Final refining gold, - brainstorming

[solar_plasma]

I am slowly moving towards learning the final refining of my gold and in flood of information I get a little bit lost. It is confusing, there are just so many possibilities, which all have pro's and con's.

For the first, ofcourse I don't get more money for many 9's, but I feel it like a kind of apprenticeship certification exam in one field of the subject of gold refining.

My material comes from everything gold containing stuff around me, it is medium brown and will surely still contain all possible contaminants, - proper incinneration, washing and precipitation is easy read but needs time to be learned. I'm not sure, if I also will blend it with gold powder from broken jewelry (inquartation) or dental gold (straight AR if possible).

It is only a first brainstorming for me. It would be a pleasure, if anyone likes to comment or advise.

After all I read I tend to following course:

Removing any basemetals left:

repeated hot full strength lab grade HCl, wash intensively (remove basemetals and Pd)
dissolving in HCl/chlorox (or better AR? I would prefere chlorox)
properly driving off excess chlorine by heating
dillution, filter off AgCl (if any), H2SO4, filtering off PbSO4 (if any)

Now the gold stays in one only beaker, which is used for the rest of the procedure:

precipitation with potassium metabisulfite by avoiding excess (test)
potassium may precipitate Pt (if any) as a complex, but Pt will be left in solution under the oxalic precipitation


Removing PGMs:
wash
redissolving in AR / minimum amount HNO3 / sulfamic acid solution [1] EDIT: better without sulfamic and doing it the old style
precipitation with oxalic acid (http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=61&t=10827)
decanting/washing

repeated hot full strength lab grade HCl, wash intensively, not filtering but decanting (closely following Harold's description)

test all left over liquids for PMs

melt gold without any flux in clean porcelain crucible, which was prepared with a little melted borax
cast button
EDIT: a pipe and a shiny surface without oxidation or crystallizing are indications for high purity


[1]
Lou:

Yes, if you add the solid to a beaker or flask which is heated not by steam but by a hot plate or mantle, you risk the decompositon of the sulfamic acid into an ammonium cation, which causes precipitation of ammonium salts of the PGMs. All of those salts re-dissolve (some faster than others) in aggressive AR, but with significant NOx production vis-a-vis oxidation of ammonium ion.

Solution, dissolve the most sulfamic you can in boiling hot water, and slowly add that hot solution in until N2O ebullition ceases. Obviously, the vessel you do this in must be setup to collect acid mists or you will have values lost in entrainment from the bubbling/off-gassing.

 

[butcher]

Oxalic acid would not be used for a first refining.

Actually you can get a very pure gold with SMB and or ferrous sulfate, Oxalic acid would be more trouble in my opinion, and using SMB (or FeSO4) you could get fairly pure gold, refining it the second time will give a very pure gold, using a different precipitant the second refining will actually help to give you a more pure product, and when using Harold's gold wash technique of the powders, you can also clean up the gold powders of some of the contaminate that made past the refining stage.

The main thing is elimination of base metals before you dissolve your gold, the more pure the gold is put into solution the more pure it will precipitate back out of solution.

As far as incineration, if you have carbonous trash, or tin or other trouble some ingredients then it is needed to help eliminate the trouble makers, after incineration a boiling wash in HCl will help to dissolve these troublemakers from your gold powders, Harold has given great advise on the details.

I would not normally mix the gold with jewelry, I would recover and refine these two feed stocks separately.

I do not know if this helps any with the confusion.

 

[solar_plasma]

Oxalic acid would not be used for a first refining.

I believed those above are two refinings, since I dissolve and precipitate twice. But this is only one refining?

Actually you can get a very pure gold with SMB and or ferrous sulfate, Oxalic acid would be more trouble in my opinion, and using SMB (or FeSO4) you could get fairly pure gold, refining it the second time will give a very pure gold, using a different precipitant the second refining will actually help to give you a more pure product, and when using Harold's gold wash technique of the powders, you can also clean up the gold powders of some of the contaminate that made past the refining stage.

Therefore I made one step metabisulfite (maybe I should even use SO2 to avoid any unnecessary source ofpossible contamination?) and the next oxalic, since it is said to not to pricipitate Pt, if the solution is properly denoxed. I am mostly concerned about PGM contaminates, because I have dissolved and precipitated parts of the powder several times, anyway I got some very fine black after brown powder. I am not sure if this is just finely devided gold, basemetals which I also would expect to be dropped at last or if it is PGM contaminate (though I never had any positive on PGM with stannous after dropping gold). I have to reread focussing on that.

The main thing is elimination of base metals before you dissolve your gold, the more pure the gold is put into solution the more pure it will precipitate back out of solution.

So, I will make the HCl washings before and after and at last most properly, so much for sure.

As far as incineration, if you have carbonous trash, or tin or other trouble some ingredients then it is needed to help eliminate the trouble makers, after incineration a boiling wash in HCl will help to dissolve these troublemakers from your gold powders, Harold has given great advise on the details.

As I said, the powder is brown and has been dissolved, washed and pricipitated before, - just not as properly as it could have been done. Maybe I should incinerate again, just to be sure? - Okay, when I ask this, I have given the answer by myself! :shock: :lol: "...when will people learn to incinerate?...." :lol:

I would not normally mix the gold with jewelry, I would recover and refine these two feed stocks separately.

Thank you for the advice. That makes the decision easy.

I do not know if this helps any with the confusion.

Ofcourse it helps. Only reflecting on other's thoughts I can validate and verify if I have understood what I believe I have understood!

A last question: Do I have any chance to get 99,99 purity by the procedure above or where could I optimize to get the last 0.01's? Maybe adding a step with DMG to eliminate PGMs?

edit: maybe I should repeat 10 times in every washing step.... in radiation protection we consider 10 half-lives with a decay to a stable element to set the radiation to zero, maybe this could be transferred to leaching processes too....on the other side, if I repeat 5 times in the first washing, 3 times in the next and 3 in the last, I have 11 at all, should be enough.

Also I will use only new vessels and avoid any contaminations from dust in the air. Maybe I should buy some clay cruicibles first instead of enamaled porcelaine, which I have? Or best quartz...

 

[solar_plasma]

I think I will go back to the basics, not re-invent the wheel, but try to get the best result by a typical refining - it's more valuable to get routinely "only" industry standard by proven cost effective methods, than to waste lots of time and oceans of chemicals and water to achieve artifically a higher purity.

So: incineration, washing, chlorox, metabisulfite will be the way, - just doing it perfectly now

Thank you very much for reflection!

 

[solar_plasma]

Just for the record, here's the 5,5 g material, I talked about (from 7 g recovered stuff (additional 0,5 g settled later and 0,3 g of my old bad 2,3g button was left undissolved, so I've removed 0,7 g basemetals). Clearly visible the thin dark layer which pricipitated at last.

 

[butcher]

Unless you are working with material fairly high in the platinum group, you most likely would not have much if any of them after the first refining of your gold. most of the platinum group are actually hard to get to dissolve into solution in the first place, and what does go into solution will normally pretty much stay in solution when you precipitate the gold, base metals are much more likely to contaminate the precipitated gold.


The black powder is more likely due to copper in the precipitated gold, which when fairly pure will be a lighter brown color, other base metal salts like lead or silver chloride can also be involved, washing per Harold instruction will help to remove some of the contaminates, lead chloride (boiling hot water washes), copper chloride in the hot HCl washes (along with other base metals that make soluble chloride salts), and the ammonium hydroxide wash will help to pick up silver chloride, a final wash in dilute HCl to remove the ammonium complex is helpful, the water washes between each of these washes helps to remove traces of metals and salts that the acid (and base) made more soluble. as the gold gets cleaner and lighter brown in color it will settle faster, dirty gold seems to not to settle as well as clean gold does, the washes will improve the gold in purity but can only do so much.

when you dissolve the gold for a second refining you dissolve the remaining base metals, each time you refine the gold you leave some of the base metals in solution when you precipitate the gold, in precipitating the gold the second time the solution and gold will be cleaner (less base metals than the first refining, this will also precipitate a more pure gold (with less drag down of base metals than the first refining, your remaining solution is also much cleaner as it holds less base metal than the first refining solution held after the gold from it was precipitate.

Most of the chemical precipitants we use are very selective for gold, although with over use some of them will precipitate some base metals for example SMB is selective for gold and will precipitate a really pure gold product, but if solution is loaded with base metals like copper the gold is more likely to drag copper down with it, and if we overuse the SMB we can reduce some of the copper from the solution with our gold, (there is less chance of doing this in the second refining due to the lower copper or base metal content in solution.

Also doing the second refining with a different precipitant which will not reduce the same base metal is also helpful, an example would be doing the first refining and precipitate the gold with copperas (this would be my choice if PGM's were involved), and refining the gold a second time precipitating it with SMB, this way the second chemical will not reduce the same contaminate the first one might reduce.

Solar I think you are on the right track, but I think you may be over-thinking it a little bit.

 

[solar_plasma]

Thank you so much, Butcher!

 

[Geo]

i agree with butcher. Harold has taught that you can achieve high purity gold with SMB and proper washing. unless you really desire ultra pure gold, which is hard to achieve outside a well equipped refinery, you may just be adding more steps and more work to your process.

 

[FrugalRefiner]

dillution, filter off AgCl (if any), H2SO4, filtering off PbSO4 (if any)

I tried to post this yesterday, but I guess my connection flaked out on me. Rather than dilute and filter, then add the sulfuric and filter again, You can save a step by diluting and adding the sulfuric at the same time, then filtering a single time. You can separate the lead sulphate from the silver chloride with hot water washes. When you dilute, use cold water or ice to precipitate the maximum amount of AgCl.

Dave

 

[steyr223]

Butcher said " solar you might be overthinking a bit" :lol:

Hey solar I will bet you never been told that before. :shock:

Steyr223 rob

 

[solar_plasma]

@Richard

Solar I think you are on the right track, but I think you may be over-thinking it a little bit.

Indeed.

@Geo

i agree with butcher. Harold has taught that you can achieve high purity gold with SMB and proper washing. unless you really desire ultra pure gold, which is hard to achieve outside a well equipped refinery, you may just be adding more steps and more work to your process.

But I am very curious how much purity I can achieve by a standard refining. Purity and yield are two measurable parameters, at which I can prove what I have learned or not have learned. It's like to beat my own high score.

@Dave

I tried to post this yesterday, but I guess my connection flaked out on me. Rather than dilute and filter, then add the sulfuric and filter again, You can save a step by diluting and adding the sulfuric at the same time, then filtering a single time. You can separate the lead sulphate from the silver chloride with hot water washes. When you dilute, use cold water or ice to precipitate the maximum amount of AgCl.

That makes sense! Thank you!

@Rob

Butcher said " solar you might be overthinking a bit" :lol:

Hey solar I will bet you never been told that before. :shock:

I've been told that sometimes by my hazmat captains. :lol:

Thank you all!

Björn

 

[Anonymous]

If you have access to Sulphuric acid you can also take out a lot of copper using the sulphur/peroxide method.

It's not one that's commonly described but it's a great way for getting the remains of the copper out of your powder and it's a completely controllable reaction, even though of course concentrated sulphuric acid is an extreme hazard.

Jon

 

[solar_plasma]

Yes, I thought some seconds of dilluted sulfuric and I have experiences with dilluted piranha. Even dilluted it is extremely dangerous and no one who reads this should think of using it full strength - leave it to professionals who know its dangers and proper use! (unless he is a professional).

Controlable? Surely not to everyone!

Please be careful when posting extremely dangerous processes!

 

[Anonymous]

I think you're wrong to tell me off for mentioning a process that is actually valid. It's not some half baked lunatic idea, it's based upon valid and accurate chemical process.

I mentioned that it's not commonly described- and then I didn't describe it. I think your post is a little over the top Solar. If you knew the process details you would know that one of the benefits is exactly that it's completely controllable.

Don't get all emotional at the mention of Sulphuric acid mate.

Jon

*(edited for grammar)

 

[solar_plasma]

I am not emotional with any acids like conc. sulfuric I use dailly at work. I am emotional about HF and CN-'ses, because I do not know them in practice, - and don't want to. :lol:

 

[Geo]

that IS one of the solutions that has been described on the forum and was quickly shot down by more than one moderator. i believe what solar_plasma said was a valid point and that it should never be advised. there are too many new members that do not understand the dangers and are willing to try anything they read here without first researching it. when you advise a dangerous process or even mention one, it should at least be followed by a warning letting viewers know how dangerous it is and that it should not be used except for trained lab technicians.

 

[FrugalRefiner]

Please be careful when posting extremely dangerous processes!

I think you're wrong to tell me off for mentioning a process that is actually valid. It's not some half baked lunatic idea, it's based upon valid and accurate chemical process.

I mentioned that it's not commonly described- and then I didn't describe it. I think your post is a little over the top Solar. If you knew the process details you would know that one of the benefits is exactly that it's completely controllable.

Don't get all emotional at the mention of Sulphuric acid mate.

Jon

Jon,

I don't see solar-plasma's response as telling you off. He provided a warning for others who may read this thread and asked you to be careful when mentioning it. I also don't see that he got emotional at the mention of sulfuric acid. Sulfuric by itself is dangerous. Sulfuric with peroxide raises the hazard level.

I'm going to go along with solar-plasma and Geo on this one. Piranha is a valid process, as are HF treatment, cyanide, and others. But they are also very dangerous. All of the processes we use are dangerous, but these are even more so. When we post, we have to keep in mind that many people read this forum who may not have the background to understand the elevated risk. If someone devotes the time to studying the forum, they'll come across descriptions of all of these and more, but they'll be learning of the hazards along the way.

Dave

 

[Anonymous]

Ok fellas, taking the reasoned approach to this.

If the forum membership are using the safety procedures that are well documented, i.e. Goggles, gauntlets, ventilation masks, correct ventilation in the building and proper equipment then I'm struggling to see how using Sulphuric acid presents more of a hazard in terms of personal safety.

I know and completely accept gentlemen that it's in many ways more harmful and less forgiving than HCl, and please believe me when I say that I'm not looking to create a squabble about it. That being said, if what you are saying is that the membership is not capable of understanding these points then I'll refrain from suggesting anything like this in future.

I was, however under the impression that there were quite a few members who had progressed beyond refining in their kitchen using Pyrex jugs, and I apologise profusely for suggesting something that requires more of a clinical approach.

Please accept my apologies, I will not make the same mistake again.

 

[solar_plasma]

Sulfuric is not piranha. The combination of sulfuric and H2O2 reacts more violent than everthing else I ever saw and I only saw a very dilluted version of it. Standard safety is not enough, when a not trained person handles full strength piranha.....even a hazmat suit level A/type 1 will probably only provide temporarily limited protection when a beaker of piranha explodes in front of you.

Personally I feel that comparing piranha with conc. sulfuric is like to compare conc. HCl with dish soap. BTW piranha is NOT sulfuric but peroxymonosulfuric acid.

http://en.wikipedia.org/wiki/Piranha_solution
http://en.wikipedia.org/wiki/Caro's_acid

 

[Anonymous]

I think maybe we're talking about different things gentlemen . The method I use is not violent, quite the opposite. It was shown to me by a professional gold refiner with over 35 years experience. It's also incredibly effective.

The method I'm describing is not linked to either of the links above.