# Pic of sodium sulfite precipitant



## jsargent (Nov 4, 2008)

Here's a pinch of unwashed but dried precipitant I got from my first attempt using sodium bisulfite. Does it appear to be the right color and appearance? Under 40X magnification one can see it is entirely round yellow beads with a non-metallic appearance. The white flecks are salt crystals from the salt/hcl/monopersulfate leach.


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## SapunovDmitry (Nov 4, 2008)

Was it jewelery or e-scrap?


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## jsargent (Nov 4, 2008)

SapunovDmitry said:


> Was it jewelery or e-scrap?


Neither... it was from a digest of placer sand. Below is a pic of my 500 gallon tank doing it's thing. A little over a ton of sand was being digested.


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## butcher (Nov 4, 2008)

are you sure is not Iron salts?


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## jsargent (Nov 4, 2008)

butcher said:


> are you sure is not Iron salts?


I'm not sure of anything. There is still a lot of iron in solution so it could be iron salts though as I understand it, sodium bisulfite is supposed to be selective for gold. Will SB drop iron as well as gold?


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## Harold_V (Nov 4, 2008)

jsargent said:


> butcher said:
> 
> 
> > are you sure is not Iron salts?
> ...



If you have a question about what you recovered, a simple wash in hot HCl will provide the answer. Gold won't dissolve, and will improve in color. Pure gold recovered by precipitation can be likened to ground cinnamon in appearance, although it may clump up, too. Once well washed, gold generally does form clumps. If it doesn't, it's often a sign of very dirty gold (precipitated from dirty solutions). 

Harold


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## jsargent (Nov 4, 2008)

Harold_V said:


> jsargent said:
> 
> 
> > butcher said:
> ...



Excellent advice Harold. I'll give it the HCL test. I'm curious though... if I precipitated it OUT of an HCL solution at about pH 2.0 in the first place, why would it go back into solution in HCL? Is heat the influencing factor or do I also need to drop the pH way below 2.0 to try to get it to re-dissolve?


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## Lou (Nov 4, 2008)

I don't even know where to start on answering that question, albeit a good one from your perspective!

To me, the color looks way off--yours is distinctly orange. Sulfite isn't particularly selective for gold any more than other reducing agents; there's no truly, 100% effective precipitating or reducing agent--everything has some drag down, what matters is how much you're prepared to accept.

If I were you, I would probably take this precipitate and boil it in water for a few minutes, filter, and then boil in HCl, again filtering after giving it 30 minutes or so. If it is unchanged, then I would cautiously add a few mL of nitric acid, warm and look for any color change (particularly green or blue). At this stage you could check for silver/lead but perhaps it would be just easier to digest the lot in aqua regia: add the corresponding quantity of conc. HCl to your few mL of nitric acid and look for a reaction.

We'll take it from there after you get that far.


By the way, what exactly are you doing with this material? It seems that you are doing this at the moderate/pilot scale so you must know this material is auriferous and have assays in hand. It's interesting to see someone step it up a notch!


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## Harold_V (Nov 4, 2008)

jsargent said:


> I'm curious though... if I precipitated it OUT of an HCL solution at about pH 2.0 in the first place, why would it go back into solution in HCL?


My untrained mind thinks it would be akin to growing crystals. If you present a barren solution, the crystals may re-dissolve, assuming that's what they are. I'm thinking crystals of iron in this case, not gold. I am assuming that your solution bordered on saturation, allowing them to form originally. Considering your ore was placer sand, I expect it was very high in iron. If so, you are seeing one of the many reasons why black sand is not an easy project. 

I've precipitated, literally, ten thousand ounces of gold and have never seen it come down the color you have. I'm not implying it isn't possible-----only that, perhaps, my circumstances didn't present the opportunity. It will be interesting to see what comes from your small batch.



> Is heat the influencing factor or do I also need to drop the pH way below 2.0 to try to get it to re-dissolve?


I'll just have to take a poke at this thing. I expect that heat will accelerate the reaction, but you'd likely achieve the same results even applied cold----it would just take more time. Just like salt or sugar will dissolve in cold water, so too will other substances. It's a matter of time and degree of saturation. 

I learned early on to use heat for all of my reactions. It proved to be the saving grace for me when I found myself so busy with refining that I was at the fume hood for 12 hour, or longer, days. 

As far as pH is concerned, if you apply HCl, it most assuredly will be low, 1 or below, so I don't think that's an issue. 

One thing I'd do is test the solution for gold (stannous chloride or ferrous sulfate) after boiling. 

Harold


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## jsargent (Nov 4, 2008)

Lou said:


> I don't even know where to start on answering that question, albeit a good one from your perspective!
> 
> To me, the color looks way off--yours is distinctly orange. Sulfite isn't particularly selective for gold any more than other reducing agents; there's no truly, 100% effective precipitating or reducing agent--everything has some drag down, what matters is how much you're prepared to accept.
> 
> ...



Thanks for your feedback Lou! I didn't realize sodium bisulfite was no more selective than other precipitants for gold. I have read many sources singing the praises of SB and SMB so I had hoped it would prove ideal for my project. I must say it seemed to drop this, whatever it is, at a comfortably low pH unlike other agents I've tried like sodium borohydride, which creates a horrendous mess by dropping everything but the kitchen sink..

I hesitate to take this precip back into HCL or AR solution at the moment as I'm considering sending it to the assayer for ICP analysis. That'll solve the riddle. I forgot to mention, when I first dried this precip, it was mostly light brown, except for one area which was an odd pink color like palladium looks. I got sloppy and things got mixed together so the color you see is the result.

What I'm trying to do is prove, by a small pilot test extraction on a few tons of ore, that this material has extractable gold values in the neighborhood of what the assays indicate. My first two runs averaged only a 14% recovery but I have identified my technical errors and feel confident my next recovery % will improve.


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## Lou (Nov 5, 2008)

Ah, ok, not exactly the details I was hoping for but, well, I guess I can't blame you.

Well, one more word of advice is to have fire assay done on the concentrates/sands/whatever you are processing. Fire assay will be more realistic on what you could possibly recover. ICP is a dish best served with the PGMs because they don't usually fire assay well (except in special circumstances or protocols).

It's a pity sand is so abrasive and that there's likely a lot of iron present. I would just say grind it up and barrel roll it with bleach+HCl but that would probably be a pain in the behind in your case.

Ever considered gas phase extraction? It doesn't only just work on the PGMs...it's a miracle for many things.


Lou


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## jsargent (Nov 5, 2008)

Yeah the fire assay, when done right, is more definitive. Last time though, the assayer I normally use didn't take into account the very high amounts of chloride in my borohydride precipitate (40-50%) and came back with a non-detect on gold. I'm assuming it all went up in AuCl vapors. An ICP analysis on same precip showed significant gold values. I tend to agree with the ICP based on the several grams of gold I ended up with in my hand after cuppeling my ion exchange residue. From now on if I want a fire assay I'll just put on my Darth Vader lead-vapor protection gear and do it myself. :wink:


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## jsargent (Nov 5, 2008)

Lou said:


> It's a pity sand is so abrasive and that there's likely a lot of iron present. I would just say grind it up and barrel roll it with bleach+HCl but that would probably be a pain in the behind in your case.
> 
> Ever considered gas phase extraction? It doesn't only just work on the PGMs...it's a miracle for many things.
> 
> ...


The procedure I think makes most sense is to separate the black sands first to reduce volume by 95%, then crush to about 200 mesh, then extract iron with citric acid or HCL, then go to the HCL, salt, monopersulfate leach of the slurry in an air agitated cone bottom tank. no pumps to worry with and well... it looks pretty cool. LOL

Now the gas phase process I am not familiar with. I did read of a process of purposely volatizing gold as the chloride and condensing the vapors in a distillation apparatus. Is this what you are referring to?


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## butcher (Nov 6, 2008)

I would roast the black sand (sheet metal on bed of hot coals) for about an hour at greater than 750 degrees F. before any leach process I used. :wink:


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## Oz (Nov 6, 2008)

Watch for the possibility of arsenic with roasting black sands.


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## butcher (Nov 6, 2008)

another thought is go after the iron selectively(main base metal) concentrating gold left, after that then leach for the gold


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## jsargent (Nov 6, 2008)

Good idea Butcher. That's sort of what I'm doing with the citric acid wash, trying to remove as much iron as possible prior to main leach. What method do you have in mind?


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## Shecker (Nov 6, 2008)

I offer this just as a thought. I have found that the right combination of nitrates does a good job of leaching placer material. The objective is to produce an N3 molecule (a triple nitrogen bond). I start with urea which has a double nitrogen bound and then add sodium/potassium/ammonium nitrate.
A littler nitric acid could be added to adjust pH and add extra nitrogen to the reaction. The values can be recovered by cementation on copper. This leaves iron in solution. The gold that is produced by cementation is brown in color (tannish-brown) and any silver and pgm's are metallic.

This is something I am experimenting with and it seems to do an excellent job of leaching and recovering the values. Try it on a beaker scale. It is very easy to scale up.

Randy in Gunnison


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## Lou (Nov 6, 2008)

N3 is the azido function. I don't see how it would have any use to anything we do Randy, mainly because it is a.) extremely unstable, b.) extremely poisonous, c.) almost always explosive. Also, it is only very rarely with a triple bond. Nitrogen itself can't be bonded to two other nitrogens by triple bond, but in a resonance structure, it can be triple bonded to another atom.

[Some of the more astute members will note that N3-, is azide, the very same azide as in lead azide, or sodium azide found in air bags. This is a sensitive primary explosive.]


That handled,

Jsargent,

I would steer clear of borohydride. You have no reason to use it--it is expensive and as you mentioned, quite lacking in selectivity. It is best used with the PGMs, and even then, only in very limited circumstances when you want a special form of the reduced metal.

Sulfites and sulfur dioxide do a fine job for what you're doing. Just expect to have to wash the gold after, then redissolve and precipitate again (perhaps try oxalic in this case).

As for dissolving away the iron and gangue, that could be done but it would be reagent intensive. You could use hot sulfuric acid and dissolve all the iron, filter it out and then boil in caustic to remove most of the silica as a silicate. That should drastically concentrate your gold to the point where you should be able to see it! At the same time, it would border on a net money loss unless your sand was loaded with fine gold particulate. Again, I have no details so I can hardly make a suggestion.


As for the gas phase process, it is well known to those in the field that the PGMs, gold, and quite a few other metals beside (Zr, Ti, Hf, Ta, Nb) can be transported under special conditions. This can be manipulated to obtain metals of exceptional purity and also great economy in removing values from a low concentration system. It's most notable use is in hot wire contact decomposition (indeed it is the van Arkel-de Boer aka crystal bar (iodide) process). Basically, gas phase transport of PGMs is a similar animal, but these are even more thermodynamically unstable and readily fall apart. That can be taken advantage of, but it requires some know-how and specialized equipment. 

Here's an example of some gold and platinum done using this process (or perhaps variation) by a friend of a friend. He also does many other interesting things beside.

http://periodictable.com/Items/078.14/index.html

http://periodictable.com/Items/079.20/index.html

Time permitting and the forum interest accommodating, I will post some of the things _I_ do with this process, granted, on a whole different scale.


Lou


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## lazersteve (Nov 6, 2008)

edit: [This post was typed as Lou was typing his above.. sorry for any duplication of info]

Shecker,

Triple bonding with nitrogen forms nitrides.

Here's the wiki on nitrides:

Nitride

and there metal formations from triple bound nitrogen:

Reactions

I think your terminology is confusing the number of open electron orbitals in the nitrogen bond with the number of filled orbitals. 

Azides are an example of a three double bond nitrogens (N3-):

Azide Structure

and a metal azide compound:


[img::]http://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Sodium_azide.svg/200px-Sodium_azide.svg.png[/img]


The double bond in the Urea molecule is at the carbon-oxygen atom, not the nitrogen as clearly shown below. In fact three of the nitrogen orbitals in urea are already filled.

[img::]http://upload.wikimedia.org/wikipedia/commons/thumb/c/c0/Urea.png/120px-Urea.png[/img]

For the above reasons I feel your analysis of the reaction mechanisms may need to reconsidered. I'm not saying your reaction doesn't yield the results you are getting, merely that your understanding of the mechanisms behind the reaction may be off. You may find that by examining the true mechanisms of the reaction that you can eliminate some of the reactants.

Steve


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## Shecker (Nov 6, 2008)

Very well could be. This is just something I am experimenting with and right the results are pretty good. But it is nothing more than an experiment.

Randy in Gunnison


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## jsargent (Nov 6, 2008)

Good thoughts all... in particular Lou, fascinating info on gas phase/ vapor deposition. Dead on regarding the economics of intensive reagent use. I can get rid of 99% of the iron but at what cost and do I really need to? I just need to eliminate enough of it from the black sands so there is not an overwhelming interference or co-precipitation with the PM's

All of your inputs are much appreciated. This forum has been a blessing.

Bottom line here is being able to develop a protocol that is economical and I feel certain I can do it with help from you gentlemen.


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## butcher (Nov 6, 2008)

just a thought Iron less reactive, disolved in acidic solution, than gold, especially if gold is not oxidized,


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## Lou (Nov 6, 2008)

Butcher,

Iron is indeed less reactive than gold in solution because gold would more gladly be reduced than iron. Please bear in mind, that if gold is dissolved into an acidic solution, it is oxidized, just as the iron is oxidized. This is why sodium metabisulfite or SO2, or other reducing agents selectively (to an extent mind you) reduce gold but not other metals--sulfite just isn't that terribly strong a reducing agent.

Remember, the only time gold or any other precious metal will dissolve but not be in an oxidized form is when it is dissolved into another metal, at high temperature. 

Thanks Steve for spreading information.

Thanks Jsargent for the compliments, I figured you would find it useful. I am of the opinion that gas phase chemistry is and will be of great import to the refining and reclamation industry. I have recently acquired several tube furnaces to pursue this technology. I far prefer it over conventional wet chemistry for many reasons: can be closed system so limited loss, superior first run purities, typically is faster, etc.


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## lazersteve (Nov 6, 2008)

Lou,

I'm with you 100% on the gas phase chemistry over wet chemistry, but my resources don't permit me to pursue the gas phase project just yet.

One day I'll set up a small furnace just to demonstrate it for the forum.

Steve


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## jsargent (Nov 6, 2008)

Lou said:


> Butcher,
> ...I am of the opinion that gas phase chemistry is and will be of great import to the refining and reclamation industry. I have recently acquired several tube furnaces to pursue this technology. I far prefer it over conventional wet chemistry for many reasons: can be closed system so limited loss, superior first run purities, typically is faster, etc.



Now ya done it.. you've gone and got me interested in gas phase extraction. :shock: 
I'm sure my investors will be delighted to hear about yet another bleeding ege technology just waiting for me to sink my teeth and their money into... :!: 
Just guessing here but are you vaporizing your ore or impure metals in a carbon arc in a controlled atmospheric flow then precipitating the vapors selectively somehow or is it done in a vacuum chamber or what? I believe Apollo Diamonds http://www.apollodiamond.com/ is using a vacuum chamber setup to make their ultra high purity stones. Fascinating stuff.


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## Anonymous (Nov 6, 2008)

The gold and platinum, but exspecially the gold crystal, wow,


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## Lou (Nov 6, 2008)

I was thinking about making a few of those gold crystals, if I do, anyone want a few? Of course they'll be 5N+....

Anyway, jsargent, you're free to privately message me about the gas phase. It might be right for you. And yes, you are guessing.

Steve, I really approve of all the good work you do for the forum, and just for the sake of reducing the general ignorance regarding precious metals that abounds on the net. Many people think there is magic to it!

That said, I would be glad to help facilitate your experiments. I have some quartz tubing and other necessary apparatus that could help you out. Talk to me some time about it. I can also perhaps offer some other items again (of course discounted).


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