Foil removal/collection cell

[aga]

... gold dissolved in solder will be almost colloidal.

I was about to ask how you'd know if you had a colloidal solution, then remembered the laser trick.

Just shine a laser pointer through the liquid.

If you can see the beam, there are particles in there.
If you can't see the beam, there are only dissolved atoms in there.


The Left hand tube contains some of vinegar/salt liquid which clearly has some particles in it that are not dissolved. Doesn't mean it's gold, just that there are particles of some kind.

The one on the right only has distilled water in it : no beam=no particles.

I think the theory goes that for something to scatter the laser beam, it has to be at least as big as the wavelength of the laser, or something like that.

This is a 532nm laser pointer, and a gold atom is 144pm in diameter = 0.144nm, so if this was a colloidal gold solution, the gold atom-clumps would be made up of at least around 3,700 atoms, probably less accounting for the space between them.

Just need 32,061,894,054,054,100,000,000 of those to make a 1 gramme ingot :lol:

 

[anachronism]

I like that trick. Thanks Aga.

Jon

 

[aga]

I forgot to mention that a laser pointer can blind you !

NEVER EVER look directly into the beam : always shine it straight down into the tube/cup and look at it from the side, at a distance.

 

[anachronism]

I forgot to mention that a laser pointer can blind you !

NEVER EVER look directly into the beam : always shine it straight down into the tube/cup and look at it from the side, at a distance.

Ok ok ok - yes we get the message don't go from one extreme to the other mate lol

(haha that was funny)

 

[Topher_osAUrus]

Hah.

Thats a nice little trick aga, I knew it would work for determining tubidity of an AR solution with AgCl, but had no idea it was applicable for colloidal gold.

Thank you

 

[chuckgambale]

I often hear of the dangers of the acids that we work with and I think that at least most of us know those inherent dangers. I had my own drain cleaning business for some time and many of the acids and other chemicals are perfectly safe to dispose of. I also grew up in a small town in Massachusetts with a very big sewage treatment plant. Now both of this already said and please listen, it is the metals in solution that cause the biological issues for the marine life in sewage treatment plants. It is the metals in solution that cause all kinds of medical maladies from leaching into groundwater wells. If you use vinegar and salt to put copper in solution and you dump it down the drain because there is no dangerous acids you need to study way more. Maybe we should talk more about the dangers of metals in solution more or at least as much as the acid dangers.

 

[chuckgambale]

This is in no way reflected on the op I just hear how safe this vinegar leech is and cringe. Sorry if it felt like an attack

 

[anachronism]

This is in no way reflected on the op I just hear how safe this vinegar leech is and cringe. Sorry if it felt like an attack

Stating your opinion in a reasoned way is never an attack Chuck. You've every right to state your opinion sir. Too many snowflakes out there these days who don't like to hear a contrary viewpoint though! Don't apologise.

Jon

 

[aga]

Sorry to be going from one extreme to the other.

Still finding my feet in this forum, and am more than happy to take any guidance anyone has to offer.

People stating what is on their mind is not offensive to anyone with a brain behind their ears, so please do not be concerned.

Yes, heavy metals ARE lethal to many organisms, especially in an oxidised state, noteably aquatic life in the case of copper, so the vinegar/salt solution is NOT 100% safe in the sense that it can be put down the drain.

I only meant that it is safer to work with, but got the sense mixed up/unclear, which is why i edited those posts to remove the '100% safe' parts.

Quite often a new reader only reads the first few posts in a thread, so leaving the misleading information seemed wrong.

Appologies if that has made this thread make less sense and i will not do that again (i.e. not post stupid and flippant comments like that).

I will devote some time to rendering the resulting liquid neutral and safe to dispose of, or better, re-use, then post the results here.

The temptation to go ahead and try to refine the miniscule amount of gold foils i have stripped so far grows each time i look at them in the collecting pot, so that series of experiments may happen quite soon.

 

[aga]

Fuming nitric isnt necessary in any refining really, so you can save that for something else :twisted:

Converting the 56% agricultural grade nitric acid i have (which is tinted orange/brown, probably iron) to Pure nitric acid, i'd react the acid with something cheap, extract the crystals, dry them, then distill over conc sulphuric acid to get 99.9% pure nitric acid, then dilute that down to whatever is required.

Quite a lot of work really, plus lots of dangerous hot acids and NOx fumes.

Does it really matter if you have totally Pure acid in the refining process ?

 

[Topher_osAUrus]

Fuming nitric isnt necessary in any refining really, so you can save that for something else :twisted:

Converting the 56% agricultural grade nitric acid i have (which is tinted orange/brown, probably iron) to Pure nitric acid, i'd react the acid with something cheap, extract the crystals, dry them, then distill over conc sulphuric acid to get 99.9% pure nitric acid, then dilute that down to whatever is required.

Quite a lot of work really, plus lots of dangerous hot acids and NOx fumes.

Does it really matter if you have totally Pure acid in the refining process ?

It may not be iron, but just NO2 gas, like the difference between red and white fuming nitric.

I think it would be fine for refining purposes to be honest, but there may be a contrary viewpoint another member may shed light on.

 

[anachronism]

If the sheet that comes with the 56% Nitric says it's 56% Nitric and doesn't mention contaminants then that's what it is. You should have that sheet with the delivery.

The red/brown tinge that you mentioned is probably what Topher mentioned above. Was it delivered in an opaque container? If you think that's iron then you might want to do some further reading on Nitric acid and it's derivatives and by products.

I wouldn't waste your time trying to distil it or make fuming Nitric. Not only does it serve no purpose but it's also horrendously dangerous in that form. Why do it?

 

[FrugalRefiner]

Converting the 56% agricultural grade nitric acid i have (which is tinted orange/brown, probably iron) to Pure nitric acid, i'd react the acid with something cheap, extract the crystals, dry them, then distill over conc sulphuric acid to get 99.9% pure nitric acid, then dilute that down to whatever is required.

Quite a lot of work really, plus lots of dangerous hot acids and NOx fumes.

Does it really matter if you have totally Pure acid in the refining process ?

No.

The orange/brown color may or may not be iron. When nitric is exposed to light, it can begin to break down into other NO_x compounds, which we see as the BFRC.

When you dissolve your gold it is rarely pure (otherwise, you probably wouldn't be dissolving it). We use selective reducing agents to precipitate the gold and leave the impurities in solution. A bit of iron shouldn't cause you a problem unless you're trying to produce ultra pure gold, like 4N+.

Dave

 

[g_axelsson]

You are hooked now... :mrgreen:

Nice trick with the laser.

The reason I said "almost colloidal" was that the powder had a distinct purple tone and went straight through my filter paper but it settled finally. The purple color disappeared when I put it into AR.
Colloidal gold made from testing with stannous have a purple color and true colloidal gold solutions usually goes in red and purple depending on size of the particles.

To check for contaminants in nitric acid, just add some to an evaporating dish and let it evaporate. Anything left is what was dissolved in the nitric as contaminant.
Unless you are trying to make 99.999% pure gold a bit of iron or other contaminant in the nitric doesn't affect it much.
If you have palladium in the nitric (that would be a pleasant problem) it might contaminate the gold if you are using SMB (SO₂) as precipitant, but then there are a couple of other precipitants to select from, iron sulfate, oxalic acid or ascorbic acid for example.

Göran

 

[aga]

This nitric acid was just 9 euros for about 5 gallons, plus 2 euros deposit on the container.

No paperwork comes with it as it is intended for farming use.
The brown is most likely Iron as this is probably a by-product of some other industrial process.
That can be tested here, so i will do so tomorrow and post the results.

Purifying it does carry a lot of Very Serious, potentially Lethal dangers, especially in the distillation step, so it is good to hear that might not be necessary, even though i'd make a max of about 100ml.

As a noob to gold refining, i assumed that the purer the reagents were, the purer the end result would be.
Probably another wrong assumption as ways must have been worked out over the years.

Having said that, without chemically pure reagents, how does one assay the end product's purity ?
Weight/density surely will not be enough to calculate down to 0.1%, or will it ?

I understand that there are some X-ray diffraction techniques, but i just do not have that kind of equipment.

 

[Topher_osAUrus]

I know the crystallization in the pipe on melted gold can give some guru's here a great idea on the golds purity (and even some impurities, i.e. Pd gives a fern crystallization pattern on the gold itself...copper makes the gold more orangish reddish, silver more green)

The colour of the precipitated powder can also give a bit of a clue, light tan is a good sign its high purity.
Color of the washing liquors is another indication.

Color of the borax after melting is one more.

But, as far as testing impurities at the home hobby level...
...um.. Got a buddy with an xrf? -far from *exact* but, can give a general idea.
Atomic absorption is another one, but, also outside the hobbyists level

I know there is more, but I cant recall at the moment.

 

[g_axelsson]

A good scale and fire assay can go quite far up in purity but at some limit it is hard to find out how much mass is missing. Then you can use spectroscopic methods and calculate the fineness by difference.

Here is a discussion that talks about a couple methods.
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=41&t=24292&p=257445#p257445

For the amateur some visual cues goes far. No oxidation on the surface when melting a button, crystallization of the molten gold with a nice pipe and mirror like surface is all signs on good purity.

To get good purity you should wash the gold after it is precipitated to get rid of some contamination before melting. Don't forget cleaning your torch and use a clean melting dish.

Here are links to both Harolds and Lou's tips on cleaning the gold.
http://goldrefiningwiki.com/mediawiki/index.php/Washing_gold_powder

Check this post for a picture of Harold's breakfast bowl. :mrgreen:
http://goldrefiningforum.com/phpBB3/viewtopic.php?p=3248#p3248

Göran

 

[aga]

Thanks for tips and links. So much to learn here !

As promised, the nitric was tested for Iron ions (Fe³⁺) and came out positive.
Not a huge amount present, but definitely there.


That was with diluted acid and a few drops of ammonium thiocyante solution.
If enough Iron ions were present, it would go intensely red, like blood.

P.S. very much enjoying Hoke's wonderful and practical book !

 

[Topher_osAUrus]

P.S. very much enjoying Hoke's wonderful and practical book !

She did write a couple books that were spectacular.

And that little amount of iron i dont think would cause you problems in your refining gold to standard purity.
Maybe if you try Lous crazy 6N purity method youd need nuch better acid...and water.

 

[g_axelsson]

P.S. very much enjoying Hoke's wonderful and practical book !

She wrote more than one book, links to downloading "Testing Precious Metals" is at the bottom of
http://goldrefiningwiki.com/mediawiki/index.php/Hoke

Göran