# Sodium nitrite to precipitate gold from A.R.



## HAuCl4 (Jul 25, 2010)

What is the exact reaction and by-products, please?. 

They can't be nitric acid and HCL right?. I'm somewhat confused.

Ideas to re-cycle the by-products so there's no liquid waste?.


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## Lino1406 (Jul 25, 2010)

N+3 = N+4 + e-
Au+3 = Au - 3e-
ie, each 3 nitrite nitrogens, reduce
one gold atom, becoming NO2 (gas)


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## Barren Realms 007 (Jul 25, 2010)

You will have waste of some sort, not much way around that. It's how you treat it for disposal that is the main factor.


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## samuel-a (Jul 25, 2010)

Lino1406 said:


> becoming NO2 (gas)



that can be recycled to a weak nitric acid with a proper distillation apparatus :idea:


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## HAuCl4 (Jul 26, 2010)

I have looked hard in the internet, and I still can't find the complete reaction and by-products.


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## Irons (Jul 26, 2010)

NO2+Water= Nitric Acid

Nitric Acid + HCl= AR

Some, if not most of your Gold is going to go right back into solution.


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## HAuCl4 (Jul 26, 2010)

Irons said:


> NO2+Water= Nitric Acid
> 
> Nitric Acid + HCl= AR
> 
> Some, if not most of your Gold is going to go right back into solution.



That's why I'm confused.

Hoke has sodium nitrite in her list of recommended precipitants, but does not explain the reaction. I have tried it in the past, and the gold DROPS out of solution very cleanly. I don't know what's left in the "broth", only that there is no gold.

So: I'm still confused.

edit: 
NaNO2 + HCl → HNO2 + NaCl is what happens first where the excess HCl is converted to table salt. (got this from wikipedia nitrous acid).

I guess the AuCl3 + NaNO2 becomes Au + NaCl + a mixture of nitrous and nitric acid ?. That's my best guess at the moment.


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## HAuCl4 (Jul 26, 2010)

HCl + NaNO2 -> NaCl + HNO2

2 AuCl3 + 6 NaNO2 + 3 H2O -> 2 Au + 6 NaCl + 3 HNO2 + 3 HNO3

This is my best guess at the moment. I'm sure someone will correct me, if inaccurate.

From this, it is clear that the nitric acid can be distilled and recycled, and I don't know about the HNO2.


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## 4metals (Jul 26, 2010)

The HNO2 can be scrubbed in an oxygen environment with water to remake the HNO3. In a production environment by sizing the scrubber and limiting the through put by using sealed reactors a properly sized scrubber will work without instrumental control. Of course you will need a constant flow of O2. 

I would suspect with ORP control you could use a water peroxide scrubber and add peroxide to provide the O2 to create the HNO3, then more conventional scrubbing could be employed. 

In either case the presence of the HCl will contaminate the acid you collect but if you're re-using it as aqua regia it's not an issue.


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## HAuCl4 (Jul 27, 2010)

4metals said:


> The HNO2 can be scrubbed in an oxygen environment with water to remake the HNO3. In a production environment by sizing the scrubber and limiting the through put by using sealed reactors a properly sized scrubber will work without instrumental control. Of course you will need a constant flow of O2.
> 
> I would suspect with ORP control you could use a water peroxide scrubber and add peroxide to provide the O2 to create the HNO3, then more conventional scrubbing could be employed.
> 
> In either case the presence of the HCl will contaminate the acid you collect but if you're re-using it as aqua regia it's not an issue.



Thanks again 4metals!. I was thinking an ozonizer to transform HNO2 to HNO3, but you always come up with a better alternative: An H2O2 scrubber or mixer would work fine I think. These would be batches of by-products, not continuous, I think.

I was thinking last night, that this process, as is, would produce more nitric than it consumes, and it would consume sodium nitrite to produce NaCl.

Then it occurred to me that by alternating precipitants, say sodium nitrite on occassion and SMB (or SO2) on other occassions, HCL could be the waste to be recycled, and it would produce more of that than it consumes for gold digesting, producing NaHSO4 and/or Na2SO4.

NaCl can be used / sold for de-icing roads, but what to do with the other stuff?.

One would still need to be buying sodium nitrite and SO2 / SMB, so the "loop" is not closed. Do you think it can be closed so that there is no waste or surplus of chemicals to be re-sold?.


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## HAuCl4 (Jul 27, 2010)

Also trying to avoid a leach/sodium chlorate cell to process the NaCl... :lol:


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## 4metals (Jul 27, 2010)

I only suggested oxidizing the NO2 because it is generally a difficult fume to scrub and sooner or later it brings the EPA down on you. Reconversion back to reusable HNO3 is a win win deal but it does a key piece of the work for you. The scrubbed product is a gas so it separates itself from the chemical mixture you've created to process the gold. 

Since it conveniently becomes airborne and relatively free from other chemicals the process is simple and the results predictable.

If you want to start recovering the chemistry from the soup left behind it's a whole lot more difficult. It becomes more difficult as more and more different metals are introduced into the mixtures you are recovering the PM's from because you are processing waste and have no control of the input. All of the chemical equations in the world don't mean much when you don't really know what you're starting with. 

I've always refined to make money, I would take the gaseous NO2 because there is a double benefit and it's predictable. I'll leave the metal soup for the waste hauler to deal with, and until he comes to me and says he can't do it, I'll concentrate on where there's money to be made.


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## HAuCl4 (Jul 27, 2010)

4metals said:


> I only suggested oxidizing the NO2 because it is generally a difficult fume to scrub and sooner or later it brings the EPA down on you. Reconversion back to reusable HNO3 is a win win deal but it does a key piece of the work for you. The scrubbed product is a gas so it separates itself from the chemical mixture you've created to process the gold.
> 
> Since it conveniently becomes airborne and relatively free from other chemicals the process is simple and the results predictable.
> 
> ...



Of course you are right and all these extra processes are probably not cost efficient. But since my neurons enjoy a workout...

How about putting a DBC-Sx step in the middle to isolate the base metal soup from the AuCl3 before precipitation?. That would isolate one type of waste from the "good type" of waste (before recycling) and also improve upon the quality of the gold. What do you think?.


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## 4metals (Jul 27, 2010)

If your talking karat scrap or scrap with just basic run of the mill base metals the solvent extraction step would help for sure. But we live in an era in which rare earth metals have been intertwined into the mix, often without our knowing, I do not know how all of the specific rare earth metals react in the extraction, that would have to be determined first.


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## HAuCl4 (Jul 27, 2010)

I think that's all well above my pay grade!. :lol: 

I just wanted the nitric and maybe HCl back and recycled!.  

I was just thinking gold, silver, copper, a little nickel and a little zinc, and a little platinum group maybe, traces of other stuff like lead, tin, etc maybe.

What metals are you talking about exactly?.

I read that DBC was very specific extractant for gold and perhaps a little copper, but maybe my information is incomplete?.


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## 4metals (Jul 27, 2010)

La	Lanthanum	used in High refractive index glass, flint, hydrogen storage, battery- electrode, camera lens

Ce	Cerium	chemical oxidising agent, polishing powder, yellow colors in glass and ceramics, catalyst for Self-cleaning ovens

Pr Praseodymium	Rare-earth magnets, laser, green colors in glass and ceramics

Nd	Neodymium	Rare-earth magnets, laser, violet colors in glass and ceramics, ceramic capacitor

Pm	Promethium	Nuclear batteries

Sm	Samarium	Rare-earth magnets, Laser, neutron capture, maser

Eu	Europium	Red and blue phosphors, laser, mercury-vapor lamp

Gd	Gadolinium	Rare-earth magnets, high refractive index glass or garnets, laser, x-ray tube, computer memory, neutron capture

Tb	Terbium	Green phosphors, laser, fluorescent lamp

Dy	Dysprosium	Rare-earth magnets, laser

Ho	Holmium	Laser

Er	Erbium	Laser, vanadium steel

Tm	Thulium Portable X-ray machine

Yb	Ytterbium	Infrared Laser, chemical reducing agent, High-temperature superconductors 

Then there's Gallium which is used extensively to alloy metals.

All of these metals may or may not behave as we would like, and they would require some rather extensive analytical chemistry to determine their presence. It's bad enough for them to be present on a first go round of refining but to show up because you recycled some reagents would really be annoying.


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## HAuCl4 (Jul 27, 2010)

Very interesting. Thanks again!. Everyday I learn something new!.


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## HAuCl4 (Jul 28, 2010)

Hi again 4metals. Again thinking while sleeping:

Do these "exotic" elements follow any type of electromotive reaction series?. 

Are these elements rare enough that they are worth recovering for $ ?.

How difficult or easy is to install a Sodium Chlorate cell to produce it (Chlorate and/or hypochlorite) from NaCl and electricity?.

I was thinking...how would I refine my gold if the world came to an end and there were only few survivors and no place to go shopping for chemicals?.  

I must find a way to quiet my mind... :lol:


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## SilverNitrate (Jul 28, 2010)

See my big gold drop video on dropping AR gold http://www.youtube.com/watch?v=AfTaHvVaOO8


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## goldsilverpro (Jul 28, 2010)

Silver nitrate,

The video was kinda neat and the music was good. However, you seemed to have skipped over the most important part - actually dropping the gold. The topic of the thread is using sodium nitrite to drop gold. Is that what you used?


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## HAuCl4 (Jul 28, 2010)

GSP: I believe he is putting NOx into the flask...and that is precipitating the gold when it becomes nitrous acid???. Maybe I'm wrong. Not a very clear video.

Otherwise I do not see what the little rubber hose is accomplishing. :?:


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## joem (Jul 28, 2010)

I would love to see the drop too.
Do you have that clip?
joe


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## lazersteve (Jul 28, 2010)

I think the solution in the addition funnel is sodium nitrite and he is dripping it into the pregnant solution.

The pregnant solution appears to be green color to me.

Steve


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## HAuCl4 (Jul 28, 2010)

Kind of stating the obvious, but anyway: No need to expel excess nitric with this procedure. 8)

The HCl will become table salt, so you don't want too much excess in there!.


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## SilverNitrate (Jul 28, 2010)

The sep funnel at the top has NaNO2 and water, The bottom is dissolved AU in AR along with mostly CU (this was dissolved karat jewelry). This must be allowed to drip slowly as it evolves alot of NOx gas. Since there is no (AU NO2) ie Gold Nitrates the gold simply falls out. The copper and many of the other metals does become nitrates (or ions) and stay dissolved which would easily be filtered and rinsed from the gold powder. It is uncertain about the other exotic metals such as rhodium and palladium.


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## SilverNitrate (Jul 29, 2010)

HAuCl4 said:


> Kind of stating the obvious, but anyway: No need to expel excess nitric with this procedure. 8)
> 
> The HCl will become table salt, so you don't want too much excess in there!.


You would have to rid at least most of the excess nitric because that nitrate will oxidize the nitrites releasing much more NOx gas. I generally rid most of the nitric in AR with NaOH. good to keep a sprayer of alcohol handy to rid suds.


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## HAuCl4 (Jul 29, 2010)

The idea/motivation behind my posting was to use a generally acceptable procedure (sodium nitrite is one of the reccomended precipitants in Hoke's book), but with the general intention to save/recover/recycle chemicals as much as possible to reduce waste and hopefully save costs.

As 4metals indicated, all the NOx expelled from the precipitation can be easily scrubbed in water peroxide "scrubber", which can simply be a series of tanks connected by pipes and filled with water peroxide, that is slowly transformed to nitric acid, with concentrations rising from the last tank to the first, and little if any NOx in the exhaust.

If one puts a Sx step before precipitation, one could even recycle the nitric acid in the clean soup after precipitation, and neutralize/discard the "dirty soup" from the base metals after Sx. This seems to me the less wasteful method of operation, with the final products being purified gold, recycled nitric acid, and table salt, and of course whatever base metal chlorides or hidroxides or whatever to be further treated/recovered or sent away for disposal (in a smaller quantity).


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