# Gold Surprise



## Dog Biscuit (Sep 3, 2007)

I am currently processing a 4-pound batch of contacts from several large burn-in boards. Gold was recovered using HCl/P. Due to the shape of these contacts, and the fact the HCl/P did not disolve the base metals, I was forced to do much rinsing and filtering.

When the HCl/P process was completed, I burned the filters and soaked the residue in diluted nitric acid. After filtering, the nitric acid was placed into a bucket for neutralizing. The ash residue was processed with the HCl/Ch method.

When I turned to neutralizing the nitric acid (aprox. 24 hours later), I noticed what appeared to be small gold flakes floating on the surface of the acid and a reddish-brown precipitate and the bottom of the bucket. I filtered the acid again and used HCl/Ch to disolve a sample to the precipitate. A test with stannous chloride showed a strong gold content.

Question: Where did the gold come from?


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## Platdigger (Sep 3, 2007)

Did you dilute the nitric? Like say with tap water?
Randy


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## Dog Biscuit (Sep 3, 2007)

The nitric was diluted 3-1 w/ tap water prior to running the filter ash through it.


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## Platdigger (Sep 3, 2007)

Well, if there is any chlorine in your tap water it can form a dilute aqua regia and desolve some of your gold.
Randy


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## lazersteve (Sep 3, 2007)

The gold may have been absorbed by the AP in the orignal reaction. It may have partially precipitated by the dissolved base metals and was then caught in the filter. The nitric removed any base metals and left the gold. Stray chlorine in the water may have dissolved a very small amount of gold, but not very much.

Steve


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## Dog Biscuit (Sep 4, 2007)

Thanks for the thoughts. I am wondering if there was some AP residue left in the filter ash. Any HCl left could have combined with the nitric acid to make a weak AR. In any event, I ended up with aout 1.5 grams of gold powder in the nitric acid waste. I'm glad I looked before tossing it.


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## Platdigger (Sep 4, 2007)

So you smelted the reddish-brown precipitate?
Was this were you got most of the gram and a half?
Also, if I may, what did you use to neutarlize the nitric with?


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## Harold_V (Sep 4, 2007)

Platdigger said:


> Well, if there is any chlorine in your tap water it can form a dilute aqua regia and desolve some of your gold.
> Randy



Not in the presence of base metals. Even if gold was to dissolve, it would immediately precipitate on base metals that are present. 

The worry about chlorine in tap water is *way* over stated. Rarely is it a problem----it (tap water) can be used routinely with no worries---aside from working with silver nitrate. Even then, if a trace of silver chloride isn't a concern, it works fine for that purpose, too. 

Harold


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## Platdigger (Sep 4, 2007)

I see, must have been the hcl residue then? Like Biscuit figures, yes?
I still would like to know what he used to neuturalize the nitric with and if he was able to smelt the precips.....


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## Harold_V (Sep 4, 2007)

Regardless of the types of acids present, as long as you have base metals that have not dissolved, you won't lose gold by dissolution, the exception being if you can separate the solution from the metals quickly, before precipitation can occur. This feature can be used to great advantage when you must dissolve undesirable things to get to the gold. By starting with less than the amount of acid needed, things are dissolved until the acid is exhausted, then if the solution is allowed to sit with the base metals, values will precipitate, eliminating even more of the base metals, which go into solution as the values are exchanged. When a the solution tests barren, it can then be decanted and the process started over. While I don't recommend this procedure under normal circumstances, it is one of the tricks you can employ when conditions don't lend themselves to separating base metals from values by other means. 

It's important to note that the gold, or other values, may not be recognizable--having been dissolved and precipitated. They likely will look like nothing more than mud in the beaker. 

A note, perhaps of interest. We do not *smelt* our metals, the *melt* them. Smelting is the process of reducing metals from ores. The two processes should not be confused. 

Harold


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## Dog Biscuit (Sep 4, 2007)

Platdigger, After I filtered out the powder, I neutralized the nitic acid with carbonate of soda. The powder was then re-dissolved in HCl/Chlorox, dropped with sodium sulfite, and is awaiting the torch.


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## Platdigger (Sep 4, 2007)

Sorry Biscuit, I should have studied your original post better. But, you say you never noticed this powder until 24 hours later. So, this was before you neuteralized the acid? I have a reason for all these questions, hope you don't mind.....


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## Dog Biscuit (Sep 4, 2007)

No need to be sorry. Asking questions is how we all learn. Yes, it was approximately 24 hours after I filtered the ash. Nothing had been added to the nitric acid and it showed a very pale green color when I noticed the gold. After removing the gold powder I added a piece of sheet steel resulting in a very minor coating of copper.


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## Platdigger (Sep 4, 2007)

Interesting, so what you are saying is the gold fell out of the nitric acid solution, with the only base metals being present being those that were already in solution.
So Harlod, is this common?
Randy


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## Harold_V (Sep 4, 2007)

I'm at a loss to explain what happened------but gold can and will self precipitate under the proper conditions. It's very eager to return to the elemental state-----occasionally doing so violently, depending on the compound involved. 

I would comment that it isn't common for a metal that has been dissolved along with gold to precipitate any gold if all of it has been dissolved. While I don't understand the chemistry involved, it's a matter of the state of the element involved. There must be an electron exchanged in order for one element to precipitate another. The state of the precipitant dictates whether it will work, or not. For instance, ferrous sulfate that has turned brown no longer has the ability to precipitate gold-----apparently because it has lost the needed electron. If I'm wrong, I welcome a correction. 

In this case in question, I would consider that the solution has oxidized---reacting with the atmosphere, perhaps? Dunno!

Harold


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## Platdigger (Sep 4, 2007)

Yea, It's kind of like when I added sodium metabisulphate and got what looked like no reaction, only to find the gold powder down the next day. Like maybe conditions were right for the gold to drop right away......you just can't see anything for awile.........
Or oxidation from the atmosphere as stated.
I am still interseted in how soo much gold got into nitric.
Of course, I have read were you Harold have metioned that any hcl residue on the gold could cause some to disolve when you hit it with the nitric....or at least I believe that is what you wrote.
Randy


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## Platdigger (Sep 4, 2007)

Exuse me, thats metabisulfite....."ite".....


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## scavenger (Sep 4, 2007)

A while ago when I was just learning I did a small batch of header pins in strong nitric. After the violent reaction there appeared to be nothing left. I figured my gold had either gone up with the fumes or had been dissolved in the nitric. I neutralized it with urea and tried SMB. No luck. Being a learner I didn't know to use iron to drop everything so I got rid of it. I understand that nitric alone will not dissolve gold so the only explanation I can think of is that the gold plate was disintegrated into very fine particles by the violent reaction. After reading this thread I am certain that if I had let the solution sit for a day or two my gold would have dropped to bottom.


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## Harold_V (Sep 4, 2007)

Platdigger said:


> I am still interseted in how soo much gold got into nitric.
> Of course, I have read were you Harold have metioned that any hcl residue on the gold could cause some to disolve when you hit it with the nitric....or at least I believe that is what you wrote.
> Randy



Yes, I've stated that on a few occasions, including one where the discussing became quite enthusiastic when GSP suggested washing the precipitated gold powder with nitric. Sure, it works, but you risk dissolution of some of it in the process because gold is precipitated from a chloride solution, and it's difficult to render it harmless. 

On many occasions I'd pre-treat materials with both nitric and HCL. I always incinerated between the two processes, otherwise values were always dissolved when moving from one acid to the other, regardless of how well I had rinsed. There are times when a pretreatment by both acids will yield a solution of values that is very clean, and dead easy to filter----and almost impossible if not so treated. 

Harold


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## Platdigger (Sep 5, 2007)

Man! It's good having you here Harold......
Such a wealth of experience.


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## Harold_V (Sep 5, 2007)

Thanks, but I have nothing more than that which any of you can acquire by being diligent ------and studying Hoke. 

One thing that is to advantage to anyone that is willing to listen to my advice: I have no agenda-----aside from sharing the things I learned, often the hard way. I no longer refine, and have no desire to do so. My proudest moments are when I can help bail out someone that is impatient and does stupid things (I mean that kindly), and think all is lost. 

So far, it's been a lot of fun for me to, hopefully, be helpful. When it becomes burdensome, I'll quit!

Harold


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## Dog Biscuit (Sep 9, 2007)

How the gold got into the nitric acid is still a mystery, but I'm pleased to show you the result. This little 5.9 gram beauty came, via the "scenic route," from 4 pounds of contacts.  

http://i186.photobucket.com/albums/x73/Ooopsiemybad/Burn-inbd5.9gram003.jpg

Lesson learned: Always check solutions before disposal.


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## Noxx (Sep 9, 2007)

Wow, your gold nugget looks very pure and very shiny. We also see a nice pipe in the middle.

Good job !


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