Cleaning precipitated gold powder

[Anonymous]

Thanks but the old saying "if its not broke,don't fix it"works for me.
I have no problems with the way I process.If that works for him,and it must or else he wouldn't do it, then that is great.This is about Hcl dissolving/not dissolving gold,not superoxygenated Hcl.

 

[Oz]

Mic,

You are absolutely correct, if what you are doing works for you there is no reason to change it.

Now let me explain why I said what I did. As you have pointed out, most anyone you talk to, or any respected book or reference on refining says that HCl alone will not digest gold. Because of this many people when washing gold in HCl will toss the solution as having no value without testing first. They are tossing out gold sometimes when they do so. Not every time perhaps depending on their procedures, but often enough.

I do much of my gold digestions with HCl and Cl2 gas (chlorine gas), as such there is no nitric to be carried over in the process. If I precipitate this gold with SMB from a dirty solution and need .9995 gold I will decant and wash it in hot water. After decanting again I add HCl and put the beaker on a hot stir plate with a stir bar included. I set the temperature to about the same as a hot cup of coffee and set the stirrer to high. The stirring action chops significant air into solution (the air we breath is roughly 21% oxygen by volume). This gives enough oxidation potential to the solution to digest finely divided gold in a reasonable time frame. I then re-precipitate my gold.

Now it is fair of you to say that since I do this intentionally it has no bearing on the subject at hand. Let me give you this to consider. Platinum is far more difficult to digest in HCl and the oxidizer of your choice than gold is. Cold temperatures also slow down chemical reactions. One winter I had cemented some Pt from a chloride solution with zinc. I decanted it and washed in HCl to remove any excess zinc, then decanted again and added some water and a little HCl to prevent freezing since I was setting this aside until I had more Pt to add to it (it was only about a quarter of an ounce). This Pt ended up setting for 2 months in weak hydrochloric acid with only exposure to the air with no agitation or stirring. In that 2 months enough of the finely divided Pt had gone into solution to significantly color it. I decanted this and cemented enough Pt out of the solution for it to be worth the trouble.

I am not out to sell what it is I do to others, it works well for me. Neither am I just some armchair refiner, I have more than a slight clue as to what I do and see when I refine. You will find that when I post direction on the forum I speak from my own experience with repeatable results, if not of my own experience I say so. I am not a fan of unfounded idle speculation. Nor am not out to rewrite Hoke or anything else that has been written by others. I am here to say however that the books are not always right or do not always tell the whole story.

Would you wish I only tell people what is in the books, or is it more beneficial for me to tell them what is not in the books? Some of the most valuable things I have learned on this forum came from experienced members that were teaching something from their own experience that is not found in the books. I believe in giving back.

If you still doubt me, follow my procedure and then come back and tell me if I am wrong.

My intent here is only to educate members that they should test their wash solutions before discarding them. They work hard for their gold, I would like to see them keep all of it. It would be a shame to discourage such a simple precaution as a stannous test.

 

[Harold_V]

plain HCl can digest gold. As part of my gold refining routine I take my once refined gold powder (after washing) and place it on a hot stir plate in HCl to re-digest it for precipitating a second time.

In 6 years I have never once seen common muriatic acid digest refined gold,whether its boiling or not.
Do we need to rewrite Hoke and the forum handbook?

No, no need to rewrite Hoke. I am of the opinion that HCl is NOT dissolving gold. I've had a similar experience, which I found not to be dissolution at all.

I experienced gold chloride when washing gold on rare occasion. Finally isolated the problem as drag down, where I had precipitated a large volume of gold (this occurred when I re-refined) which had trapped some of the gold chloride---to be exposed when I started washing.

Solution?
Piece of cake. I learned to stir the precipitated gold well, and to add a little more ice if the solution was hot (often very hot), which immediately precipitated the residual gold. Note that I had SO2 running through the entire operation.

I can honestly say that in all my years of refining, I never, once, knowingly, had a problem with HCl dissolving gold.

Harold

 

[Harold_V]

I read advices to boil precipitated gold powder in hydrochloric, nitric, sulfuric acid, wash with ammonia and use more substances. What do you think about boiling precipitated gold powder boiling in HCl, where several drops of nitric are added (such a very weak AR)?

What do I think?
I think you need to lose that idea and pay attention to what has been proven to work reliably. Part of that is losing the notion that gold, after precipitation, should be washed with nitric in any way. It's not necessary, and can be the source of one hell of a lot of frustration. You can achieve gold above industry standard (9995) by simply washing properly, and using good, clean handling practice.

There's no way in hell you should be washing gold with AR---regardless of how dilute it may be. What's the point?

Harold

 

[Renaldas]

it's hard to tell by the picture, but trust me, this is purple, and the powder washed well with platy of water.

Then you still had residual nitrates on your powder.This is why harold preaches to incinerate.You can wash it with boiling water a thousand times and still have residual nitrates.

Maybe there are not nitrates, but air oxygen? I also have positive test for gold after boiling in HCl. As you know, combination of oxygen and HCl act as a weak AR.

 

[samuel-a]

Oz

I couldn't have said it better... use your own experience, and test acid washes as well, that's it, sometimes it's positive, sometime it isn't...
I didn't spoke about the "why gold may be present in HCL wash" , only the "if it is there, then..."

the main point again, test with stannous...

Good luck to all

 

[Lou]

Gold will certainly dissolve in hydrochloric acid that is open to air. It will not be quick at high temperatures, but in a cold agitated solution, I can promise you that some gold will dissolve. This would only be significant if it were really cold out and the vessel were open with stirring. We have members here using compressed air and HCl to dissolve gold.

Leave HCl open to air, when it starts to yellow then that is chlorine gas being produced that is dissolving in the acid. HCl is not an oxidizing acid, but the chloride counterion itself can easily be oxidized to elemental chlorine by oxygen in the air (which becomes water), just as Oz said.

 

[dtectr]

Do we need to rewrite Hoke and the forum handbook?

maybe... 8)

Edit:

here is the stannous test of the HCL washes from my last inquaration :


it's hard to tell by the picture, but trust me, this is purple, and the powder washed well with platy of water.

IMHO, I think we're apples & orange-ing here ...
Sam is not dissolving & then precipitating gold - he is inquarting, if his terminology is correct.
Inquartation seems to be ALMOST a mechanical process (i know its chemical, officially; but follow me here)-
The silver & base metals ARE dissolved, but gold is not, & is therefore NOT precipitated, as it never goes into solution to begin with; it merely remains behind as an INSOLUBLE. If the remaining gold particles are small enough, they would TEST as
gold in solution, when in reality, they are really just really tiny insoluble PARTICULATES, not PRECIPITATES.

I think we're ALL accurate (obscure "Absence of Malice" [Columbia Pictures, 1993] reference),

Again, if terminology is correct ...

if I'm missing something, let me know ...
just my dos centavos

 

[Harold_V]

Gold will certainly dissolve in hydrochloric acid that is open to air. It will not be quick at high temperatures, but in a cold agitated solution, I can promise you that some gold will dissolve. This would only be significant if it were really cold out and the vessel were open with stirring. We have members here using compressed air and HCl to dissolve gold.

Leave HCl open to air, when it starts to yellow then that is chlorine gas being produced that is dissolving in the acid. HCl is not an oxidizing acid, but the chloride counterion itself can easily be oxidized to elemental chlorine by oxygen in the air (which becomes water), just as Oz said.

Interesting comment. I trust that the fact that I never worked with cold chemicals was the chief reason I had no problems? I would expect that the heated solution drove out any free oxygen, thus I had no problems.

Harold

 

[Anonymous]

This would only be significant if it were really cold out and the vessel were open with stirring.

This may be why I have never experienced this.I've never used a stir bar,most of my soultions are heated ona hotplate,and even if they are not........I live in florida,we do not know the meaning of "really cold".

 

[Lou]

Chlorine is well soluble in cold water. Once upon a time I worked on water sterilization--you'd be surprised how much chlorine will go into cold water.

Funny thing is that the rate of dissolution will be less with the cold, but the solubility of the chlorine is higher.

You know it is the truth because HCl will gradually go from clear to yellow with oxygen absorption (which results in a reaction). Metals like iron promote this.

Lou

 

[patnor1011]

Now I am starting to be worried.
I left fingers in AP outside for about 5 weeks now. Last time when I checked a week ago they were stripped clean but I did not had time to remove them
We had very cold weather last few weeks sometimes up to -15`C so now my foils may be dissolved. Ill check that tomorrow.

 

[Barren Realms 007]

You should be ok.

 

[adam_mizer]

Newbie here, reading this thread thought I would add in some of my small experience.

I have or had 25-30LB's of good high grade boards mix a little low most hygrade or thicker foil plate.
Removed the components with a heat gun.
Soaked these boards in HCl crock pot method. Earlier on I tested some small boards in a coffee pot and HCl to see reaction of old solder.
Some of the boards must have flash plate because when I pulled the samples out I saw the discoloration from Gold to nickel, I guess nickel under the flash plate.
The sample was done in approx 45 degree. (Lowes Muriatic 31.45%) HCl removed some flash plate.

The other day I ran several pounds of boards in the crock pot with lid and set on low/warm outside maybe 35 degree's. It did better as the flash plate withstood better this time but it still was noticable ever so slightly.
Most of the boards have heavy plate so I could not tell if any gold went into solution from them. But the gold does go into solution because the flash plated missing gold. Not much but it does!

So from reading I'm concluding that it appears that the small amount of oxygen striking the surface of the HCl bath does get into the solution but in my case only very slightly not bothering me (yet).
Somehow I don't think thats what I'm looking for.
But Harold say's the HCl won't pull the gold out and it is contamination of some sort then the circuit board with the lead, so the lead/tin is the contamination, (other than copper/nickel/gold/traces).
It was nice to see solder lead was cleaned off very good to the surface (now very flat). After stashing the HCL away for another use I saved the bottom debree also for another day.

These boards are then run in AP. Added air-pump to the AP bucket after waiting many days of slow production. Wow now I'm cleaning out foils almost everyday. Solution is working great.
When I find out the solution won't work anymore then I'll test for gold in solution. Meanwhile I'm getting out all I can get. A few pounds of boards and also 1/2-1lb fingers at the same time constantly.
Boards put on their side standing up so to speak and air bubble flow between them with fingers spilled between them also.

Funny that some of my foils are in tiny tiny pieces but I'm not complaining just learning to deal with it since its a hobby.

 

[qst42know]

Harold.

Did you use tech grade HCL from a drum or hardware store muriatic from a thin plastic bottle?

I wonder if that would be part of the difference?

 

[Harold_V]

Harold.

Did you use tech grade HCL from a drum or hardware store muriatic from a thin plastic bottle?

I wonder if that would be part of the difference?

For general processing and washing I used tech grade, purchased in 55 gallon drums. However, when washing my re-refined gold, I used reagent grade. I used to buy it in 5 gallon lots. I understand the chance of re-dissolving gold, but I have to say, it simply was not an issue for me, even washing with tap water, which was my routine. I attribute that, chiefly, to the fact that I did everything at high temps---never cold. I expect that traces of gasses were evaporated quickly, thus avoiding any problems. And yes----I did test with stannous regularly. I learned, early on, how valuable testing is.

I am of the opinion that if washing gold is producing gold chloride, there's something more at play than gasses that are being absorbed from the atmosphere.. such as contaminated HCl.

I might also note that I was never stupid enough to mix acids----I was faithful to incinerate if I had need to go from HCl to nitric-----and never, ever, washed with nitric. In spite of what you may hear, you can rinse precipitated gold time and again and still not remove all HCl, so washing with nitric will always present risk of dissolution. It is expelled upon extended heating-- when drying, or by melting.

Harold

 

[Palladium]

Gold will certainly dissolve in hydrochloric acid that is open to air. It will not be quick at high temperatures, but in a cold agitated solution, I can promise you that some gold will dissolve. This would only be significant if it were really cold out and the vessel were open with stirring. We have members here using compressed air and HCl to dissolve gold.

Leave HCl open to air, when it starts to yellow then that is chlorine gas being produced that is dissolving in the acid. HCl is not an oxidizing acid, but the chloride counterion itself can easily be oxidized to elemental chlorine by oxygen in the air (which becomes water), just as Oz said.

I've mentioned several times that i have been processing pins in my 15 gallons plastic barrel setup using ap and compressed air. I have a 5 micron polypropylene filter bag fiberglass resin glued to the hose that i use for bubbles. I process outside under a building that is open and temp right now is around 40-50 deg F. I've talked about the gold that will go into solution because the amount of air that i am putting into the system. There is only about 5 gallons of solution in the barrel and when i hit it with the air it increases the volume of the liquid 2 fold. Once i have filtered the ap solution the gold that is there is so small from being agitated that it is hard to filter and deal with. I have noticed that once the ap solution is filtered for any undissolved gold that i am still recovering gold ( dissolved ) from the spent ap solution in the next step. So yes gold does dissolve in hcl but it is a function tied to the amount of oxygen present and will increase exponentially as such. I love the cold for my processing. It just seems to work better for me than heat with my setup. 8)

 

[Anarchy618]

I have been adding small amounts of powder together untill I had a decent amount. When I tried to clean it with hcl to remove impurites before melting (due to dark discoloration of powder mixed with impurities ) what would make the solution turn so violently blackish & appear oily?

 

[g_axelsson]

You should really invest in some proper beakers, it is so much easier to pour from to avoid spilling our precious gold. And using a beer glass is sending the wrong signals to your brain, it only takes a split second of confusion to make a mistake.

Göran

 

[Shark]

To add just a bit more to Goran's advice. Those narrow bottom glasses make a nice visual when precipitating your gold, but they sure are easy to tip over when filled to the brim (I know they are weighted on the bottom, but accidents do happen). I have used all kinds of glassware and still use some, but my selection is shrinking constantly because of the faults I have found from actual usage. At a minimum use a decent glass coffee pot, and then, only if you restrain the amount of heat applied to it. Buy a beaker or three and be glad you did. They will take heat better than the average coffee pot by a large amount, and they have premeasured marks that help a lot. They also come in sets that really keep the costs down. I wish I had bought them sooner than I did.