Agua Regia not dropping gold after saturation with smb

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Jovane

Member
Joined
Dec 10, 2018
Messages
23
:oops: 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 attached20181211_094107.jpg
 
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).
 
:D 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?
 
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.
 
: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
 
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.
 
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.
 
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.....
 
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?

:)
 
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.
 
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...
 
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
 
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.......
 
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
 
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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