Gold refining

[goldsilverpro]

Thanks for the clarity Chris.

Nick alluded to a point that I wanted to expand upon. If you have a situation where you've processed lots of processors in AR and you have 12 litres of solution that's loaded with in excess of 13g of gold per litre, and all the associated base metals including silver:

Would you still create an additional 36 litres of waste to get the silver out on the first pass or would you filter and drop immediately. Then redissolve in a much smaller volume say under a litre and subsequently triple the volume of this much smaller amount in order to get clear of silver?

Nick, Pat, and I have done it on the basis of using the first (larger volume) dissolve as recovery, and the second (small volume) dissolve as refine on many occasions and find it to generate much much less waste overall.

I understand that if it's initially small quantities of gold and liquid then it doesn't make much of a difference but I'd appreciate your thoughts.

Jon

In that case, I wouldn't dilute the 1st drop 3 to 1. I always like some dilution to make the gold drop go smoother, especially with all those dissolved base metals, and would probably do a 1 to 1 dilution for the first drop. Then I would redissolve the Au and do a 3 to 1 for the 2nd Au drop. Every deal is different.

For karat gold, I don't inquart unless I have green gold or maybe some left over solids from a previous batch. I just dissolve in very hot AR and then use a 3 to 1 dilution. This dilution reduces the effects of too much nitric, to a limit, and also eliminates most all of the effect on Au purity from all those dissolved base metals. I rarely need a 2nd refining and I never need to get rid of excess nitric with karat golds. I did have a method of cleaning up slightly off-purity gold in the melt by using a few pinches of niter, borax, and soda ash. That almost always worked. To me, though, the main secret of good salable purity is in the dilution and crystal-clear filtering.

If the Karat gold items aren't bulky, I don't even shot them. When the dissolving gets too slow, I use one of several methods to get rid of the AgCl crust. I'm a play-it-by-ear refiner, especially with karat gold, and I've always said that I have never done karat gold the same way twice. That's an exaggeration but not much of one. However, I've never worked in a refinery where karat golds were the main item. If I did, I would develop the ideal method, like 4metals does, and get the right equipment to handle it. Except for the film refinery I worked in, all the rest were job-shop refineries, i.e., they took in anything that would make money, even scrap base metals occasionally. Most of them, including the 2 I had, always had a batch of karat gold cooking away in the back corner of the hood. My little karat gold batches usually held only 5-10 oz of gold.

 

[g_axelsson]

When I do CPU:s in AR I use too little AR to run it to completion in the first time. When the reaction dies down I test the liquid and if it is barren (often is) I pour off the waste into a settling beaker, cover the CPU:s with AR again and continue dissolving metal.
If I time it right I can remove most of the base metals before the final run when I put the gold into solution. This gives me a concentrated solution with a high gold content and not too much base metals. The gold usually drops very nicely.

Any gold dissolved in the beginning cements back onto the exposed metal. First run is always with a smaller amount of nitric, just enough to pierce the plating so the acid gets full access to the base metal underneath. By having a lot of HCl in the first run it's the perfect way to expose the kovar pins and then dissolve them in HCl without wasting a lot of nitric acid.

My method (which I first read about here on the forum) suits me well but it takes longer time, especially since I don't use heating. The solution sits in a safe place outside and I check on it daily.

Just as Chris I'm judging what to do based on what happens while I'm refining. Every batch is different... or at least behaves differently.

If Dave is a frugal refiner, I am a slow refiner. :lol:

Göran

 

[FrugalRefiner]

If Dave is a frugal refiner, I am a slow refiner. :lol:

Sounds like a frugal approach to me! 8)

Dave

 

[anachronism]

If Dave is a frugal refiner, I am a slow refiner. :lol:

Sounds like a frugal approach to me! 8)

Dave

If I even UTTER the word frugal to my other half, her eyes turn to chips of stone... Then again she works darned hard for her money so let her enjoy it. 8)

 

[goldsilverpro]

When I do CPU:s in AR I use too little AR to run it to completion in the first time. When the reaction dies down I test the liquid and if it is barren (often is) I pour off the waste into a settling beaker, cover the CPU:s with AR again and continue dissolving metal.
If I time it right I can remove most of the base metals before the final run when I put the gold into solution. This gives me a concentrated solution with a high gold content and not too much base metals. The gold usually drops very nicely.

Any gold dissolved in the beginning cements back onto the exposed metal. First run is always with a smaller amount of nitric, just enough to pierce the plating so the acid gets full access to the base metal underneath. By having a lot of HCl in the first run it's the perfect way to expose the kovar pins and then dissolve them in HCl without wasting a lot of nitric acid.

My method (which I first read about here on the forum) suits me well but it takes longer time, especially since I don't use heating. The solution sits in a safe place outside and I check on it daily.

Just as Chris I'm judging what to do based on what happens while I'm refining. Every batch is different... or at least behaves differently.

If Dave is a frugal refiner, I am a slow refiner. :lol:

Göran

I think I was the one to originally post the method, about 9 or 10 years ago. The first time I saw that done was nearly 40 years ago. The guy had a steam heated 50 gallon Pfaudler kettle about 1/2 filled with stainless and inconel parts that were gold brazed. A lot of the extraneous non-gold-bearing base metal had been sheared off before dissolving. He dissolved the base metals with AR (he added the HCl and HNO3, separately, as needed - a gallon of AR will dissolve about 2 pounds of most common base metals) to the point where the AA showed dissolved gold. At that point, I doubt if there was more than 1-2% of the base metals left undissolved. He then cut the heat and added some additional base metals to cement the dissolved gold until the AA showed no gold. At that point, everything was stopped. After settling, siphoning, and filtering, the solids were transferred to beakers and dissolved in AR. The gold was then dropped, as normal. Very impressive. Since then, I've used the process for various types of High base metal material. Works great.

As an experiment, several times I have split a lot of material just to see if the 2 halves reacted the same throughout the process They never did. There was always something that necessitated doing something different to one of the halves.

 

[anachronism]

It's funny how these things come about isn't it? I do something similar 8) I must admit I hadn't wanted to bring it up before now in case I was actually doing something dumb.

 

[goldsilverpro]

It's funny how these things come about isn't it? I do something similar 8) I must admit I hadn't wanted to bring it up before now in case I was actually doing something dumb.

As long as a process is safe, efficient, fast, simple, cheap, low labor, and fun, basically in that order, nothing you can ever do is dumb. I would say that safe and efficient are nearly tied for first. By efficient, I mean that you're getting all of the values or, at least all but that last little bit which is too expensive to worry about.

 

[deandadnaed]

Ok guys. I’m a newbe. So please be patient with me.

The first times I did this:

Adjust pH to 12 using NaOH in solution (when I do this the adjustment always produced Ammonia).
I use 2g of Zinc powder (.325 mesh) for every 1g of Gold that I know is in the solution. I know 2NaAu(CN)2+ Zn > Na2Zn(CN)4 + 2Au. I add the Zn while stirring.

I let the solution settle over night.

Then I filter the solution. The liquid contains cyanide so I add either H2O2 or Sodium Hypochlorite to oxidate CN. The solids are dried and transfered to a beaker. I cover them with water and I use HNO3 (under a fume hood). Gas evolves and I continue adding HNO3 until no reaction is observed.

I filter the solids, neutralize the liquid with Sodium Carbonate. The solids are washed and heated in dilute HNO3. When no more reaction is observed. I filter again, neutralize the liquid. And the solids are a dark brown powder.

But my actual yield is very low.

Can anybody give me some advise?

I cannot denox the main solution because it contains Cyanide, so adding Sulphuric Acid or Hydrochloric Acid is out of the question.
I cannot use FeSO4 because it does not precipitate gold in alcaline solutions.
I wonder if NOx are preventing to precipitate all gold in the solution, but I’ve tried adding Zinc in excess to “force” the equilibrium and precipitate gold but it hasn’t improved and naturally I use more HNO3 to leach it and leads to more NO2 formation which is very nasty.

I wonder also if Ammonia has any relation to the low yield. And how can I get rid of the Ammonia (that by itself is very unpleasant to work with).

Please, help. I’m stucked with this problem. I’m willing to do this right and to learn from those who are more experienced.

Any help will be appreciated. Thank you in advance.

 

[anachronism]

If you are trying to get the gold out, I would question why you are adding an oxidant to the solution as part of the process. What purpose does it serve?

 

[deandadnaed]

Hi!

I don’t get it.

If you’re talking about Peroxide/Hypochlorite. I add it to destroy the remaining CN once I’ve filtered the (Zn+Au).
If you mean HNO3, I use it to dissolve the Zn, and let the Au stay.

But I’m still learning. I’m open to ideas/advises.

Thanks for reading me!

 

[deandadnaed]

When I do the addition of Zinc. I let the solution stay and settle.

I decantate:

To the liquid (which I believe has some CN) I treat it with Peroxide or Hypoclhorite.
The solid is dried and transfered to a beaker and I add HNO3 to leach out the Zn (though it has some ZnCN). So I’m aware I still got a lot to learn, but that’s why I’m trying to get advise in order to: make things safely, and improve the quality and yield of my work.

 

[nickvc]

How do you know your yield is low, do you know how much is in the solution and if so how?
You may find that to recover the gold you will need an excess of zinc dust, also heating the solution helps but add the zinc slowly to avoid a boil over, adding a little caustic to the solution I also find helps. The other alternative you have is to plate the gold out of the solution which will avoid a lot of the nasty fumes and dangers of mixing cyanide and acids, you will not recover all the gold but if done correctly most of it leaving what’s left for zincing.

 

[deandadnaed]

How do you know your yield is low, do you know how much is in the solution and if so how?
You may find that to recover the gold you will need an excess of zinc dust, also heating the solution helps but add the zinc slowly to avoid a boil over, adding a little caustic to the solution I also find helps. The other alternative you have is to plate the gold out of the solution which will avoid a lot of the nasty fumes and dangers of mixing cyanide and acids, you will not recover all the gold but if done correctly most of it leaving what’s left for zincing.

Thank you very much for your advise! I really appreciate it.
I indeed know how much gold is diluted in AR. So I know how much is in solution. These are my first attempts in recovery. Perhaps I’ll get better when I practice until I master the technique.

Still I wonder if someone has attempted to work in such a system. Hoke’s right, best way to go is by FeSO4, or SMB. But my problem is, I don’t have Au from AR only, in that case it’s a little more straight the methods with less hazard involved. But I’m bounded by cyanide to high pH values.

I was wondering, if I destroy Cyanide with the Au in it (by Peroxide or Hypochlorite) can I destroy NaAu(CN)2? In that case does anyone think I’d be left with AuCl3 (for the Hypochlorite, for Peroxide I’d be adding some HCl once the Cyanide is gone) and then proceed via Hoke’s (denox, copperas or smb and so on)?

So basically I can’t follow Hoke’s because in spite of being gold dissolved in AR it contains also Ammonia and Cyanide.
I follow something like Merril-Crowe (Gold cementation by Zinc additions) I’ve read the method posted in this forum by goldsilverpro, and yes, it works. I just don’t know if that methods is the best when Ammonia, Citric Acid, and presumably an excess of NItric in AR. Because it’s not Sodium Gold Cyanide salt that has been dissolved in water, but Gold attacked in AR (forming AuCl3) which is later added Ammonia, Citric Acid and the cyanidated (by adding NaCN). I know Sodium Gold Cyanide is the same either prepared from metal or from salt. But my solution contains also Ammonia, Citric Acid, and I consider an excess of Nitric (just to be sure).

:shock:

 

[anachronism]

I don’t get it.

If you’re talking about Peroxide/Hypochlorite. I add it to destroy the remaining CN once I’ve filtered the (Zn+Au).
If you mean HNO3, I use it to dissolve the Zn, and let the Au stay.

Peroxide is most commonly used as an oxidant for the CN whilst Hyopchlorite can be used to destroy CN. If you're adding peroxide you can re-dissolve your gold and make your solution active again which will cause problems dropping the remaining gold.

 

[deandadnaed]

I don’t get it.

If you’re talking about Peroxide/Hypochlorite. I add it to destroy the remaining CN once I’ve filtered the (Zn+Au).
If you mean HNO3, I use it to dissolve the Zn, and let the Au stay.

Peroxide is most commonly used as an oxidant for the CN whilst Hyopchlorite can be used to destroy CN. If you're adding peroxide you can re-dissolve your gold and make your solution active again which will cause problems dropping the remaining gold.

You’re absolutely right!
By adding and oxidizing agent I’m at risk to oxidate Au itself affecting the reduction to metal state. I’m not sure when the equivalent point of CN with H2O2 is, so I always add an excess just to be sure. But that is done to the liquor that I obtain after the Zn addition. At this point I don’t expect the liquor to have but small amounts of Gold. The solids I’ve filtered is where the Gold metal, and Zinc metal (that has neither been used in displacement nor in the hydroxide formation ZnOH because it’s done at pH=12) should be.

If I understand correctly that grey powder which contains Au and Zn both in metal states, that I can treat with HNO3 to leach out the Zn. Au being in metal state should neither be redissolved nor attacked.

But again, that’s textbook chemistry. I know that in actual life things often run differently.

Thank you very much for your counsel.

 

[anachronism]

It's my pleasure. 8)

Jon

 

[deandadnaed]

Well.

As newbe I’ve got another cuestion.
I’ve melted my button. Although the metal has some Borax crust all over the surface. I assume I’ve did a poor job when glazing my crucible.

Any suggestions on how to get rid of the Borax crust?

Also. Can anybody tell me some tips to improve glazing my crucible in order not to end when I melt my metal with a borax crust?

 

[kernels]

There are a few ways to remove the borax, you can heat the gold button up to red hot again and drop it in some cold water. You can also just put the whole button in a flask and boil it in water for a while, the borax will flake off / dissolve.

 

[deandadnaed]

There are a few ways to remove the borax, you can heat the gold button up to red hot again and drop it in some cold water. You can also just put the whole button in a flask and boil it in water for a while, the borax will flake off / dissolve.

Thank you! I really appreciate all the support I’ve been given. This is my first attempt and you must know all the mixed emotions one can bear when you achieve something for the first time.
I thank you all.


Enviado desde mi iPhone utilizando Tapatalk

 

[anachronism]

You can also put the button in dilute sulphuric acid and warm it. Leave it there and you will see the borax disappear.