# Final refining gold, - brainstorming



## solar_plasma (Oct 18, 2013)

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.

Click to expand...

_


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## butcher (Oct 18, 2013)

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.


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## solar_plasma (Oct 19, 2013)

> 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...


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## solar_plasma (Oct 19, 2013)

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!


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## solar_plasma (Oct 19, 2013)

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.


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## butcher (Oct 19, 2013)

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.


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## solar_plasma (Oct 19, 2013)

Thank you so much, Butcher!


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## Geo (Oct 19, 2013)

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.


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## FrugalRefiner (Oct 19, 2013)

solar_plasma said:


> 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


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## steyr223 (Oct 19, 2013)

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

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

Steyr223 rob


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## solar_plasma (Oct 19, 2013)

@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


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## Anonymous (Oct 19, 2013)

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


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## solar_plasma (Oct 19, 2013)

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!


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## Anonymous (Oct 20, 2013)

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)


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## solar_plasma (Oct 20, 2013)

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:


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## Geo (Oct 20, 2013)

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.


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## FrugalRefiner (Oct 20, 2013)

solar-plasma said:


> Please be careful when posting extremely dangerous processes!





spaceships said:


> 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.
> 
> ...


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


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## Anonymous (Oct 20, 2013)

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.


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## solar_plasma (Oct 20, 2013)

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


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## Anonymous (Oct 20, 2013)

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.


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## solar_plasma (Oct 20, 2013)

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

*Disclaimer:
This method is not adviced in this forum, because of its hazards. There are threads, where it has been discussed. *


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## Anonymous (Oct 20, 2013)

Yes Sir- my method is neither of the methods described in your links.

Maybe we have a language issue here that isn't helping as it's possibly causing some misunderstanding Solar.


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## solar_plasma (Oct 20, 2013)

> Maybe we have a language issue here that isn't helping as it's possibly causing some misunderstanding Solar.



Maybe. I talk chemistry. Maybe you didn't mean conc. sulfuric acid and you didn't mean H2O2, I don't know. But that is, what you described.


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## Anonymous (Oct 20, 2013)

I'm not going to lower myself to squabble with you on a public forum Sir.

You don't know enough about what I mentioned to make a proper judgement call. You heard Sulphuric acid and Hydrogen peroxide and made a whole host of assumptions. 

Let's leave it at that and move on.


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## solar_plasma (Oct 20, 2013)

> 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



That's what I heard. Cónc. sulfuric and peroxide, where I assumed you meaned hydrogen peroxide, which was mentioned later and I don't believe, that you have contradicted that. Those two are something quite dangerous and even if only unpropper mixed tend to explode while heating to 120°C, not to mention, what will happen, if they are used uncorrectly. Controllable? Yes, a controlled demolition is also controllable, but not by everyone who reads this thread.


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## martyn111 (Oct 20, 2013)

solar_plasma said:


> > Those two are something quite dangerous and even if only unpropper mixed tend to explode while heating to 120°C




Having carried out this process with Spaceships, and having read his posts above, heating of this process to 120c has never been mentioned, nor is heating part of the process.
The very process is exothermic, providing all the heat that the reaction requires, the hydrogen peroxide is used to oxidise any copper in the gold powders and then with the addition of the sulphuric acid the copper oxide, produced by the previous reaction, is dissolved.


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## FrugalRefiner (Oct 20, 2013)

martyn111 said:


> Having carried out this process with Spaceships, and having read his posts above, heating of this process to 120c has never been mentioned, nor is heating part of the process.
> The very process is exothermic, providing all the heat that the reaction requires, the hydrogen peroxide is used to oxidise any copper in the gold powders and then with the addition of the sulphuric acid the copper oxide, produced by the previous reaction, is dissolved.


I'm hoping that one of you will provide some details to the process so that we can all understand how it is different than piranha solution. Bickering back and forth without explaining the details isn't helping anyone and it just adds to the clutter.

Dave


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## solar_plasma (Oct 20, 2013)

martyn111:


> heating of this process to 120c has never been mentioned, nor is heating part of the process.



I have mentioned it. When you mix the two chemicals, heating is part of the process:

wikipedia:


> Mixing the solution is exothermic. The resultant heat can bring solution temperatures up to 120 °C. It must be allowed to cool reasonably before applying any heat. The sudden increase in temperature can also lead to violent boiling, or even splashing of the extremely acidic solution.



Lou:
Re: piranha and base piranha in refining?.


> No use in anything we do.


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## martyn111 (Oct 20, 2013)

I'm not going to be drawn into a P*ssing contest with anyone over this.
Solar, re read my post and you will see that i mentioned that the reaction is exothermic, so please explain your reply.
The full process has not been explained due to your insistance that conc sulphuric is the devils spawn although this is the same chemical used in the gold stripping cell.
You may be in a position that you use chemicals everyday in your work, therefore you should be aware that all chemicals if handled incorrectly are dangerous but can also be a very useful tool when used correctly.
Had you not jumped down Jon's throat the minute he mentioned conc sulphuric and hydrogen peroxide in the same sentence then a fuller explanation of the process could have been made.


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## Anonymous (Oct 20, 2013)

Right Ok Solar.

Here's the process (against my better judgement if the truth be known). When reading it I hope that you recall that you never asked WHAT I was doing, you made a load of assumptions based upon the chemicals involved. 

For reference please use all appropriate safety procedures:

Take your dirty Gold powder and place in a cleaned glass jar.
Cover to a depth of 1cm with distilled water. Measure the amount of water used. This should allow for the use of different sized containers.
Add Concentrated (yes the devil liquid) Sulphuric acid to the water to the same quantity as the distilled water previously added.
Stir gently with a glass rod to ensure it is fully mixed.
Add Hydrogen Peroxide from a pipette, one or two drops. 
You will see the gold begin to fizz slightly as the reaction occurs. At this point you will see blue liquid (Copper sulphate) start to enter to solution. This is the copper being leeched out of the gold.
Stir gently to ensure all the peroxide has been used.
Add another drop or two of peroxide, then rinse and repeat until no further reaction occurs and the solution doesn't get any more "blue."

It's controllable - by the limited use of the peroxide. It's not what you have been referring to in your previous posts.

Imagine that it's a lateral thinking approach to the standard forum use of AR. Nobody uses standard mixed AR - they DRIP the Nitric acid in so there is no excess. I welcome comments. 

Jon


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## solar_plasma (Oct 20, 2013)

I don't jump in anyones throat. There was nothing offending in what I said. If you two fellows try to make a personal thing of it, you can do it. I don't mind. I discuss facts. 

The problem is, you talked about conc. sulfuric and H2O2, never mentioned you really meant dilluted sulfuric. That is what you actually are using. Yes, it's amazing how fast it eats the copper. But as I said, even dilluted it is violent stuff, not to compare with sulfuric. And reread, what I wrote: 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).


Where do you two guys have a problem with this? 

I never said, it couldn't be used dilluted, - only that it is still extemely hazardous, if you don't know to handle it, not to compare with sulfuric under 100°C or AR, those are pussy cats compared to this tiger.

On the other side, what benefit do you have with it, it does the same thing in seconds, hot dilluted sulfuric would do in half an hour. Impatience could be a reason to use it. The more I learn about refining, the more I try not to be impatient.


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## FrugalRefiner (Oct 20, 2013)

Whew! Glad you guys got that out of your systems.

Jon, thanks for posting the details of your process. It's obviously quite different than piranha, though it starts with the same chemicals. I find the process interesting in the approach of adding the peroxide dropwise to diluted sulfuric acid, just like adding nitric in increments when making AR.

Perhaps now that the process has been described, we can get some others to opine on it.

Dave


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## butcher (Oct 20, 2013)

If you do not say what you mean,or explain your comments well, and you do not state details the best you can, or explain what you are trying to say in detail, you leave what you say up to assumptions, where the reader has to assume, or you leave your comment up to assumption of the reader, where you can be easily misunderstood.

Also with many of us here speaking different languages there are also problems with translating the messages, which can further lead to confusion.


Solar was assuming with safety in mind for other readers, and without better details what else would be expected, without more details many of us here concerned for others safety would do the same thing.

You should be clear of what you are talking about (as best as you can), especially when discussing a dangerous process, or one that someone can make assumptions of, and could become (in the wrong hands) a very dangerous process, with little details and assumptions of unclear statements, a very dangerous process could result getting a new member hurt or crippled for life.




I see no benefit to using the sulfuric acid (whether assisted with H2O2 oxidizer or not), on these gold powders, in fact I believe it would be a mistake, especially if this material came from electronic scrap, where any remaining lead in the gold would form an insoluble lead sulfate, contaminating the gold and making it brittle after melting.

With the normal process we use and the gold washing procedure of the gold wash we can eliminate lead as a soluble chloride in boiling hot water rinses.


I see no benefit at all to using sulfuric acid to dissolve copper (over the conventional copper II chloride leach), whether you are speeding up the process with a little O2 addition from H2O2 or not.
there are times where I choose to use sulfuric acid to remove base metals (sometimes even as a replacement for nitric acid a process I will not go into detail because of its dangers), but for general use I like the copper II chloride leach to dissolve copper (when nitric acid is not an option) especially for fine copper metal from electronic scrap, the chemicals are cheaper (for me), and I can rejuvenate the CuCl2 leach for very little cost, and reuse it again, this not only lets me dissolve more copper for less money but also helps to lower cost and trouble in the waste stream (although when I do make copper sulfate it is normally reused in other processes).

Actually I believe you can dissolve gold as a sulfate if the H2SO4 acid and H2O2 where concentrated enough (extremely dangerous process, which would just be stupid to try), but the gold would not stay dissolved long as a persulfate of gold, as I believe it would be unstable as a gold persulfate,. My thinking on this would not be much different than using the concentrated sulfuric acid gold deplating cell where gold is dissolved at the anode, but as the gold per-sulfate leaves the highly oxidizing environment of the anode area the unstable gold per-sulfate converts back to gold metal powder and sulfuric acid, also similar to this process in the electrolytic cell, a strong peroxymonosulfuric acid H2SO5 would likely passivate copper (with an oxidation layer) at least until the solution lost its overly strong oxidation power.

Again I see little benefit here with this method of using sulfuric acid to dissolve copper making copper sulfate.


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## Palladium (Oct 21, 2013)

solar_plasma said:


> Lou:
> Re: piranha and base piranha in refining?.
> 
> 
> > No use in anything we do.



I agree also!


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## Harold_V (Oct 21, 2013)

spaceships said:


> 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.


Please adjust your attitude. You were not "told off". We have a policy on this board to restrict any suggestions that can prove to be a bad decision on the part of the unknowing. Concentrated sulfuric is known to be quite hazardous, so the cautionary note was acceptable. We generally advise against its use, especially when heated. We also expect readers to speak out when they read anything that presents unnecessary risks. 

The real problem we have is having readers who often have little to no chemical training, and are not in tune with the hazards that may be present. For example, we are typically unwilling to discuss much about HFl, strictly because it presents hazards that can be life-threatening. 

Assuming you have a process in mind that tends to lean towards being rather dangerous, and you wish to discuss it to some end, you should be the one to present the warnings. Do not assume that because you have an understanding that others share your knowledge. They often do not. We do not endorse anyone's use of the board to promote a process that offers unnecessary risks. 

Harold


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## Harold_V (Oct 21, 2013)

I've tried to follow this _dog and pony show_, and am less than impressed. I'm at a loss to understand why you must re-invent the wheel? What possible reason would one have to use the sulfuric process? To think that ANYONE would spend as much time defending a process that has no real practical use, as has been expended on this one, is beyond my understanding. It is my opinion that this entire matter needs to come to an end. Do you get my drift? 

You want to wash your recovered gold with better odds of eliminating copper? Long before I'd choose sulfuric, I'd choose nitric (and I recommend that it not be your choice). The problem is, you're working with a substance that has been recovered from a chloride, so you risk dissolving some of the gold along with the unwanted base metals, which would even include lead, very unlike sulfuric. That, in and of itself, should be reason enough for this sulfuric process to be eliminated from use. I won't go in to the difficulty of eliminating all of the sulfuric after the wash has occurred. 

We've been through this before---and there's more than good reasons why we wash our gold as we do. We use the procedure we promote because it works (and damned well, if you don't see yourself as being clever, and avoiding doing it properly), and it offers the least possibility of risk. 

Get on with things of substance, and put your damned egos in neutral. 

Harold


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## Palladium (Oct 21, 2013)

In all my chemicals i fear and respect sulfuric the most. True it can be handled properly and safely, but i'm a man of probability. In a game of chance the sure way to beat the house is you don't play in the first place. The only time i use sulfuric is to remove lead. I've run a very successful hobby with just Hcl, nitric, smb, and urea. Some people don't even use urea, but with my batch sizes nitric acid is always in excess and solution volume is such that evaporation or use of a gold button is not feasible. Some people only need these three basic chemicals and you can produce quality gold time after time. A gold refinery can be had for very little investment compared to the returns. The wealth of the refinery comes not from it worth, but from one's knowledge.


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## JHS (Oct 21, 2013)

I have read that diluted sulfuric in a cell will desolve gold.
if you dilute sulfuric and add h2o2 would it not desolve gold,
and if sulfuric needs to be diluted,why not just start with
battery acid,already diluted,instead of 98% sulfuric.
I would like to understand these points.
thanks john


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## Lou (Oct 21, 2013)

Sulfuric acid doesn't dissolve gold unless another oxidizer is present.

That's part of the reason the sulfuric acid stripping cell works--it generates peroxysulfuric acid in situ which is a transient species that dies off, putting the gold back in ground state as a black/brown powder that will settle.


If you're talking about cleaning up gold after chemical reduction you need to consider several things:

1. Is it contaminated with silver chloride?
2. Is it contaminated with other base metals?
3. How was it precipitated-- copperas, SMB, oxalic?

If you suspect AgCl contamination, that's where an ammonia wash is indicated.
If you suspect other base metals, warm, 70% sulfuric acid is highly effective at removing those, including Pd.

If it was precipitated with copperas, expect iron contamination, especially if solution was dilute and not highly acidic. If it was reduced with SMB, expect palladium and/or copper (I) chloride contamination, if it was reduced with oxalic but was a dirty solution, expect copper oxalate contamination (and other metals that form insoluble oxalates, particularly rare earths and alkaline earth metals (Ca+2).

No need to use peroxide in any situation for cleaning up Au, unless you're redissolving it!


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## solar_plasma (Oct 21, 2013)

So,

if I have used SMB (gold (medium brown), source e-scrap, possibly contaminated with everything common to e-scrap)

washed with hot 36% HCl (Pb, Cu, edit: all or almost all other base metals)
washed with boiling water (Pb)
dissolved all AgCl with NH4OH (then made the filtrate acidic again with HCl to avoid unstable silver compounds and precipitated AgCl)

will there be anything left I could remove with


> warm sulfuric 70%


?

Isn't the Pd already dissolved in HCl?

EDIT:
Already answered:


> If you suspect other base metals...



Thanks!


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## 9kuuby9 (Oct 21, 2013)

solar_plasma said:


> So,
> 
> if I have used SMB (gold (medium brown), source e-scrap, possibly contaminated with everything common to e-scrap)
> 
> ...



Possibly Pd, but it depends on how clean your feed-stock is and what it originated from.

I haven't fully read the thread thoroughly but I haven't seen the Karat Inquartation method? (I know it is supposed to be intended for karat scraps) Which is also a good alternative To almost fully digest all those base metals, Ag and Pd with hot 35% nitric acid.

From Their you can keep adding a fresh solution of nitric acid until it stops reacting or doesn't gain a color. (do keep those Nitric leaches for future treatments) dissolve Au in AR, drop with SMB or ferrous sulfate. Apply harold's Washes and then redissolve and precipitate with Oxalic. You should now have at least 999+ fine gold; Do also note that clean glassware and proper rinsing and washing also makes a great difference in the concluding purity of the material.



Lou said:


> If you suspect other base metals, warm, 70% sulfuric acid is highly effective at removing those, including Pd.


 Do you possible know the solution color of Palladium, dissolved in a halide-free, acidic medium, like aqueous Sulfuric acid? and any solubility data in water?

Any help is always appreciated! :mrgreen:


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## solar_plasma (Oct 21, 2013)

Full strength HCl washes are starting to make sense to me: I just read even PbCl2 is soluble in conc. HCl :shock: so all basemetals are more or less soluble in it. ....yes I am it bit slow sometimes :lol:

At least as a solid Pd (II) SO4 is red-brown: http://de.wikipedia.org/wiki/Palladium(II)-sulfat


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## 9kuuby9 (Oct 21, 2013)

solar_plasma said:


> Full strength HCl washes are starting to make sense to me: I just read even PbCl2 is soluble in conc. HCl :shock: so all basemetals are more or less soluble in it.


More or Less, yes.



solar_plasma said:


> ....yes I am it bit slow sometimes :lol:


 Well a least you know what you are reading. While some don't :lol:


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## freechemist (Oct 25, 2013)

Hi 9kuuby9,

The colour of a Pd-solution in aqueous sulfuric acid, obtained by oxydation of Pd-black with HNO3, is similar to the colour of a solution in e.g. 1:1 HNO3/H2O, like shown in the pictures of your post "Refining Palladium Concentrates" http://goldrefiningforum.com/phpBB3/viewtopic.php?f=51&t=19352. Concentrated Pd-solutions with 100-200g Pd/liter can easily be obtained.

Regards, freechemist


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## 9kuuby9 (Oct 25, 2013)

freechemist said:


> Hi 9kuuby9,
> 
> The colour of a Pd-solution in aqueous sulfuric acid, obtained by oxydation of Pd-black with HNO3, is similar to the colour of a solution in e.g. 1:1 HNO3/H2O, like shown in the pictures of your post "Refining Palladium Concentrates" http://goldrefiningforum.com/phpBB3/viewtopic.php?f=51&t=19352. Concentrated Pd-solutions with 100-200g Pd/liter can easily be obtained.
> 
> Regards, freechemist




Thank you for the reply, I'm really grateful for the information you provided.
Because I think their isn't any or almost any information around the forum regarding palladium dissolved in a aqueous medium like Sulfuric acid.

I dissolved Pd in sulfuric acid with Caro's Acid, and ended up with a very dark brown solution. I did test it with stannous chloride, It firstly gave a dark brown spot and then became dark green after a while, indicating a concentrated presence of Pd.

How do you suggest on recovering Pd from a sulfuric solution? Should I cement the Pd or is their an other process involved in directly refining Pd from that solution? The solution contains a very little amount of base metals (around 1-5%) 

It would be very appreciated if you would like to elaborate a little further on the subject of Palladium dissolved in a sulfuric medium, because their is so little information around here on the forum.

Kind regards,

9kuuby9


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## Lou (Oct 25, 2013)

If the solution is relatively clean (no Au or Ag which should be removed prior), you can perhaps concentrate as much as possible but not over much or you will see PdO form if it begins to fume. Then partially neutralize with caustic soda until the pH is ~1. At that point you can take it into c. aqueous ammonia and form [Pd(NH3)4]2+ and filter to remove any precipitated hydroxides of base metals and business as usual. One thing to consider is that the hydroxides produced, much like those during any hydrolytic purification procedure, WILL contain values and should be recycled back into the digestion circuit. 

Perhaps you could make another very nice picture post under its own thread?


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## 9kuuby9 (Oct 26, 2013)

Thank you Lou!

If I were to have some Silver sulfate in my solution, how should I proceed? Would be adding HCl in increments until the Silver has precipitated as AgCl be an option? But them the problem still Persists, since both Silver sulfate and Silver chloride have a very small solubility and is considered among the insoluble salts. Or won't be that very small amount of soluble Silver sulfate be a problem?
I know that the cleaner the stock material is the greater the final purity will be.

Does the c. aqueous ammonia have to be warm to fully convert the palladium in aqueous sulfuric acid into [Pd(NH3)4]2+?

Thanks again for the consideration, I have stored those hydroxides just to be sure. Would it suffice bringing the metal hydroxides into an acidic medium forming a salt and recover any value from their or are their additional steps involved?

I will make another very nice picture post under my existing thread on refining palladium concentrates in the future, Platinum metals are really fun! :mrgreen:


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## 9kuuby9 (Oct 28, 2013)

Some updates on the process, Well sorry for Hijacking this post but I guess all the good things are scattered all around in this forum. :mrgreen: 

As per Lou's Suggestion, I increased the ph to 1 with caustic, Followed by additions of c. aqueous ammonia.

After reaching the ph of 4-5 the solution started to boil heavily, Which brings me to think that their is a lot of free sulfuric acid left in the solution?

So I decided to evaporate down the solution, A lot of white crystals formed; My guess would be Ammonium sulfate (NH4)2SO4 ?

Is their any method to see if their is any free sulfuric acid in the solution? or a plausible means of ridding it?

Thanks in advance!


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## Lou (Oct 29, 2013)

It cannot be boiled off. The idea with partial neutralization is to keep your solution volume down during the ammonia addition (very easy to start with 200 g/L Pd and end up with 50 g/L).


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## 9kuuby9 (Oct 29, 2013)

I ended up with a dark brown hydroxide at a ph of 8, I tested the solution and it gave a negative result. Which means the hydroxide is probably Pd? I've reintroduced it to an acidic environment and rested the solution and it now tested positive for Pd.

Palladium hydroxide precipitates at a ph of 11 of I'm not mistaken?

It was first added NaOH to a ph of 1, then heated the solution and added aqueous ammonia until the reaction became too violent.

after letting it cool off, the dark brown hydroxide precipitated.

I don't know what went wrong in the process but something did.


I'm going to cement the Pd with Al and see how it works out.


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## Lou (Oct 29, 2013)

Palladium oxide starts precipitating around pH 4 and is largely done at pH 6.5.

The hydroxide will re-dissolve in HCl and you can try again.


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## freechemist (Nov 13, 2013)

It seems to me, that a whole bunch of new questions has emerged. I will try, to answer some, even if they have nothing to do with the title subject ("Final Refining Gold Brainstorming"). What follows is based solely on our own laboratory experiences and observations.


> *9kuuby9 wrote:*
> I dissolved Pd in sulfuric acid with Caro's Acid, and ended up with a very dark brown solution. I did test it with stannous chloride, It firstly gave a dark brown spot and then became dark green after a while, indicating a concentrated presence of Pd.


Pd-black dissolves in sulfuric acid by oxidation with nitric acid, giving an intensely orangered-brown colored solution. Only a slight excess of HNO3 (ca. 10%) has to be used, assuming quantitative reduction of N(V) in HNO3 to N(III) in hypothetical HNO2, and quantitative oxidation of Pd(0) to Pd(II). Most intriguing in these digestion reactions was the fact, that only small quantities of nitrogen oxides escape, even on prolonged, strong heating. Adding small portions of sulfamic acid to well stirred, hot samples leads to fizzing, and finally to a colour-change to a more brown and less orangered colored solution.


> *9kuuby9 wrote:*
> How do you suggest on recovering Pd from a sulfuric solution? Should I cement the Pd or is their an other process involved in directly refining Pd from that solution? The solution contains a very little amount of base metals (around 1-5%)


There are several ways: One, as Lou suggests, forming first [Pd(NH3)4]2+, followed by crystallization of (NH3)2PdCl2 the known usual way. Another possibility is cementation with formic acid in excessive HSO4-/SO42--buffered solution. Partially neutralize with NaOH to a pH of ~2 (maximum). Add a small excess over the stoichiometric amount of formic acid and boil under reflux until only metallic Pd and a colorless mother liquor remain. Usually base metals will remain in solution. A third possibility consists in the crystallization of K2PdCl6, which can be worked up further the "ammine-way", or, if pure enough, by first reducing to K2PdCl4, followed by cementation with formic acid in an acidic HSO4-/SO42--buffer.


> *Lou wrote:*
> If the solution is relatively clean (no Au or Ag which should be removed prior), you can perhaps concentrate as much as possible but not over much or you will see PdO form if it begins to fume.


I made a similar observation by heating a solution obtained by oxidation of commercial Na2[Pd(SO3)2]*2H2O with H2O2 in excvessive aqueous sulfuric acid.


> *9kuuby9 wrote:
> *If I were to have some Silver sulfate in my solution, how should I proceed? Would be adding HCl in increments until the Silver has precipitated as AgCl be an option?


This would definitely not be an option. Both, Pd and Ag are strong competitors, Pd maybe even stronger, "fighting for every chloride ion entering the solution". The only way to attain a clean separation of Ag from Pd needs excessive chloride (e.g. as HCl), that means more than stoichiometrically required, to form [PdCl4]2- and AgCl quantitatively.


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## Palladium (Nov 13, 2013)

If no one has told you this freechemist let me be the first to say " Having you here on the board is a real asset."
Both you and Lou bring a great deal of knowledge to this form with your academic educations. Even though i only understand only part of what you say i can see the knowledge and wisdom in your educational field of studies. 8)


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## Lou (Nov 13, 2013)

I agree that freechemist is very, very knowledgeable. 

One thing to emphasize--a degree isn't very helpful in refining. I don't think there's any amount of school that can be substituted for reading and then doing it.


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## Palladium (Nov 13, 2013)

I agree! The knowledge side comes from education. The practical side comes from doing. 
I'm the monkey see, monkey do type. This might not make sense but i'm a better teacher than i am a learner. Teaching and relating comes easy for me, but first learning that knowledge so i can relate it is sometimes troublesome.


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## 9kuuby9 (Nov 15, 2013)

Thank you freechemist, your help and contribution is appreciated as always. :mrgreen: 

Now I have some more information regarding the refining of PGM's to add to my notes. 8) 

Can you also elaborate for us the pro and cons of oxidizing Pd with nitric acid in a sulfuric buffer? I somehow feel that you prefer this method over the classical Nitric buffer, Their might be a sound reason behind this.
Most of the literature on this subject (That I know of) covers a very small part on how to process PGM's. The first thing I could say it to limit Noxx fumes and the use of nitric.


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## freechemist (Nov 18, 2013)

> *9kuuby9 asks:*
> Can you also elaborate for us the pro and cons of oxidizing Pd with nitric acid in a sulfuric buffer? I somehow feel that you prefer this method over the classical Nitric buffer, Their might be a sound reason behind this.


There is, indeed, a very sound reason behind. Digestion in nitric acid alone leads to solutions, whose further working up needs evaporation of copious amounts of excessive (and unnecessary) nitric acid, like elaborated in my post to "_Nitric and Palladium_".
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=11490&start=20#p198707


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## 9kuuby9 (Nov 18, 2013)

Thank you for the proper elaboration freechemist, Yet other precious knowledge I need to take into account. 8) 

Have you also came to the conclusion that Palladium sometimes tends to passivate in nitric acid? Especially when the solution is exhausted from Nitric acid? Because When their is still un-reacted Pd left in the reaction vessel and you then add more nitric acid to the vessel, their somehow is no visible reaction progressing.

I have just read your post and it's very self explanatory. (Edit)

However do you have any Idea why it happens? Maybe due to it's catalytic properties?


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## goldsilverpro (Feb 2, 2014)

From links somewhere on this forum, I just watched 2 videos on using weak sulfuric (H2SO4) + hydrogen peroxide (H2O2) to dissolve copper and I am sold on it as a replacement for AP. I feel it can work safely. One I saw used straight 12% H2O2 and 37% sulfuric acid (battery acid) solution (he said, because of the foam, to use a container 10 times bigger than the solution volume). The reaction was vigorous and generated a lot of heat and foam. Another video used about the same mix but diluted it considerably. It worked, but slowly. Somewhere in the middle is maybe the right answer.

This is a weak piranha solution. The "real" piranha solution uses concentrated sulfuric (97%) - 3 parts, and 1 part of, say, 30% - 35%hydrogen peroxide. It's used for such things as super-cleaning glassware. If 50%, or higher, H2O2 were used, an explosion could occur (Wikipedia) when pouring the strong H2O2 into the 97% sulfuric. However, it seems that, if you use a dilute solution, these dangers fade away. Also, once you get it mixed, the dangers seem to fade.

Pros and cons of dilute H2SO4/ versus AP

Pros: 

1 - Fumes are far, far less than AP or Nitric and I would bet it is a lot faster than with AP. The fizzing is bubbles. All bubbles are gases, coated with the solution from whence they came. These get into the air, burst, and fill the air with minute drops of H2SO4 solution. Weak sulfuric in the air will rust steel and, if it's strong enough, it will force you to vacate the area, pronto.

2 - You end up with a copper sulfate solution, which is a good copper compound to work with. For example, if you evaporate the solution, near boiling, until crystals barely start to form, allow the solution to cool, and then chill it, you can remove about 80% of the copper as cupric sulfate crystals. Then, you analyze the solution for sulfuric (easy) and, maybe for H2O2 (not too hard), add some chemicals, heat it up, and dissolve some more copper. I believe you could re-use the solution.
3 - 

Cons: 

I can't think of any, if it works well.

Someone really should play with this. Find the best mix. How fast? Etc, etc. Be safe.


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## solar_plasma (Feb 3, 2014)

> Find the best mix. How fast? Etc, etc. Be safe.



First time I used this on silver/copper, I wasn't prepared and was not aware of it's a weak piranha solution, I learned very quickly to have respect of it and even more when I short time after got aware of what it actually is and read about it. It is my impression, that it works fast also because it is getting quite hot and works slowlier, when it is cooled down again. So, maybe the most dilluted version could be fast, too; if it is heated. Just a possibility in order to find the best compromise between safety and effectivity....


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## sharkhook (Feb 3, 2014)

Just a random thought from someone who once mixed concentrated sulfuric and 3% H2O2. I am glad now there were no metals involved but the glass was very clean. What if a solution of weaker H2SO4, (battery acid) and 3% H2O2 were used, In a large container. Myself, I am very leery of anything, especially acids, that foam up. But the use of the diluted acids H2SO4 such as that used in batteries, and the 3% version of hydrogen peroxide, a formula similar to the AP system could be evolved. I have no idea if I would use it anytime soon, I just see it as possibly another option for those with more experience.


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## solar_plasma (Feb 3, 2014)

The point is AP, which in fact is a misleading term, it should be called something like Steve's(et al.)-CuCl2-regenerative-copper-etching-system, is reusable. Given the case, that you need CuSO4 for any other purpose, H2SO4 might be a viable option and given the case you have to save time for any reason,the very dilluted "piranha" might be an option to those, who know to make and use it safely.

It is just no AP, it is not similar to AP in any way and people should be aware of that.

Also anyone shouldbe aware of, it makes only sense in the state of recovery. When used for washes, it has great disadvantages, when for example lead, barium or other unsoluble sulphates could be involved. There is in my opinion no alternative to the Harold/Hoke-Washes with HCl, when we talk gold. A special case might be silver powder with only copper as a contaminant, this could be worth a discussion.


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## freechemist (Feb 4, 2014)

> *Solar_plasma* writes: The point is AP, which in fact is a misleading term, it should be called something like Steve's (et al.)-CuCl2-regenerative-copper-etching-system, is reusable.....


This statement is essentially true. The so called AP-method is limited on aqueous HCl-systems. Excessive HCl is an integral part of "AP-solutions". It helps, to held Cu(I)-chloride, CuCl, containing Cu(I), the reduction product of Cu(II)-Chloride, CuCl2, as anionic chloro-complex, [CuCl2]-, in solution, thus keeping it available to reoxidation to Cu(II)-chloride, CuCl2, through reoxydation by oxygen from the air, introduced through the air-bubbler. Excessive HCl also delivers the hydrogen-ions, H+, needed, to form water out the reduced oxygen from the air.


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## Geo (Feb 4, 2014)

AP, acid/peroxide is actually a refining tool. hcl alone will not dissolve gold but it will hold dissolved gold in solution. by adding H2O2 (an oxidizer) to hcl in the presence of gold, the gold will go into solution. it works better on fines and micro-millimeter foils. due to the electromotive series of metals, metals higher in the reactivity series will dissolve first so when using AP to refine gold powder, it should be almost pure to begin with.


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## solar_plasma (Feb 5, 2014)

I wrote:


> Also anyone shouldbe aware of,* it* makes only sense in the state of recovery.



I meant H2SO4 as a tool to remove basmetals, while I dared to state this since it is not only my present point of view, but also already was expressed by others in more or less similar form. And even this might not be always true, - but at least in most circumstances. Ofcourse I agree with you, Geo.


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