# Agua Regia not dropping gold after saturation with smb



## Jovane (Dec 11, 2018)

So...this is my first attempt at e-scrap gold refining and I picked up a problem. No I did not know about Hoke's book untill I found it yesterday on this forum.....most of my learning curve was through youtube videos.....obviously they don't say what to do if things go wrong. .....now. ...I read a few replies fro questions on this forum and found a few remarks by wise cracks who don't appreciate the fact that they once were where I am now and got a bit insulting......so ....lets cut the bad remarks and please help out.....this is why this forum is there,isn't it? I made two batches.... one from plated pins and the other from 8 kg of cellphone scrap....recovering the flakes went ok......made agua regia 3 to 1 hcl and nitric for the pins batch ....added to the gold flakes and it dissolved fairly quickly and turned clear yellow.

With the cellphone batch I added hcl and slowly. ...bit by bid added nitric till flakes disolved.....it turned a murky yellow. ...left it for 2 hours.....added smb powder slowly to both batces indicidually..... the pins batch took lot of smb but would not drop gold....it turned light brown......the cell batch took lots of smb untill saturated and turned darker rust brown .. would not drop as well......I did not use heat on both batches...what went wrong .... I'm waiting for tin to disolve to do stannous test.....all gold flakes is dissolved si it must be in solution.....see photos attached


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## anachronism (Dec 11, 2018)

I'm not seeing where you denoxxed your solutions within your process.


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## butcher (Dec 11, 2018)

No reason to be embarrassed, we all started at the beginning.

Read Hoke's (well you know that now), she speaks of removing nitric acid from solution through careful evaporation with heat, on the forum you will learn about Harold's method of adding gold or using sulfamic acid (a tile grout cleaner sold at Walmart) to deNOx the solution.
now. ...I read a few replies fro questions on this forum and found a few remarks by wise cracks who don't appreciate the fact that they once were where I am now and got a bit insulting......so ....lets cut the bad remarks and please help out.....this is why this forum is there,isn't it? 

Jovanne, why walk around with a chip on your shoulder? Are you so sensitive?
Relax, members here spend their time sharing and trying to help new members like you, but we may not always tell you what you wish to hear, so we may by mistake bump your shoulder (hopefully you can keep the balance of the chip).


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## Jovane (Dec 11, 2018)

I lost the chip in embarrassment. .....so next question...when the gold did not drop I kept on adding smb.....lots of it....will it be a problem if its over saturated with smb.....or can I just start heating? Boiling point or jus medium heat?


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## anachronism (Dec 11, 2018)

Simmer it until there's no more brown fumes coming from it. 

Then try again with SMB. Obviously make sure you have gold by testing with Stannous.


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## Jovane (Dec 11, 2018)

:shock: can gold dissapear after it was desolved in agua regia?


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## 4metals (Dec 11, 2018)

> :shock: can gold disappear after it was dissolved in aqua regia?



It won't disappear but it can easily be lost. You are looking for grams of gold at most and the volume of your solutions indicates you added sufficient aqua regia to dissolve ounces. Making stannous chloride test solution is important to the process because the stannous test will allow you to "see" quantities of gold that your eyes cannot see. 

By mixing your aqua regia at 3:1 you easily added excessive nitric acid. The result of not eliminating that free nitric from the solution is that every time you drop the gold out of solution, the free nitric acid reacts with the hydrochloric acid and the newly precipitated metallic gold and the gold re-dissolves. So it is easy to mis-interpret the results of the gold not coming out of solution visibly with the gold disappearing. That is why you will learn to ultimately trust the results of stannous chloride testing to determine if your gold is in solution. 

Your problems are typical with members new to refining and are easily overcome with both reading and asking questions. In the long run experience is the greatest teacher. With photo's and descriptions of what you did, the members of this forum can guide you in gaining the experience you need to understand this process. If you do the work required on your part, I am confident our members will not let you down. 

Welcome to the forum


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## butcher (Dec 11, 2018)

can gold disappear after it was dissolved in agua regia?

I do not disagree with 4 Metals, but I guess I will just say if a magician held a gold coin in his hand and then wet it to where I could no longer see it I would say it disappeared in front of my eyes, I know it is somewhere but I cannot see it anymore, in chemistry it is like magic (at least in my small and simple mind).

Yes (in my mind), gold can disappear after being dissolved, at least we cannot see it anymore, it is not magic but chemistry, we cannot see it but it is still there in solution but not as the same gold we held in our hands before dissolving it. When gold is in the metallic state it is a lump of gold atoms with a full shell of electrons. 
When we dissolve the gold we Oxidize (Oxidation the loss of electrons) the gold in a chemical reaction where the acids involved in this reaction are Reduced (Reduction a gain of electrons), so in this reaction the atoms of the gold is oxidized (the atoms of gold have lost their electrons) to form a salt of gold (positive ions called Cations) and the acid is reduced to a salt of the acid (negative ions called Anions) together these positive and negative ions make up a salt of the gold in solution we call gold chloride Au+Cl3-.

Gold chloride will tint the solution yellow if dilute to red burgundy when very concentrated, but we cannot see the gold as it basically disappears from our eyesight, and other metals will also give color to a solution, iron ions in solution can look like gold (yellow) or look like copper (green) or red and several other colors depending on its oxidation state... With other metals giving colors to a solution much easier than gold the gold in our solution basically disappears (at least from our eyesight) the gold in solution cannot be seen but it can be detected. The color of a solution is not a very good way to tell what is in solution, although it can sometimes be an indicator, testing is the only way to verify what the color actually comes from or what metal ions are in solution...

How do we detect for gold in solution if we cannot see it?
Well, we just use a little magic we call chemistry.
We have to make the gold reappear to our eyesight.
How do we do this?
We have to give the gold ions back their electrons so they will make atoms of gold with full orbitals shells, and we have to get enough of these small gold atoms to join together with each other in a big enough clump that we can see them with our naked eye (make the gold reappear magically well chemically but magic sounds more fun), to do this we must Reduce the gold giving it electrons, we do not need to reduce a large amount of gold to see it in solution we can use a tin salt called stannous chloride, which reduces a small portion of the gold ions in solution to a certain size of gold in nanoclusters of atoms of reduced gold called colloidal gold which give a purple color to the solution called purple of Cassius, even though these clusters of gold atoms are actually metallic gold with full shell of electrons in the atoms of gold, the clusters colloid and will not grow large enough to precipitate from solution the cluster gain an electron charge which makes them repel other clusters of gold atoms, ad so are virtuall locked in a cycle which is not easily broken (but thats a subject for another question).

So gold does disappear from our eyesight, but the gold is still in solution as gold atoms with missing electrons or gold ions a salt of gold. 
Stannous chloride SnCl2 can make the gold reappear in solution as a purple colored colloidal solution we call the purple of Cassius test, where the clusters of gold atoms color the solution violet in the test.

Well if I have seen gold and someone put it into a solution, for my eyes it disappears.
But just because it disappears it does not mean it is gone.

Your gold will disappear from your possession if you do not know where it is and you throw it out with your waste, with stannous chloride we can detect very small amounts of gold in solution (by a reduction reaction), which we can see with our eyes.

Without using the stannous chloride test you are just guessing, and have no real idea if gold is in solution or not, this is why we call SnCl2 the eyes of the refiner, it allows us to make the gold reappear to our eyesight.

Like a magician I can make gold disappear where you cannot find it-- unless you also are a magician and can make it reappear with magic (chemistry), your magic will come with a chemical reaction using stannous chloride, or ferrous sulfate...

I do not believe in magic a magician cannot make anything disappear (even gold), he can hide it or change its form or make it into something else, but he cannot make it disappear.


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## 4metals (Dec 11, 2018)

In my years in this industry, I have made considerable profit from refiners wastes. Solutions or sludges that were holding (sometimes considerable) values which the refiner did not recover because it wasn't apparent (or visible) to the refiner in the waste. Did it disappear? Well chemically it was still there but to the unaided eye, it wasn't. So while it may be a play on words, I saw it, they didn't, I made out on the deal.


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## Jovane (Dec 11, 2018)

Thanks 4metals and Butcher....I am really lerning a lot....so my nexy step is to heat both solutions moderately and evaporate to +- half ......add carefully little bit of sulphuric acid to get rid of nitric in solution and repeat smb process (or will it precipitate with the oversaturation in the first place). Am I right in this (still waiting for tin to dissolve in hcl to do stanous test)..... the cell batch has lots of gold in solution that I know.....
Thanks again for friendly advice.....


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## Arbentor (Dec 11, 2018)

Jovanne,

Make every effort to read comments on the forum carefully and always be accurate or exact when using chemical names.



Jovane said:


> ......add carefully little bit of sulphuric acid to get rid of nitric in solution



*Sulfuric acid is not what you need*.

Please re-read Butcher's comment:



butcher said:


> Read Hoke's (well you know that now), she speaks of removing nitric acid from solution through careful evaporation with heat, on the forum you will learn about Harold's method of adding gold or using sulfamic acid (a tile grout cleaner sold at Walmart) to deNOx the solution.



Perhaps you meant to say *Sulphamic Acid*?


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## butcher (Dec 11, 2018)

Gold will not precipitate with evaporation or concentration, as long as free nitric acid is left the gold not precipitate or will reoxidize (redissolve back into solution) as the free nitric takes electrons back from the gold.

The gold ions or the gold salt will not precipitate until you give the missing electrons back to the gold ions with a reducing agent like a metal lower in the reactive series (zinc copper etc.), or a chemical reducing agent like sodium sulfite, sodium metabisulfite some other sulfite, ferrous sulfate (copperas), oxalic acid, sulfur dioxide gas...
note that the reducing agent gives up electrons to the gold ions (and itself is oxidized as it gave up electrons) as the gold ions gain electrons to fill the atoms orbital shell the gold atoms clump into clusters gaining in size until these clusters overcome gravity and sink in solution as a light tan to brown powder if fairly pure or to a black powder with base metals involved in the precipitant...


Depending on how much unreacted nitric involved will depend if evaporating to only half volume will do much good. If you only have HNO2 in solution left the single evaporation may do the trick, if much free nitric HNO3, you may need to evaporate to almost a syrup, add a tiny bit of HCl to rewet (and help convert nitrate salts to nitric and continue to evaporate back down to a syrup, doing this three times will normally remove all of the oxidizer in solution, the first evaporation takes the longest to reduce the volume the second and third evaporations do not take long because volume has already been reduced so much..



If base metals ions like copper are involved these base metals can form nitrate salts, adding acid can reform nitric in solution.

Sulfamic acid H3NSO3 found in the hardware section sold as shower grout haze cleaner will remove nitrous and nitric acid from solution.

HNO2 + H3NSO3 --> H2SO4 + N2 + H20
HNO3 + H3NSO3 ==> H2SO4 + N2O + H2O
with sulfuric acid formed in solution we can remove lead as an insoluble sulfate salt.
PbCl2 + H2SO4 --> PbSO4 + HCL 
Insoluble lead sulfateand hydrocloric acid is formed from the above reaction.

Urea is not only dangerous but cannot remove nitric acid, although it can remove nitrous acid from the solution.

Adding a button of gold, this consumes nitric acid as the gold dissolves into solution, this with heat and possibly some evaporation works extremely well.


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## anachronism (Dec 11, 2018)

butcher said:


> Urea is not only dangerous but cannot remove nitric acid, although it can remove nitrous acid from the solution.



Would you expand upon this please?


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## butcher (Dec 11, 2018)

In pure concentrated nitric acid is clear, with more dilute acid or when we use nitric it can break down into solution as HNO2 nitrous acid, and with decomposition forms NOx gasses such as NO NO2 in solution giving color to the solution and clear (NO gas) and red gases (NO2 gas) from the nitric decomposition.

With pure fuming nitric acid one way to purify it and remove the HNO2 and NO2 from the solution is to add urea to the pure fuming nitric acid, this removes the Nox(NO2) but does not destroy the nitric acid.

I am at a loss of how to explain but urea will remove the NO2 from solution but not the nitric acid.

Urea and nitric acid will form urea nitrate an explosive compound, although more dangerous as a more dry salt it has been known to explode in solution when heated...


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## anachronism (Dec 12, 2018)

Are you saying that Urea does not effectively denox a solution Richard?

Or are you saying that it does, but it's via a few more steps than are apparent? 

Jon


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## Jovane (Dec 12, 2018)

Butcher.......I'm in an unfortunate position that I stay on a mission station in the bush in Mozambique (missionary ) where things are not readily available (bare with me) Im trying to make a batch of stanous chloride....I got these crystals feom a friend saying he thinks it is tin....I put 2gm in 30ml of HCL yesterday.....the solution does not bubble and turned light green....but does not look if the crystals desolves.....the crystals are grey/silver and are quite heavy....does it look like tin (stupid question if you can not analyse).... how long does it take for such crystals to dissolve (or am I in too much of a hurry?)

Secondly I read feom some site that you can disolve solder with tin in it (see photograph).... is that true....if so how much solder and how much HCL....thanks for your patience and very informative input.......


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## Jovane (Dec 12, 2018)

Crystals and solder


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## Jovane (Dec 12, 2018)




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## g_axelsson (Dec 12, 2018)

Whatever those crystals are, they are not stannous chloride. Stannous chloride is a white solid or a clear water solution.

Stannous is easy to do, just put some of that solder in a small beaker and add HCl. If it all dissolves add some more tin.
You might want to melt the solder first to remove any flux in the center, a lot of solders comes as a tube with flux in the core. I don't think it would harm the stannous but it could make it cloudy.
There are a ton of posts on how to make stannous on the forum.

As for urea, I have never used urea and I don't see any reason to do it. Classically, urea reacts with nitric acid to form urea nitrate, a water soluble explosive compound. To me it shows that the nitrate ions are still in solution and whenever the solution is acidic there will in fact be nitric acid in solution. Combine it with HCl and you have at least a weak aqua regia that can make life a misery for a refiner. Just the risk of that to happen is enough motivation for me to use any of several methods to denox my gold solutions without using urea.

Göran


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## Jovane (Dec 12, 2018)

Göran...I did mention those crystals are supposedly TIN........Which as far as I understand is also stannous chloride if desolved in HCL.....or am I missing something....

Jovane..


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## Dr.xyz (Dec 12, 2018)

Why not just disassemble any old broken electronic device made in the last 10 years, probably made with lead-free solder?

With these 3rd world countries, they can't just go to the hardware store and get "X", most likely there is only hammer and nails to choose from.


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## Jovane (Dec 12, 2018)

Butcher.....I happened to come across this solution at a small hardware (the only one where I come from) ....is this good to denox ....rather ask and make sure than putting scrap in and more scrap out.......


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## Jovane (Dec 12, 2018)

The first 3 photos is one product (grout/tile cleaner) and the other to remove grout from tiles....
Which one is best.....


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## Dr.xyz (Dec 12, 2018)

You don't have enough knowledge and skills to even start dreaming of refining.

Simple as that.


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## Jovane (Dec 12, 2018)

Dr xyz.....you don't even have the skill to be on this forum if that is your attitude......learn a few lessons from Butcher on compassion for new beginners...where you once were I bet.....after all...what is this forum for..... definitely not for guys like you hammering down on someone willing to learn.... remind me not to take advice from you with your facebook comments.....bless you in any case....


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## Dr.xyz (Dec 12, 2018)

Just pointing out that you started doing things in the wrong order. Studying and learning comes first, before you touch any kinds of chemicals.

If you had done that, you would not be in this messy situation, OK?


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## butcher (Dec 12, 2018)

Are you saying that Urea does not effectively deNOx a solution Richard?
Or are you saying that it does, but it's via a few more steps than are apparent? 
Jon
My understanding.
How can I say this, or explain it??? 
Urea can remove the decomposition products (NOx) from nitric acid, but it does not destroy the nitric acid.
Red fuming nitric ( with decomposition products NOx) which makes the acid red from the gases of decomposition If concentrated H2O2 or urea is added will make pure white fuming nitric acid.
Urea and nitric acid will make urea nitrate.

Urea can remove the decomposition products of nitric acid (NOx) from an aqua regia solution (as long as free nitric acid is not involved or at least is very minimal). So Yes it will de-NOx a solution of aqua regia (remove the NOx or decomposed nitric acid products in solution.
But it will not destroy the free nitric acid in solution.

Urea and nitric acid form urea nitrate in solution.
(H2N)2CO + HNO3 ==> (H2N)2COH(+) + NO3(-)
or written differently
CO(NH2)2 (aq) + HNO3 (aq) → (NH2)2COHNO3 (s) 

some formula's used for urea nitrate
(NH2)2COHNO3 
CH5N3O4, 
(H2N)2COH(+)

urea nitrate is not very soluble in water and crystallizes easily.

HNO2 nitrous acid is one of the decmposition products of nitric acid (HNO3)
Urea and nitrous acid (de-NOx)----> forms gases nitrogen (N2) and carbon dioxide (CO2), and water
H2N-CO-NH2 + 2 HNO2 + ==> CO2 + 2 N2 + 3 H2O



urea in a solution of PGM's can form some ammonia complexes with platinum which will inhibit their drop with ammonium chloride.


Urea can deNOx the solution, but it will not remove nitric acid, excess urea forms urea nitrate ( a dangerous explosive dry salt and with possibly dangerous in situations of boiling acid solutions under certain conditions). Debatably Useful in refining ( and then only if free nitric acid is Not involved in the aqua regia solution, as when minimal nitric is used and only the decomposition products of the former acid were previously involved such as NO, NO2. HNO2...
Urea can complex with Platinum giving trouble recovery with ammonium chloride.

Urea good as fertilizer but in my opinion is just dangerous and useless as a way to remove the oxidizers from our aqua regia solution.


Maybe someone with some chemistry background can help me explain this better.


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## Jovane (Dec 12, 2018)

Hi Butcher .....any comments on the first photograph of tile kleaner as you suggested. ..it does contain sulphuric acid.......


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## Jovane (Dec 12, 2018)

Dr xyz......I'm not perfect yet...but striving to be better tomorrow...... I made a few mistakes but I bet my next batch will be flawless with all the input of the nice people that gave positive input overlooking my stupidity.....learning by mistakes are the best teacher.... forgive you bro...


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## FrugalRefiner (Dec 12, 2018)

Jovane, sulfuric acid does not deNOx a solution. You need sulfamic acid.

Sulfuric acid is useful to remove any dissolved lead from your solutions, precipitating it as insoluble lead sulfate. A nice side benefit of using sulfamic acid is that one of the byproducts is sulfuric acid.

In this pursuit, the slightest differences in chemical names are very important.

Dave


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## anachronism (Dec 12, 2018)

Thanks for trying Butcher- to be honest I was trying to get my heads around it myself. 

I was trying to work out whether it was one of those equilibrium reactions whereby as the Nox was used up more Nitric broke down therefore it effectively reacted with all of the free Nitric over time albeit in a "roundabout" way.


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## butcher (Dec 12, 2018)

Jovane, 
Sorry but I have to agree with Dr xyz that your trying to pull your horse by jerking on the cart, it is easier to get the horse to pull the cart so you can ride along smoothly.

Study well anything your working on, before buying anything, or doing any experiments, when purchasing chemicals or labware be sure it is what you need, you will also need to understand the dangers involved...

Looks like you have two acids one with sulfuric and one with HCl, did you get the MSDS or safety data sheets for these? Some products contain ingredients which give problems or can contain other chemicals...
I cannot see enough information from your photos to tell what acid or product you have pictured, except that one contains HCL the other H2SO4.

I also see a roll of solder. do you know the composition? lead, tin, copper, silver, antimony... any markings like 60/40 on the solder?

The silvery metal beads in your ( from your friend) could be tin or contain tin as a solder? I do not know.

When tin dissolves in HCl you may not see much of a reaction, with a little heat you may see some bubbles come from the metal, the solution of stannous chloride can be water clear. Other metals like copper can color the solution, silver or lead if involved (solder) will form a white cloud and white precipitate (powder) antimony can leave a bit of black powder insoluble in HCl or the stannous chloride solution.




You seem to think because I mentioned a grout cleaner that anything that cleans grout bought at your store will work, this is not true, sulfamic acid is one chemical used to clean grout, as well as many acids or combination of acids. in my country, one brand of grout cleaner contains almost pure sulfamic acid (a white dry powder).

Research the chemicals before buying them, research before using them, remembering the most important thing is to research the safe usage and the safe disposal...


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## Jovane (Dec 12, 2018)

Thanks Dave...so noted....nicely explained ..... will have to wait till monthend to be in South Africa to sèek all I need...


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## Jovane (Dec 12, 2018)

:? Why does hoke suggest sulphuric acid on page 44 point 5 REMOVING EXCESS NITRIC ACID up to page 45........ I have sulphuric acid..... any comments please. ...


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## FrugalRefiner (Dec 12, 2018)

You have to read the whole explanation.


Hoke said:


> (5) REMOVING EXCESS NITRIC ACID
> You were told to use no more aqua regia than was required. Be-
> ginners always use too much. Experienced workers often do the
> same thing, especially when in a hurry, because fresh acids work
> ...



Dave


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## anachronism (Dec 12, 2018)

What's the chemistry behind sulphuric acid "hastening the expulsion of the Nitric acid?"


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## butcher (Dec 12, 2018)

When evaporating down a solution we begin to vapor off the volatile gases, first vapors composition will be mostly from the more volatiles in solution such as water, water and nitric, and then nitric and HCl then HCl, through evaporation the acids decompose to gases, some metals begin to form insoluble salts (example copper nitrate) which if acidified will later reform nitric acid in solution.

Example: where we can evaporate down aqua regia to a syrup and add HCl and see a cloud of red gas as the copper nitrate reforms nitric acid which decomposes back to NO2 gas, and we evaporate the solution again to rid solution of free nitric...

Added sulfuric can remove all of the nitric and nitrates (and even free HCL if we wished in one evaporation process, where without it we may have to do the traditional (evaporate add HCl, evaporate add HCl and evaporate for the third time to ensure all nitric is gone and all nitrates are converted)...


Sulfuric can help keep base metals from forming nitrate salts, and converting nitrate salts to sulfate salts, by keeping the solution wet during evaporation (sulfuric is not boiling away with other more volatile acids like nitric and then HCl.

Sulfuric will convert base metal nitrate salts to nitric acid and sulfates, where nitric can further decompose and be driven from solution, base metals can form soluble sulfate salts (and insoluble lead sulfate) the hot sulfuric allows you to evaporate the solution down further than you could have without it, and still keep it a wet solution.

We could take the evaporation further using sulfuric than we can from a solution without it, for instance if we evaporated too far by mistake without sulfuric we will be left with a pile of burnt gold chloride and base metals salts, with sulfuric we cannot easily vapor off all of the liquid, but we can practically drive off all of the nitric acids and going even further than is needed we can evaporate off all of the free HCl and still keep the gold in solution...

Adding sulfuric acid changes the azeotrope, of the mixture when distilling or evaporating a solution.


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## Platdigger (Dec 12, 2018)

Ok, sorry Butcher, quote: "we can evaporate off all of the free HCl and still keep the gold in solution..."

Gold in sulfuric...you will have to prove this one to me.
I agree the gold will stay in solution up until most of the hcl is gone but not all.

Have you done this? How do you know all the chlorides were gone?


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## g_axelsson (Dec 13, 2018)

Jovane said:


> Göran...I did mention those crystals are supposedly TIN........Which as far as I understand is also stannous chloride if desolved in HCL.....or am I missing something....
> 
> Jovane..


Yes, tin dissolved in HCl creates stannous chloride. If the crystals shown is tin I have no idea about, to me it's just some metallic objects. To be frank, it doesn't look like tin to me, tin is a low temperature melting soft metal and usually doesn't form nice crystals like that. I would recommend to go with the solder, it will work even if it is lead-tin solder.

Göran


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## arthur kierski (Dec 13, 2018)

i just want to help---i sometimes had problems,with gold solutions where the gold was dificult to precipitate---or because ,i did not denox well,other times because i used excess of smb to drop a few grams of gold--sometimes i used urea,sometimes worked,othe times did not work---but i always knew ,that there was gold in the solutions,because i tested with stanous chloride crystals---strong violet collor(almost black) more gold---weak vilet collor, less gold---no collor,no gold----Fed up with this problem(whem it arises) ,i did the follow: to the solution problem,i added naoh,until hydroxides was formed----i filtrated this hydroxide out,and to it,i added hcl to make a gold chloride solutionn(strong yellow gold chloride solution-----to the solutionn ,i added ,smb,and imeddiatelly ,gold precipitated----the gold at the bottom,and the collor of the solution like water,if the solution continue to be yellow,just add some more smb---and the rest of the gold precipitates---- i did not read all the threads on this topic----but as i said-----i wanted to help friends with the nitric problem in Ar---- regards to all--------------------------------------------------------------------------------------------------------------------------------------------------Arthur Kierski


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## anachronism (Dec 13, 2018)

Platdigger said:


> Ok, sorry Butcher, quote: "we can evaporate off all of the free HCl and still keep the gold in solution..."
> 
> Gold in sulfuric...you will have to prove this one to me.
> I agree the gold will stay in solution up until most of the hcl is gone but not all.
> ...



I do agree with the comment about the free HCl Platdigger. The caveat being "for how long."

If you have made the AuCl bond then you would think that provided there is no mechanism to reduce the gold then there doesn't appear to be a need to be any more free HCl (or more correctly Cl- ions) in solution. The thing is that in reality it's not often that we are dealing with pure gold with no base metal contaminants unless it's a true refine we're carrying out. The base metals interact in all kinds of ways and the bond between the gold and Chlorine doesn't seem to be anywhere near as strong as the bond that's formed between gold and cyanide. This bond is remarkably stable even in the presence of low reactivity base metal ions. Hence the use of zinc rather than copper to "drop" your gold.

That given standard solutions for an AAS are in HCl and they recommend making up your own standards in an weak HCl base.

I'm really interested in the chemistry of the Sulphuric acid namely it's ability to enhance the denoxing process because as it is described by Richard, it explains something to me that I have always wondered about with regards to using Sulphamic acid to denox. 

Thanks for that explanation by the way Richard - it was good reading.


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## Jovane (Dec 13, 2018)

Thanks Auther...making notes as much ss I can.....my one solution dropped gold well...but I'm going to leave it as is till I can do stanous test...battling to get material (tin) or /and stanous chloride here in Mozambique. .....will report on outcome.....


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## g_axelsson (Dec 16, 2018)

Tin is not hard to find. Solder for electronics, maybe a radio or tv shop has it, any garage that repairs cars.... you only needs a few grams.

If everything else fails, find some old electronic gear and take the solder from the circuit boards. It will take some time but it works.

Göran


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## butcher (Dec 16, 2018)

How to check to see if you have made stannous chloride SnCl2, we can use another handy test solution of gold chloride.


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## Jovane (Dec 17, 2018)

Butcher. ..elaborate please. ....


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## FrugalRefiner (Dec 17, 2018)

Everyone should always keep a small amount of a solution known to contain gold. It's often referred to as a standard gold solution. A simple version can be made by dissolving a few gold foils from some fingers. When you make some stannous chloride, you test it by combining a drop of the stannous solution with a drop of the gold solution. You should get a positive result. Once you do, keep the gold solution to test future stannous solutions, which do go bad after time. If your stannous seems to stop working as expected, test it against the gold solution again. If it gives a positive result, you know your stannous solution is still good. If it doesn't, you know it's time to make fresh stannous solution.

Dave


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## Jovane (Dec 18, 2018)

Thanks Dave.....I was planing to get a standard made up as soon as I can get my stanous chloride test solution sorted.....


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## ssendam (Dec 21, 2018)

Hello guys,
I'm not sure if these is the right spot for my question. I bought yesterday aqua regia from a german firm and guess what. It is bright blue. How is that possible? Is this a scam or it can turn blue if the nitric acid is fully saturated?


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## FrugalRefiner (Dec 21, 2018)

Since aqua regia begins to deteriorate as soon as the HCl and HNO3 are mixed, I would never consider buying premixed aqua regia. Loewen, in his book, suggests that if the AR is dilute, it has a longer shelf life, but diluted AR wouldn't serve as well in refining.

We've also learned that it's best to start with a little more HCl than you expect to need, then add the HNO3 in increments, using only enough to dissolve the metal(s).

A blue color most often indicates copper in solution, though other metals can also cause a blue color.

Dave


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## ssendam (Dec 21, 2018)

Thanks for your answer Dave. But, is it possible that the firm in question to add a color indicator to this solution for preventing?


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## FrugalRefiner (Dec 21, 2018)

I'm afraid that's a question I can't answer. Maybe someone in your region will have some idea.

Dave


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## butcher (Dec 26, 2018)

Aqua regia Cl3H4NO3 (4HCl + HNO3)
This discussion I cannot cover all of the different reactions that can occur with using aqua regia and its reactions with the metals, as reactions are not simple, and conditions can vary widely, base metals, excess acid or oxidizer, reagents involved and inter-reactions with salts and acids all can make things complicated.

This discussion will just cover some of the basics, and still, try and keep it simple, although the true chemistry involved is actually more complex than can be shown here. 

These reactions produce toxic acidic vapors which will corrode the environment around them, form dangerous reactions in your lungs, the toxic solutions need to be treated for hazardous waste properly.

Many dangers can exist from these chemical reactions, anyone working with these acids and metals needs to have a good understanding of the dangers involved, and how to protect himself and others from these dangers, have a good understanding of safe lab practices, and working in the lab, dealing with waste byproducts, an understanding of the chemistry involved, chemistry of metals can have many dangers and can involve explosive reactions…

Without the understanding of the dangers, and the use of safe lab practices, you are not only risking your health but also the health of others, and will destroy things around you, and without this understanding, you will also be lacking in the understanding of how to recover and refine gold.

Aqua regia begins decomposition as soon as the concentrated acids of HCl and HNO3 are mixed, the longer it is mixed before use the less potency the acid is to dissolve metals, storing in a closed vessel can cause the container to burst or explode because of the pressure of the decomposition of these gases.

Decomposition is much more complicated as many reactions can occur, but we can write some of the major reactions in a simple equation (with no metals), 3 moles of Hydrochloric acid mixed with 1 mole of nitric acid combined producing 1 mole of nitrosyl chloride gas and 1 mole of chlorine gas and 1 mole of water.
3HCl + HNO3 --> NOCl + Cl2 + H2O

As this decomposition reaction proceeds the nitric acid is reduced while the hydrochloric acid is oxidized, and as the volatile products of nitrosyl chloride NOCl and chlorine gas Cl2 escapes the aqua regia solution loses its potency to react with metals.
3HCl + HNO3 --> NOCl + Cl2 + H2O

Nitrosyl chloride further decomposes into Nitric oxide gas and chlorine gas.
2NOCl --> 2NO + Cl2

The colorless nitric oxide gas will react with air (oxygen) to form nitrogen dioxide.
2NO + O2 -->2NO2

The red nitrogen dioxide gas reacts with moisture in the air or water (or with the moisture in your lungs) to form nitric acid.
2NO2 + H2O --> HNO2 + HNO3

Nitrous acid only in solution decomposes
2HNO2 --> NO2 + NO + H2O
3NO2 + H2O --> 2HNO3 + NO

Elemental gold has only one electron in its outer shell, does not easily give up its electron or share it with other elements.

Hot concentrated selenic acid is the only pure acid by itself that I know of which can dissolve gold.
2 Au + 6 H2SeO4 → Au2(SeO4)3 + 3 H2SeO3 + 3 H2O

HCl acid or Nitric acid neither acid alone will dissolve gold, but most any combination of these two acids will attack gold.

Chlorine is a gas atom has 7 electrons in its outer shell, which is a good candidate to share the electrons with the golds 1 electron (eight being the magic number for a full outer shell of electrons).
Chlorine gas will attack gold at higher temperatures (150-180 degrees C), but I am getting away from the subject of aqua regia, chlorine gas plays a role in the aqua regia solution, getting back on subject.
2Au + 3Cl2 → 2AuCl3

Gold is not oxidized easily (it will not give up its electron easily), HCl acid alone will not attack gold, HNO3 acid alone will not attack gold, but a combination of these acids will.
Chloroauric acid is an inorganic acid that is widely used in gold refining processes. Gold is one of the least reactive metals, but gold reacts with aqua regia to yield chloroauric acid.
Nitric and hydrochloric acid. Nitric acid is a powerful oxidizing agent, capable of converting small amounts of gold to its ionic form, Au3+. Once this ionic form is present in the solution, the hydrochloric acid provides a source of chlorine anions which react with the gold cations to form tetrachloroaurate(III) anions. As the reaction with hydrochloric acid is an equilibrium reaction favoring the formation of chloroaurate anions (AuCl4-), the gold ions are removed from solution making room for more oxidation to occur. And as the solution is so acidic, the chloroaurate anions are swiftly protonated to form chloroauric acid. 
Au + 3NO3 + 6H+ --> Au3+ + 3NO2 + 3H2O
or
Au + 4H+ + NO3- <--> Au+3 + NO + 2H2O (reaction soon moves back to the left)
Then 
Au3+ + 3NOCl + 3NO3 --> AuCl3 + 6NO2

or excess nitric
Au + 6H+ + 3NO3- <--> Au+3 + 3NO2 + 3H2O
Then Au3+ + 4Cl- --> AuCl4

Reaction with gold alone
Au + HNO3 + 4 HCl → HAuCl4 + NO + 2 H2O

with excess nitric:
Au + 3 HNO3 + 4 HCl --> AuCl4− + 3 NO2- + H3O+ + 2 H2O

more excess acids...
2Au + 9HCl + 3HNO3 --> 2AuCL3 + 3NOCl + 6H2O


Chloroauric acid shows acidic behavior by releasing proton in solution. It is a strong monoprotic conjugate acid.
Gold is oxidized by halogens; so, a solution of HAuCl4 can be obtained by the action of chlorine or chlorine water on metallic gold in hydrochloric acid.
2Au + 3Cl2 →2 AuCl3
2 Au + 3 Cl2 + 2 HCl → 2 HAuCl4

The gold-chlorine bond is a coordinate covalent bond, where the electron density is shared but the electrons that are shared both come from the same atom. In this case, the chlorine, which donates its electrons through the mostly filled p orbitals. 

So far, we have not discussed other metals besides gold.

Silver in the gold alloy can form a passivated coating in aqua regia of silver chloride keeping the gold from dissolving in the acid, we in-quarter the gold (25 parts Au/75 parts Ag), and part the gold and silver in nitric acid before processing the washed gold in aqua regia…

Very little silver will dissolve in aqua regia, it will form insoluble silver chloride AgCl very small amounts of silver will go into a concentrated chloride solution with a higher oxidation state AgCl2 which precipitates from diluted solutions as AgCl, the passivated coating can keep gold from dissolving in aqua regia...
It is hard to explain all of the different roles base metals can play in these reactions, with almost all of these reactions being undesirable, they not only complicate the chemistry but interfere with the total process…

Base metals with gold also go through many reactions, several of these metals will make salts of the acids, which when concentrated and re-acidified can reform acids of their salts, complicating the removal of excess acids and of deNOxing of the solutions, the purity of the gold or the ability to recover the gold easily from solution...

Aqua regia is a good refining process, where base metals are very limited, more base metals = more problems.

Aqua regia makes a bad choice as a recovery method…

Mixing HCl and HNO3 to dissolve gold, for example, using 3 parts HCl and 1-part HNO3 is a waste of acids, and can give problems with using excess acids, and trouble recovering gold or reducing gold with excess oxidizing agents…

Using Excess HCl causes no harm, adding very small additions of nitric acid and letting reaction settle down then adding heat, using only small controlled increments of nitric additions we can dissolve the gold consuming the excess nitric as we work.

For calculating how much acids, I normally figure around 3.8ml HCl and 0.95ml HNO3 per gram of gold (the nitric acid added in increments, with heat as reaction slows).

Or around 118ml HCl and 29.5ml HNO3 (small additions as needed) per ounce of gold.
Adding HCl in excess and using nitric as needed, we may not need to use all of the nitric that we have calculated.

Excess oxidizer in this case nitric acid, chlorine, nitrosyl chloride, NO2, (NO3)2 …will keep gold in solution, they interfere with reduction of the gold and can even keep the stannous chloride test from working. 

Oxidizer removal
Base metals involved in the solution can play a very big role in the chemistry, and can even complicate the removal of the oxidizers which keep gold dissolved, or dissolve it back into solution…

The reactions below are mostly just to show examples of some reactions of base metals, (not necessarily what we are dealing with here, but some of which can be involved, and are included as food for thought.

Base metals can form salts of an acid or concentrate upon evaporation then upon addition of an acid these salts can reform an acid of that salt (similar reaction after concentrating the gold chloride solution to syrup and adding HCl to wet, where we see a red cloud of NOx gases, from the decomposition of the nitrates to nitric acid and them NOx formed from the reaction of the HCl on the nitrate salt...

Reactions below included mostly just for added thought…
AgCl + Cl- --> AgCl2
AgCl2 + H2O --> AgCl + Cl-
Ag(NO3)2 + NOCl --> AgCl2 + NO2
AgNO3 + CuCl2 --> 2AgCl + Cu(NO3)2
Pb(NO3)2 + CuCl2 --> PbCl2 + Cu(NO3)2
PbCl2 + H2SO4 --> PbSO4 + 2HCl
Cu(NO3)2 + HCl --> CuCl2 + 2HNO3
CuCl2 + H2SO4 --> CuSO4 + 2HCl
CuCl2 + SO2 + 2H2O --> 2CuCl + H2SO4 + 2HCl
Cu(NO3)2 + H2SO4 --> CuSO4 + 2HNO3

Evaporation
This is used heating solution below its boiling point, a steam bath is useful for controlling the heat…
Boiling would cause loss of gold, evaporation will not if you are careful with the process.

If we just look at aqua regia alone, it begins to decompose as soon as the two acids are mixed, with volatile gases reacting and escaping the acidic water solution, the heat of evaporation would speed up these reactions, and concentrate the solution.

Note here without metals being involved, or excess acids being involved we could theoretically evaporate aqua regia to toxic vapors and steam easily.

More base metals more reactions, more trouble, impure gold…

Excessive nitric acid uses = more trouble.

With gold only in solution (no other base metals), the evaporation process would be simpler than with base metals involved, Gold will not react as much and make the same (nitrate) salts that base metals will upon evaporation, these base metal salts can reform oxidizers when reacidified, leading to more evaporations and reacidifications being needed to decompose these salts to gases and De-NOx the solution…

During evaporation acids concentrate in solution, water, and the very volatile gases come off first, base metals can form salts with the acid, after most of the water has evaporated the concentrated nitric begins decomposition and to evaporate as NOx gases with the water vapors, HCl is less volatile but will also come off as gases, (Excess HCl is no problem and can be beneficial), as mentioned above we can be left with base metal salts in an acidic syrup, adding a little HCl can convert nitrates to nitric which can begin decomposition to NOx gases, water involved in the HCl acid can be evaporated out again , and a little HCl to help remove more nitric or its byproducts, repeating three times is normally sufficient…

By limiting Nitric acid use we can help to reduce the problems of getting rid of it and its products…
By limiting base metals, we also limit some of the troubles…

Sulfuric acid can be beneficial during the evaporation process, the sulfuric acid is not as volatile as the water, nitric and HCl, and will help to break the azeotrope of the more volatile acids (making it more easy to remove the free nitric acid), and keep from evaporating the solution to dryness, and for its benefit in removing lead from the solution…

As The solution gets concentrated and any free nitric acid reaches its azeotrope the acid can begin to decompose fairly violently all at once, I am fairly sure base metal reactions also play a big role in the increase of this feverish rush of decomposed gases and nitric acid in the red cloud to try and escape the vessel.

We must also take precautions to prevent Boil overs of solutions as the reaction goes through this stage.
By watching the concentrated solution --we can see small bubbles forming around the rim of the acid, lowering heat at this point so gases can escape much slower (and we are not driving the chemical reactions so hard, we can get past this point of a (possible boil over), and then regain the heat of evaporation after getting past this critical stage…

After the evaporation process of deNOxing the gold chloride solution is increased in volume with water and normally left overnight to settle out insoluble chlorides like silver chloride, and other insoluble salts like PbSO4…


Urea
Urea and nitric are a dangerous combination.
Urea will not destroy nitric acid,
Although It can remove some of the byproducts or NOx gases from a nitric acid solution.
But considering the dangers and it not really being effective with excess nitric. 
I do not even care to discuss it or use it in the processes.

Gold to consume oxidizers and use up acids
Adding gold to consume free acids this with the heat and evaporation is an excellent choice.
This goes along with the lines of adding gold to excess HCl and nitric only in tiny increments, with heating and concentrating along the process and leaving just a little gold undissolved after the DeNOxing process.

Sulfamic acid H3NSO3
Nitrous acid and sulfamic acid --> products of sulfuric acid, water, and nitrogen gas.
HNO2 + H3NSO3 --> H2SO4 + N2 + H2O
Nitric acid and sulfamic acid --> sulfuric acid water and nitrous oxide gas.
HNO3 + H3NSO3 --> H2SO4 + N2O + H2O

I like to use a combination of these methods, added gold in the reaction, limiting excess nitric, controlled evaporation and the sulfamic acid…

Excess reagent (low oxidizer in solution)
If Most all of the nitric is consumed in the reaction of the solution and only a little of the oxidizers are left sometimes an excess reducing agent like SMB can complete the de-NOxing through reaction with the acids and base metals…

Testing for gold in solution
We can test for gold in solution by reducing the gold to metal and observing a color change.
In the stannous chloride test, the gold is reduced to a metal colloid held in solution by static charges, giving the solution a violet color, in the ferrous sulfate test the gold is reduced from solution to the metal on a crystal of the iron salt leaving a brown colored spot in the test.

In both of these reactions, the gold is reduced to metal in the test, excessive nitric or oxidizers can keep the gold from being reduced or re-dissolve the gold again in the reaction, the test needs to have the oxidizer or free nitric removed before this test will work.
SnCl2
2AuCl3 + 3SnCl2 --> 2Au (colloid) + SnCl4 (purple of Cassius)
Au violet
Ag white
Pt orange
Pd deep yellow to blue-green

FeSO4
3FeSO4 + AuCl3 --> Au + FeCl3 + Fe2(SO4)3 (brown-elemental gold)
In a spot plate several drops of solution to be tested and a crystal of copperas, the gold precipitates from solution as a brown ring of gold, the remaining solution can be moved to the next well in the spot plate (or a Q-tip or paper) and tested for other metals with SnCl2
There are several other reagents or tests like:
DMG used to test for Pd yellow.

Iron in solution can have several colors depending on the oxidation state, from green, brown, yellow or reddish rusty, which can resemble gold or platinum in solution, we can also test for iron:
Ammonium thiocyanate gives a blood red reaction with iron in solution in the spot plate exposed to air.
Potassium ferrocyanide gives intense (Prussian) blue with iron solution exposed to air.

We should also have a known gold solution, to test the reduction potential of our stannous chloride reagent.



Aqua regia is not the only thing strong enough to dissolve gold and form a gold chloride solution.
HCl and NaClO sodium hypochlorite (household bleach) will also dissolve gold fine gold or powders and form gold chloride
Au + 4HCl + NaClO --> HAuCl4 + NaCl + H3O

HCl and 30% H2O2 Hydrogen peroxide will also dissolve fine gold (powders) to form gold chloride
2Au + 3H2O2 + 8HCl --> 2HAuCl4 +6H2O

Hydrochloric acid in the presence of oxidants such as nitric acid, H2O2, NaClO, nitrate salts, oxygen, cupric or ferric ions, and manganese dioxide can dissolve gold.
There are other oxidizers that will work.

There are even salts that when fused with gold can make the gold water soluble when the fusion is dissolved into water.

There are many reducing agents that can reduce ionic gold into the metal, such as: SMB (sodium metabisulfite), sodium sulfite, copperas (Iron II Sulfate), Sulfur dioxide gas (SO2), Sulfurous acid, metals like copper and zinc, oxalic acid, sodium nitrite, H2O2, and many more. 
Sulfur dioxide gas
AuCl4 + SO2 + H2O --> AuCl2 + H2SO4 + 2HCl
Then AuCl2 + SO2 + 2H2O --> Au + H2SO4 + 2HCl
2AuCl4 + 3SO2 + 6H2O --> 2Au + 3H2SO4 + 6HCl


Sodium sulfite
3Na2SO3 + 6HCl --> 6NaCl + 3H2O + SO2
3Na2SO3 + 2AuCl3 +H2O --> 2Au + 2H2SO4 + 6HCl

SMB Na2S2O5 sodium metabisulfite
Na2S2O5 + H2O --> 2NaHSO3
2HAuCl4 + 3NaHSO3 + H2O --> 3NaHSO4 + 8HCl + 2Au

Sodium bisulfite 
NaHSO3 + HCl --> NaCl + H2O + SO2

Sulfurous acid H2SO3 
2AuCl3 + 3H2SO3 + 3H2O --> 2Au + 3H2SO4 + 6HCl


Copperas FeSO4 ferrous sulfate 
3FeSO4 + AuCl3 --> Au + FeCl3 + Fe2(SO4)3
HAuCl4 + 3FeSO4 --> Au + Fe2(SO4)3 + FeCl3 + HCl
2AuCl3 + 6FeSO4 --> 2Au + 2Fe2(SO4)3 + Fe2Cl6

Gold precipitation with Hydrogen Peroxide
(2)AuCl4[-] + (3)H2O2 + (6)OH[-] --> (2)Au + (8)Cl[-] + (6)H2O + (3)O2

Hydrazine
4AuCl3 + 3N2H4 --> 4Au + 12HCl + 3N2

Oxalic acid 
2AuCl3 + 3H2C2O4 --> 2Au + 6HCl + 6CO2

2 HNO3 + 8 HCl + 4 SnCl2 → 5 H2O + 4 SnCl4 + N2O

2AuCl3 + 3SnCl2 --> 2Au (colloid) + SnCl4

SnCl2 (aq) + 2 FeCl3 (aq) → SnCl4 (aq) + 2 FeCl2 (aq)
It also reduces copper(II) to copper(I).
SnCl2 + 2CuCl2 --> 2CuCl + SnCl4 
Tin(II) chloride also finds wide use as a reducing agent. This is seen in its use for silvering mirrors, where silver metal is deposited on the glass:
Sn2+ (aq) + 2 Ag+ → Sn4+ (aq) + 2 Ag (s)

In HCl solution, either metallic Fe or metallic Al will reduce Sn(IV) to Sn(II)
Fe(s)+[SnCl6]2−(aq) ⟶Fe2+(aq)+[SnCl4]2−(aq)+2Cl−(aq)




Reactions for thought:

HNO3 + 3 HCl → Cl2 + 2 H2O + NOCl
HNO2 + HCl → H2O + NOCl
Cl2 + 2 NO → 2NOCl
NO2Cl + NO --> NOCl + HCl
HCl + NOHSO4 → H2SO4 + NOCl
HNO2 + H2SO4 → NOHSO4 + H2O

Cl2 + H2O	⇌ HOCl + H+ + Cl−
The presence of light or oxides of metals like copper can accelerate the decomposition of chlorine and water to HCl
2 Cl2 + 2 H2O → 4 HCl + O2
HClO + HCl → H2O + Cl2
2 NO + O2 → 2 NO2
2 HNO3 → N2O5 + H2O
2 N2O5 → 4 NO2 + O2

2 NO2 <--> N2O4
2 NO2 -->2NO + O2
2 NO2 (N2O4) + H2O --> HNO2 + HNO3
4 HNO3 --> 4 NO2 + 2 H2O + O2
2NO --> N2O2
2NO + Cl2 --> 2NOCl 
N2O2 + Cl2 --> 2NOCl
NOCl + NO2 --> NO2Cl + NO


View attachment Atom_Au.rtf


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## FrugalRefiner (Dec 26, 2018)

Wow! :G 

Dave


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## Jovane (Dec 28, 2018)

Great explanations Butcher....learning more by the day.....God bless...


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## 4metals (Dec 28, 2018)

Can someone explain the trick to opening a rich text format document as the one linked in Butchers post above?


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## FrugalRefiner (Dec 28, 2018)

I just clicked on it and it opened (well, I do have to click the Open button on the dialog box that pops up at the bottom of the screen). I use Open Office, a free suite of applications like Microsoft Office.

Dave


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## 4metals (Dec 28, 2018)

Hmmmmm. I'm a Mac guy and it opens to a mostly blank page that only says "Gold.colloid"


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## Shark (Dec 28, 2018)

I use Open Office and it opens in Open Writer. It originally opens with older versions of Microsoft Word.


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## Shark (Dec 28, 2018)

Here it is in PDF format. Let me know if this doesn't work.

View attachment Atom_Au.pdf


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## butcher (Dec 28, 2018)

It is just the Bohr models for the gold and chlorine atom. and one with a colloid and its charges which can repel others in solution...


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## Radu (Jan 16, 2019)

Hello guys, 

I have some problems related to gold precipitation. I used a poorman's AR (household chemicals with 10 to 15% HCL and bleach), the gold foils a have extracted from many parts were disolved into solution. After this, I tried to precipitate the gold with SMB but not effect. The solution started turning brown but not dark. I poured like half a spoon within 4 hours From last night. It's been 10 hours and the solution is still brown but no dark powder. What went wrong?


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## Radu (Jan 16, 2019)

how long does it take in proper conditions for the gold dust to precipitate? 12 to 24 hours or faster?


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## butcher (Jan 16, 2019)

Chlorine gas generated from the bleach and the hydrochloric acid can keep the gold dissolved.

By Heating the solution will drive the chlorine gas from solution if concentrated very much you may see sodium chloride starting to come out from a saturated solution (HCl acid and the caustic bleach makes a lot of sodium chloride in the process).


Give the solution some heat (do not boil) and try again.


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## ssendam (Jan 16, 2019)

Thanks,

I'll come back with some updates


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## ssendam (Jan 16, 2019)

The solution has some white deposits on the bottom. after 20 hours. I started heating ..hope for some precipitation.


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## anachronism (Jan 16, 2019)

Just for clarity- HCL/bleach is NOT poor man's AR.

If you have white deposits on the bottom- add some water. It's probably salt. 

Have you tested for gold?


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## ssendam (Jan 16, 2019)

I have like 2 mm of white deposits after putting some flame. not boiling. bust still no answer. the solution is brown but at the bottom no dark brown deposits..only white. I do not have any testing solution for gold. All I know is that I have there 25 cell phones 2 printers with cartiges, 3 motherboards, some phone sims and still no answer..Gold was dissolved in solution, was filtered and now nothing when I pour sodium metabisulfite. I have 1 l of solution to process. Tomorrow I'll upload some images.


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## ssendam (Jan 17, 2019)

How can I repair this? :|


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## anachronism (Jan 17, 2019)

ssendam said:


> I have like 2 mm of white deposits after putting some flame. not boiling. bust still no answer. the solution is brown but at the bottom no dark brown deposits..only white. I do not have any testing solution for gold. All I know is that I have there 25 cell phones 2 printers with cartiges, 3 motherboards, some phone sims and still no answer..Gold was dissolved in solution, was filtered and now nothing when I pour sodium metabisulfite. I have 1 l of solution to process. Tomorrow I'll upload some images.



HCl plus tin = stannous chloride- go search "stannous" on the forum and you'll find out what you need to know.

You cannot do this without test solution. With no data you're just guessing and noone can give you proper help. Put it to one side safely and get kitted up with a test solution once you've done your homework. 

Jon


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## butcher (Apr 16, 2019)

Done a little more work looking into this subject.

View attachment Auproject 2.rtf



-------------------------------------------------------------------------------------------------------------------------------------------------
From Miss Hoke and my good friend Harold, we see that approximately one fluid ounce (approx. 30ml) of HNO3 and about 4 fluid ounces of HCl (approx. 120ml) will dissolve a troy ounce of gold.
or approximately 3.8ml HCl and 0.95ml HNO3 per gram of gold.
So, for a mole of gold (197g) or 6.33 troy ounces we can figure:
6.33 x 30ml = 190ml HNO3
6,33 x 120ml = 760ml HCl
from this, we see it takes about one liter(1000ml) of aqua regia to dissolve about 6.33 troy ounces of gold or One Mole of Gold.

mole of gold
some more facts about gold:
gold atomic weight 196.96654grams per mole (approx. 6.33 troy oz)
per mole of gold we have 602,204,500,000,000,000,000,000 Gold Atoms
1 mole 6,022054 x 10 ^23 atoms / 196.97g
the mass of one gold atom approximately 
O.000,000,000,000,000,000,000,327 grams
The gold atom has one electron in its outer shell and 79 protons 79 electrons and 118 neutrons.
the density of gold 19.3g/cubic centimeter 
melting point 1064 degrees C (1948 deg F)

Our blood has about 2 mg of gold
A ball of gold about the size of a tennis ball would weigh about 5.7 pounds of gold.
sea water 2-64 parts per billion of gold
Aurophobia or the fear of gold
AuCl3 solubility 68g/100ml H2O @ room temp.
HAuCl4 solubility 350g/100ml @ room temp.

------------------------------------------------------------------------------------------
looking more into Hoke’s and the formula
I notice that the normally used formulas of one mole of gold + one mole of HNO3 + 3mole or 4 moles of HCl, do not work out…

One mole of gold Au = 196.96655g per mole (6.33 Troy oz)
one mole of gold @ 196.97g /31.103 g per T oz = 6.3328 troy ounces of gold

-------
HCl 37% acid 
Molarity 12mol/liter (12 moles per 1000ml of solution)
Density 1.18g/ml
[3mole solution = ~250ml solution]
[4moles of solution = ~ 333ml solution]
1000ml/12mole = 83.33 ml per mole of HCl
-----------
HNO3 70%
molarity 15.8 mol/liter (15.8mol/1000ml)
density 1.42g/ml
1000ml/15.8 mol per liter = about 63.29 ml per mole of HNO3
-----------

one mole of gold 196.96 grams or about 6.33 troy ounces
Using Hoke’s, we will use about:
3.8 ml of HCl and 0.95ml of HNO3 per gram of gold, so here we will use:
197g Au X 3.8ml/g HCl = 748.6ml HCl
749ml HCl /83.33ml per mole of HCl is about 9 moles of HCL acid
and
from Hoke's about 0.95ml of HNO3 per gram of gold
197g X 0.95ml per gram = 187.15ml of nitric acid 
or about
187.15 / 63.29 ml per mole HNO3 = about 2.96 moles of HNO3 (3 moles)

---
So, our formula for dissolving one mole of gold using Hoke's 
one mole of gold Au (197g) + 9 moles of HCl (748.6ml) + 3 moles of nitric acid (187.15ml) HNO3


My best guess or attempt to represent more closely to Hokes formula 
Au + 3 HNO3 + 9 HCl = HauCl4 + 3 NOCl + 3 H3O + 2 HCl
reactants:
Au (196.97g) + 3moles HNO3 (187ml) + 9 moles HCl (749.97ml)
(about 187ml + 749ml = 936ml of aqua regia solution)
products:
One mole HAuCl4 (411.85g/mole)
3 moles of NOCl (3 x 65.45g/mole = 196.35g)
3 moles of H3O (3 x 19.02 = 57.06g)
2moles unreacted HCl (2 x 36.46 = 72.92g)

So with about 6.33grams of dissolved gold in about 936ml of this reacted acidic (aqua regia) solution.
(solubility of HAuCl4 approximately 350g/100ml H2O)

Here we have to remove the products of nitric acid or nitrosyl chloride from solution before we can precipitate the gold, also we have a lot of solution around 936ml to evaporate and concentrate with heat to be able to remove the excess water and oxidizer (in this case the nitrosyl chloride) from solution… 

-----------------------------------------------------------------------------------------------
Let’s figure this with the more normally used published formula of :
Au + HNO3 + 4 HCL --> AuCl4 + NO + H3O + H2O

Au (196.97g) + HNO3 (63ml per mole) + 4HCl (333ml) or about (396ml aqua regia)
------------------>>>
AuCl4 (303.325 g/mol) + NO (30g/mole) + H3O (19g/mole) + H2O (18g/mole)
so, if my figures are correct to find how much reagents to dissolve a gram of gold in this formula we see that:
63ml HNO3 solution (one mole) /196.97g Au = 0.319ml of nitric per gram of gold.
and
333ml of HCl solution (4 moles)/ 196.97 Au = 1.69 ml of HCl per gram of gold.

This appears to be a more complete reaction, with fewer oxidizers to deal with after the gold is dissolved, but I am unsure of the conditions to actually get all of the gold to dissolve with these ratio’s

I presume using this formula would either take longer or require more heat and evaporation of the solution, at any rate, I personally use C.M. Hoke’s and Harold’s formula amounts to dissolve gold.

It would be an interesting experiment or trial just to see if we could get all of the gold to dissolve using the conventional formula’s

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## anachronism (Apr 16, 2019)

butcher said:


> Done a little more work looking into this subject.
> 
> 
> ------------------>>>
> ...



Marvellous work Richard. Simply marvellous. I'm sure I've managed to get it below 0.5ml per gramme when dissolving pure gold but I've never run a proper trial. I would imagine you would need to add H2O2 to reduce the NOX and possibly run a system like 4metals ran with a condenser in order to get closer to the theoretical figure. That given I'd suggest that it must be pure gold to achieve it. 

Jon


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## butcher (Apr 16, 2019)

I agree, maybe with a cooling of the solution with H2O2 and waiting long periods of time, or maybe possible refluxing?

True, most all of this was discussed was on pure gold, throw in a slew of base metals, some silver and possibly some PGM's into the mix and the reactions change drastically...


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