievably heavy right now.

I had maybe 200ml of acid and powder left in the bottom of the pyrex dish - you can't exactly slosh around sulfuric acid to rinse the dish - so I poured it off into a beaker with about 300ml of cold water and rinsed all the powder residue out with a spray bottle. I have a new found respect for the exothermic reaction caused by adding acid to water. The beaker got hot in short order. When it's time to recover all the acid at the end of the process I'll probably have to use a bucket or two of ice to dilute everything.

The pyrex is washed, the acid is settling, we'll see how it goes.

@Alfred I did some reading on the refining process. Once I wrap up processing I'll end up with a dilute sulfuric acid solution containing the powder. That will burn off/dissolve off some impurities. Wash, rinse, and add a little HCI to make a dilute HCI wash which will burn off even more impurities. Wash, rinse, add a little HNO₃ to the slurry to create a dilute HNO₃, and heat, which should remove even more impurities. Wash, rinse, add HCI and HNO₃ to form AR, allow powder to dissolve, add a shot of sulfuric to precipitate out the lead, filter, and drop. It's a lot of work, with a lot of time between steps, but I want a final product that's close to .98% purity.
 
I’ve been thinking that to optimize the yield you might take short pieces of copper wire and twist them around the bottom structure of the basket so that you have two ends pointing up, then set the hollow pins on those. It’s a lot of time to make, setting the pins would be worse than picking up primers and I don’t know how long the wire would last.

my sense is that you’re gonna make minimum wage on this project, but that’s better than most hobbies.
 
my sense is that you’re gonna make minimum wage on this project, but that’s better than most hobbies.

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In all seriousness, I don't think you're far off.

Figure 90 minutes a pound, I'm 10lbs in, that's 15 hours so far with only 45 hours to go. Plus another 5 hours farting around with the test batch of powder and cleaning the cell. Who knows how many hours processing the powder once de-plating is done.

Let's call it 120 hours for now. I'll come back to this number when it's all said and done.
 
compounding returns though. He has the process worked out after this so the next time would be profit!
 
Not sure what I've gotten myself into here. This is a full 64oz jar of the sulfuric acid from the cell. I wanted to settle out the powder so I could re-use the acid when I start the cell back up. There is a light behind it in the first photo but it doesn't help much.

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This pic shows the demarcation line after 24 hours of settling. I realize that's not all gold, and the powder is very very fine, but damn, that's a lot of material to have to go thru. Looks like I'm going to need more sulfuric acid. I'll give it another day or two in hopes it settles a LOT more, 97% sulfuric is some thick stuff.

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Money shot.

After I drained the pan to let the acid settle I had some black sludge left on the bottom of the pan. So I rinsed it and processed it. I mixed in the 1.4g from the first batch just to reprocess it.

Got 3g total. Still, just a fraction of what's to come.

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I just tested, it's greater than 22k (91.6%). I can't test higher than 22k.

18k solution on left, 22k solution on right, my thumb nail scratch on the far right.

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Where do those pins come from?


Sent from my iPhone using Tapatalk
 
Where do those pins come from?


Sent from my iPhone using Tapatalk

Sit down.


I bought them from an acquaintance...


.... As brass scrap....


... For $40 ($1/lb).

I was looking to buy scrap brass for an unrelated project, he pulls out this bucket. Knew they were plated but "by his reckoning" there was only a few grams and not cost effective to reclaim.
 
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Everything about this is slow.

Pics of the acid settling over 2 days. I'm going to work on something else over the weekend to give it more time to settle. I have no idea what that wide "gray" band is, it is some kind of fine particles that are continuing to settle. I'd guess lead from the cathode by the color, but it's just a guess. In the third photo you can clearly see the nice crisp line of the black gold bearing material at the bottom. Expand pic.

I'm estimating 1oz ( +/- 2g) at the bottom of the jar.

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I might be tempted to extract a bit of the gray separately from the black and process it. If it’s lead wouldn’t it be cheaper and faster to get rid of it now than to let it settle and have to remove it chemically?

honestly I never thought I’d get into this process, but it’s interesting.
 
Sit down.


I bought them from an acquaintance...


.... As brass scrap....


... For $40 ($1/lb).

I was looking to buy scrap brass for an unrelated project, he pulls out this bucket. Knew they were plated but "by his reckoning" there was only a few grams and not cost effective to reclain.

giphy.gif



Sent from my iPhone using Tapatalk
 
I might be tempted to extract a bit of the gray separately from the black and process it. If it’s lead wouldn’t it be cheaper and faster to get rid of it now than to let it settle and have to remove it chemically?

honestly I never thought I’d get into this process, but it’s interesting.

Not really. Once everything is dissolved in AR - well, everything that's going to dissolve - a small shot of sulfuric into the AR will cause the lead to precipitate out, then just filter off the remaining solids (including the lead), precipitate the gold, and wash several times.
 
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