I am not sure that my gold is pure

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WillGreen

Active member
Joined
Oct 10, 2012
Messages
44
Dear All,

First I want to talk everyone who replied to my posts in the past.
You people have been an invaluable help to. I really appreciate your expertise and willingness to help. I think it's just great.

I have been reading Hokes in the meantime. Now I understand why so many of you talk about this book. It's a treasure, nothing less.

So, I have been refining some gold again and this time, I think that I did everything right.
I inquartated the gold with silver as Butcher advised me to (and not with copper), I was careful to not use too much nitric acid. In one word, everything went well.
I precipitated the gold out of the solution with copper. After drying the gold, I got exactly what I put in it up to 0.1 grams, so I was pleased with myself.
And now I am worried again ...
I melted the gold in a depression in a charcoal block (we are talking about 13 grams). The things melts and becomes a button. There is some oxidation on top of it, it's slight but it is there. The side of the button which did not come into contact with the flame (oxy-propane) has no oxidation, but the top has. I find that worrisome. Is this proof that the gold is not entirely pure? If it were pure gold, there should be no oxidation or any discoloration, or am I wrong?
Again, this may sound like a really stupid question, but I really do not know the answer.
The easy answer is to test the gold, but I do not testing equipment.
Should I assume that it is 999 or should I be skeptical?

With best regards and thank you for reading,

Will
 
For really pure gold you should do a second refining. Gold dropped out of solution with copper will not be pure. Did you at least wash the powder before melting? Don't you have a reagent to drop your gold(SMB, ferrous sulfate)? Do some reading on getting purer gold. There is plenty written about this subject. You're learning!
 
WillGreen,

I will just take a wild guess here and say the gold is still not pure, although I really do not know.

The reason I say this is because you are still new to this, I suggest you keep reading Hoke's and get a little more understanding and then re-refine your gold when your ready, if you can afford to keep this gold to get it pure and do not have to sell it at this time.

Laser Steve sells some melting dishes for around three dollars, very cheap investment for melting your pure gold.

Gold will normally need to be refined twice, and if the gold came from electronics it can be hard to get all of the impurities out of it.

Hoke’s book, and reading the posts by Harold getting your gold pure and shining (help needed section) are good steps to melting pure gold.

What color was the gold powder before you melted it was it dark like coffee or was it light brown like Caramel candy?

Does the gold have a pipe (dimple)?

Can you post a picture?

Congratulations on getting your gold.
 
Hello again,

Let me answer some questions.

I did not know what gold dropped out of solution will not be pure.
I used copper because Butcher told me a while ago to do so. I do have SMB, but I find copper easier - the first time I did this, I used way too much SMB and I didn’t know how to get rid of it again. It was a big mess.
Yes, I washed the powder before melting. I washed it in with purified water, then with hydrochloric acid, which I brought to a boil, then with water again, then again with hydrochloric acid (no boiling).
The colour of the gold was yellow - caramel candy like. I thought it looked perfect.
The gold does not have a pipe, but I have to say that I overheated it a bit on purpose.
Jewellers do that sometimes. If you melt metal which will be melted again (not worked up), you overheat it a bit to get impurities out. To me that is a sort of an automatism. If you are making an ingot, you do not overheat the metal, because it is not good.
The gold does not come from electronics. It comes from18 K jewellery. There was nothing else in it than silver and copper, aside from a bit of 18K yellow solder, of which I do not know the exact composition.
I am sorry for shocking you - it’s not that I want to be sloppy, but I am trying to be pragmatic. It is okay for me if the gold is 999 or 998 or even only 997. I can keep that in mind when alloying the gold down to 18K. We need to send our pieces to the Assay office over here - it’s forbidden to hallmark your own pieces. So, just to be completely on the safe side, my 18K gold is always 753, not 750. That is common practice over here.
Now if the gold would be 930, then we have a problem, but that is not possible, right? I thought that it would already be at least 985 after inquartating and dissolving in nitric acid.
I will try to post a picture later on.
I will check out Laser Steve’s site, thank you.

With best regards,

Will
 
WillGreen,
Now that you explained what you did in your last post, it makes me believe your gold can be purer, than I believed, in my response to your question above.

I have a bad memory, and do not remember what I may have told you in the past, I cannot keep up with what everybody is working on, I would have Only suggested cementing gold from solution if there was a problem, where using a chemical to precipitate gold either would not work or most likely not work, I do not remember the reason I told you to cement, if it was too much nitric, too much SMB, or what.

Cementing on copper is used to recover gold from solution when there is a problem , cementing a metal out of solution using an elemental metal lower in series to replace a metal in solution is a recovery method, not a refining method.

Although your gold after the steps you have done up to this point will have made your gold very close to being pure gold, it still would not be pure.

There are many atoms of metals in that gold you melted, to get every one of those atoms to be only gold, without having other atoms tag along, I think you would have had to refine your gold after the recovery of your gold cemented on copper.

Washing can help clean the gold up, but it cannot remove all of the impurity of other metal atoms, the powders you are washing are powders of gold and other metals mixed many atoms of gold mixed with atoms of other metals.

To remove all of the other metals from the gold (or as many as we can), it is normally needed to take the gold to the elemental level, removing electrons from each atom of gold, by putting the gold in solution as a dissolved gold chloride solution, then add a chemical reagent, to give back the gold atoms electrons, but not give electrons to the other base metal atoms in solution, so that mostly only gold atoms precipitate. Although when these atoms of elemental gold metal form and join together in clusters and precipitate to fall to the bottom of the beaker as gold metal powder, the gold clusters can drag down some of the other base metal atoms in solution out with them, the SMB or other reagent may also reduce a few of those base metal atoms, or some base metal atoms get locked up in the gold powders forming and get trapped in the gold cluster and drag down.

Washing the precipitate can clean up some of the base metal atoms from this gold powder, but cannot get all of them.

re-refining the gold a second time will get the gold much purer, leaving more of the base metal atoms in solution, using a different chemical reagent in the second refine to precipitate the gold than you did in the first refine, can also help to keep more of these pesky base metal atoms from following your gold, as some precipitants can also reduce some base metal atoms when you precipitate your gold, where the next chemical used in the second refine will not reduce that base metal atom as easily.
 
Okay Butcher,

You made me change my mind.
I think I did it pretty well so far, why not doing it just right?
I will refine a second time and precipitate with SMB.
I said it before, even today, but please know that I absolutely admire your competence and your willingness to help.
I find this really great. Thank you.

Will
 
Get a good melting dish, they really do not cost much, not only will your gold melt come out better, but seeing the dish after is another indication of how well you refined the gold.

Keep reading Hoke's book she explains how to get your gold more pure than I can, also using Harold's washing procedures is a great way to improve your product.

Since your gold is fairly pure no reason to in-quarter the gold and use nitric to part silver this time, if you can shot the gold it will be easier to dissolve into solution.

I would use a different melting dish to shot the gold than using to melt the final pure gold, so you do not pick up impurity from a dish used to melt dirty gold.

I am not sure if your going to dissolve the gold in Aqua regia this time or not, but if you do I would add 3.8ml HCl per gram of gold, I usually add another splash, then measure out 0.95 ml per gram of gold in another clean glass use a pipette to adding the nitric to the gold a little at a time, some hydrogen peroxide can help to keep the red fumes down, when reaction slows add some heat, when reaction stops add more drops of the nitric acid, before all of the gold is in solution concentrate the solution to see if the rest of the gold dissolves, if not add a few more drops of the nitric you measured out, after gold is dissolved continue to heat solution evaporating off any water unused HNO3, concentrate to a concentrated almost red orange solution.

Adding just a splash of HCl to see if any red fumes appear, evaporate it a little more, if done properly the nitric will be consumed by the gold and you will have no free nitric acid in solution, (and no need for the normal three evaporations to remove nitric) lower the heat and add 4 parts water, solution may turn a cloudy yellow, let it sit overnight, if silver chloride it will settle, decant solution and filter into clean jar, dip a Qtip into solution add a drop of stannous chloride to the Qtip, notice the violet color,.

Add about as much by weight of SMB to your solution that you expect gold, or what ever reagent your using to precipitate the gold, stir well and let sit (most of the gold will precipitate fairly fast but it can take overnight for every bit of the very fine powder to settle as the solution gases SO2, if solution color is clearing again use a Qtip and stannous to test for gold in solution (this can be done before all of the gold has settled), after gold is out of solution the color of the remaining liquid is also an indicator how much base metals were involved, this gold powder can then be washed using Harold's washing procedures.
 
Most of us who deal with small amounts of gold cannot afford to have a whole lot of gold tied up in the electrolyte solution of the cell to get pure gold using the Wohlwill Process, although I would like to try it someday, to get that purity of gold the beginning anodes and electrolyte would need to fairly pure to begin with.
 
Dear Butcher,

Thank you for your input.
I am following your advice. I did it before and it helped me tremendously. This said - and this is not practical - I’m not sure I understand your explanation, but then I am not a chemist. Isn’t it true that if I would take one electron of any atom of your body and compare it to any other electron in the universe, it would be exactly the same electron? An electron is just an electron. I do not understand what is going on in an Aqua regia solution - the gold dissolves, the end product is auric chloride (one atom of gold for every four chloride atoms, I believe). The nitrogen stays in the solution, or escapes as NOX, the hydrogen escapes too. But there is no stripping of the atoms of their electrons or am I wrong? If this would happen, wouldn’t be elements just disappear?
I am sorry for my ignorance, but I do not understand this.

Thank you for enlightening me - I read up on Harold’s ways of washing. This too is going to help tremendously.

All the best,

Will
 
Will,

The bar of metal contains many atoms, your gold bar has many millions atoms of gold, with lets say several millions atoms of copper mixed in the metallic crystal structure, to separate the copper atoms from the gold atoms we dissolve the metal into solution.

Gold or the copper atom has electrons in orbital shells, the electrons orbiting the nucleolus of protons and neutrons, making up the atom of gold, these orbiting electrons can be pulled away from the atom of copper or gold, by a halogen like chlorine gas, chlorine in its elemental state is missing electrons and wants an electron to fill its shell, it will steal an electron from gold or copper.

In our solution we will use an oxidizer like a halogen chlorine the oxidizer (missing electrons in their atoms) this chlorine gas atom will take the electron from an atom of gold, the chlorine now gaining the electron to fill its shell will be reduced the chlorine to chloride (reduced means to gain an electron), now the gold atom missing an electron becomes oxidized (oxidized means missing electrons), this oxidized gold is now in solution as a dissolved salt of gold, with the chloride bond in solution as gold chloride AuCl3, a water soluble salt of gold, (metal + acid = metal salt of that acid).

Two moles of Gold metal (Au), with three moles of chlorine gas (Cl2), make two moles of Gold chloride salt (AuCl3).
2 Au + 3Cl2 --> 2 AuCl3

Now to get our gold back out of solution we need to give the Oxidized (missing electron) Gold back the missing electron, to Reduce (gain of electron) the Gold back to a metal to precipitate it out of solution as metal gold powder billions of gold atoms with all of the electrons given back to each atom.

For something to be reduced something else must be oxidized (it is a movement of electrons from one atom to another, so to reduce gold back to metal we can use a chemical to precipitate gold, the chemical is oxidized in the reaction to reduce our gold.

The trick in refining is to give back the gold atoms electrons, without giving back the copper atoms their missing electrons, thus reducing the gold from solution but not reducing the copper atoms from solution.


Now lets look at getting the copper out of solution. The oxidized copper (missing electrons) dissolved in solution, if we put an elemental metal lower in the reactivity series in the copper chloride solution, like a bar of iron, which the irons atoms in the bar has all of its electrons, but is more reactive than copper, in the acid the (oxidized) copper will take away electrons from the iron atoms, now the copper with a full shell of electrons is (reduced) to copper metal and forms copper metal powders on the bottom of the container, The iron now losing electrons is Oxidized and dissolves into solution as iron chloride.

We could use another metal higher in the reactivity series of metals to replace iron from solution, like zinc, here we would get back iron powders and have a zinc chloride salt in solution.
 
butcher said:
We could use another metal higher in the reactivity series of metals to replace iron from solution, like zinc, here we would get back iron powders and have a zinc chloride salt in solution.
Click to expand...

I remember reading, on a thread I can't exactly recall, essentially the same process for processing the stock pot. I didn't ask then, but understanding more, my question is, can we skip copper and just use iron? Carrying it further, could we skip the iron too?
 
Say we have gold and copper and iron dissolved in solution.

If I add a copper bar of metal, I would cement out gold, leaving copper and iron in solution.

But if I added a bar of iron, I would cement out gold and copper, leaving iron in solution.

Or if I used aluminum I would cement out gold, copper, and iron from solution, leaving aluminum in solution, and because aluminum is above hydrogen in the reactivity series, I would remove hydrogen gas from my acid.

Google several articles on reactivity series of metals and study this till it makes sense.
 
Hello now I understand
So if I used a reagent (smb) on any
Metal salt it would precipitate the elemental
Metal out
Does a reagent have an affinity to any salt
more or less than another?
Excellent post!!!
These are answers that I never new the question to
But needed to finally understand
Thanks Steyr223. Rob
 
Rob, i dont believe SO2 will precipitate any other elemental metal except gold. thats why we use SMB to precipitate gold. it will precipitate other metals, but in the form of sulfates. these sulfates can be removed with hot water rinses.
 
Although SO2 (SMB or other sulfite) is more specific for gold, and will precipitate gold before copper, SO2 will precipitate copper from solutions, it can also precipitate some palladium, so here we see using SMB, our gold could contain some copper or palladium.

Ferrous sulfate will precipitate gold but it can also precipitate some platinum.

Notice how these two reagents can precipitate other metals with our gold.

Many of these reducing agents we use to precipitate gold are not always specific for gold, they can precipitate traces of other metals, although if solution is free of base metals as much as possible we can expect fairly clean gold from precipitate with minor metal contamination, and solutions holding the other metals, because these reagent can precipitate traces of other metals, this is why it is normally suggested to use a different reagent for the second refine, the other reagent will not normally precipitate out the same metals as the first reagent used will.

So here we can see, if we refine twice, using different reagent with each refine we can get a better quality gold.

We remove the majority of base metals (nitric acid to dissolve base metals, copper, silver, palladium) before dissolving gold, most of the other insoluble metals (PGM)are separated here in our recovery methods, or when dissolving gold, some traces of metals are removed during the process (after denoxing and dilution silver chloride and lead sulfate), and each step in recovery and refining removes traces of these other metals from our gold, re-refining can remove what was not removed in the first refine, using a different reagent in these refines to give us more pure gold, the more times you refined the gold the more you could remove, but also it becomes harder to get the traces of impurities to separate, and loses of gold traces may outweigh the benefit, I have read where to get almost pure gold they would refine eight times or more, and still not remove all of the atoms of other metals, these atoms are small and with millions of them it is hard to chase all of them away from your gold.

Study Hoke's she speaks of this, and explains it much better.
 

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