# Degassing AR as an alternative..



## AuMINIMayhem (Jul 29, 2010)

:idea: 


I haven't seen anyone approach this idea from this particular angle, so I'm going to propose this idea... now I figure there's probably a reason it hasn't been addressed, so if anyone knows why or it just hasn't really been explored, let me know.. I'm kinda curious if I'm on to something here..

here's my idea...

Assuming you had a vacuum chamber with some sort of "scrubbing" capabilities to keep the corrosive fumes from destroying the insides of your vacuum pump.. could you degass pregnant AR solution by way of vacuum rather than doing the typical boil off without losing pgm's/precious metals?..

What got me thinking of this is I use a vacuum chamber quite often at work to de-gas epoxies, etc. for a space firm and it's really quite effective at getting gasses out of a solution quickly.

Some of the drawbacks would obviously be:
1) the corrosive gases slowly eating away at the insides of a rather expensive vacuum pump or chamber (if it's metal and not a glass bell jar) by way of going into solution within the pump oil or condensing on the insides of the pump itself as well as any metal connectors, tubing, etc.. 

2) rapid expansion/boil-over.. you would have to run VERY small batches at a time and monitor the chamber for a while as liquids violently "boil" at first as gases saturated within the liquid boil off vigorously in the beginning stages. This can be abated by using a pressure relief valve that you turn to allow a little pressure back in the chamber occasionally (every few seconds) at first until things settle down. This is how we vacuum out our epoxies/adhesives, etc.. it first starts bubbling up, but we slowly allow some air in so that it's still boiling but not going over the edges of the container until it slows down. The time it takes is usually based on the viscosity of the product (thicker solutions boil over less rapidly, but expand like crazy and make a hell of a mess if you don't pay attention, while thinner solutions boil like crazy but also cause an issue with spattering and "atomization" if allowed to go unchecked at first)

To remove ("scrub") the fumes exiting the vacuum chamber and entering the pump, we use a glass trap submerged in a Dewar filled with LN2, which is actually VERY effective at getting anything not gaseous to sublimate... sometimes a "cartridge" of "activated charcoal" has also been placed in line after the Dewar to scrub other particulate/gases... 


Anwyays, just a thought... I'd like to try it eventually, but thought I'd throw it out there in case it's been tried and found ineffective.. 

The advantage is that it can greatly (in theory) decrease time spent getting the nitrogen out of your AR, especially if you have a large batch of it (even though you would have to do it in rather small batches depending on the size of your chamber, containers, etc..)

Cheers! :mrgreen:

note: we usually range from 25 to 29.9 inches of mercury to fully degass our epoxies.. seems to be industry standard.


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## AuMINIMayhem (Jul 29, 2010)

We use a setup similar to this... 

http://www.abbess.com/vac/images-standncarts/degascart2/DSCF0007.JPG

with a cold trap such as this:

http://www.kgw-isotherm.com/images/kf/s29.jpg

suspended in a Dewar of LN2 like this:

http://www.lab-instrument.com/images/product_液氮生物贮存容器-1.JPG


Note: LN2 hazards are not just cryo in nature. As LN2 returns to it's gas state, it rapidly displaces oxygen, which can cause a very real danger of suffocation in closed areas. This is only recommended in a very well ventilated area with an appropriate oxygen sensor near-by... don't even bother dealing with liquid nitrogen unless you have been properly trained in handling cryogenic gases. :!:


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## Harold_V (Jul 29, 2010)

AuMINIMayhem said:


> Assuming you had a vacuum chamber with some sort of "scrubbing" capabilities to keep the corrosive fumes from destroying the insides of your vacuum pump.. could you degass pregnant AR solution by way of vacuum rather than doing the typical boil off without losing pgm's/precious metals?..


Your statement is_ very _troubling. You are conveying the message that gold chloride solutions are in need of boiling, and nothing could be farther from the truth. If you were to read Hoke, you'd take note that the process is not boiling, but *evaporating*, and they should not be confused. 

I'm not convinced that you can eliminate free nitric by that method. That's what you must eliminate---not fumes. Please do understand that I am also not a chemist, so I may not understand the issue as well as those that are. 

Personally, I found the elimination of nitric to be a non-issue. As has been suggested by GSP, careful application of your acids can eliminate the bulk of evaporating needs, although in my case, I chose to evaporate for totally different reasons. What I did worked for me, but I am not promoting my method for anyone else, as their circumstances are likely different from those I faced. 

Having said that, your gold chloride solution should be heated at a temperature below boiling, just hot enough for vapors to escape. If you see any color in the vapors, you're running too hot. 

If, in the process of evaporation, you find you have more nitric to eliminate than you care to evaporate, it's dead easy to add a button of pure gold to the solution, so it can be consumed. If you choose to do so, insure that you have free HCl present. 

If you are discussing a gold solution that was created without the use of nitric, none of my comments apply, needless to say, except for the one about boiling. Please, for your own sake, and that of others do NOT discuss evaporation by making reference to boiling. 

There is little need to complicate the evaporation process. It is very reliable and effective. 

Harold


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## g_axelsson (Jul 29, 2010)

By lowering the pressure you are only lowering the boiling point of the liquid. So in a fact, in a vacuum you are still evaporating your acid. As there are no active heat source the acid will be cooled by the evaporation and it will take a long time.

In the end it will take longer time, cost more energy to pump the vacuum, the water is usually damaging the oil in the vacuum pump and the acid would destroy the metal components in it. You still have the fumes to deal with in both cases.

Yes you can do it but it would be stupid. I have access to multiple vacuum systems but to evaporate my gold solution I use the base of an old coffee maker. It is temperature limited and turns off just above the boiling point of water so I never decompose my gold chloride if it dries up.

A fun experiment to do if you have a vacuum chamber... boil some water until it freezes!

:mrgreen: 

/Göran


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## AuMINIMayhem (Jul 29, 2010)

Thanks guys... like I said, it was more of an experiment in thought than in practice. I knew there had to be a reason it hadn't been tried or discussed, I was just curious why or perhaps there might have been an off-chance "Ah-Hah" moment. **shrug** Personally, I think, let me take that back and say "know" that the equipment would be prohibitively expensive regardless. Not to mention, the extra hazard (both environmental and personal) as well as work. 8) 

good to see you on here Harold... nice to see the originals are still kicking around the forums.. 8) 

*BTW.. I'm not boiling off AuCl it's pregnant AR from Catalytics... so it would be predominantly Pt, Rh and Pd.*


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## lazersteve (Jul 29, 2010)

Part of the function of denoxxing PGM solutions is to replace the NO2 bound to the metals with chlorine, forming chlorides of the metals. I don't think this can be accomplished with decreased pressure alone, but I could be wrong.

Steve


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## AuMINIMayhem (Jul 29, 2010)

Harold_V said:


> AuMINIMayhem said:
> 
> 
> > Please, for your own sake, and that of others do NOT discuss evaporation by making reference to boiling.
> ...




Indeed.. you are quite correct. :mrgreen: 

I was exploring the possibility of "de-gasing" .. under vacuum, I should have clarified that...

Yes, there can be quite a bit of confusion between "evaporation" and "boiling".. 

I should explain the original question that got me thinking about vacuum de-gassing: "what form does the free nitrogen take in solution?" 

Is it a dissolved gas such as the CO2 in carbonated drinks? 

Or, is it in a more complex state that has a lower boiling point than the remainder of the solution which is why you can eliminate it by boiling off free Nitrogen without evaporating the rest of the solution and losing values?... sort of like raising the temperature of a water/alcohol mix enough to evaporate off the alcohol and leave the water with relatively minor loss to the water..

I was (mistakenly) under the assumption it was a dissolved gas due to the fact that if using the urea method to get rid of the free nitrogen, you're waiting for it to not have any sort of "fizz" as an indication of success... 

however, after consulting Hoke's book as well as some other reading, that fizzing is more likely a result of an actual reaction taking place instead of a "gas" being displaced out of solution..

Thanks again!
Derek


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## AuMINIMayhem (Jul 29, 2010)

lazersteve said:


> Part of the function of denoxxing PGM solutions is to replace the NO2 bound to the metals with chlorine, forming chlorides of the metals. I don't think this can be accomplished with decreased pressure alone, but I could be wrong.
> 
> Steve




nope, I don't believe you are wrong... your explanation makes a ton of sense, actually.. 8) 

the chlorine needs to knock that NO2 off the bond... after reading up, the dummied down version I figured out is that it's sort of like precipitation, you're knocking one thing out of solution by introducing something else that is much more happy to be in that bond... (right? now I'm second-guessing my fundamental understanding of what is actually happening... LOL!)

8)


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## Lino1406 (Aug 6, 2010)

Is not degassing, but replacing HNO3 (B.P. 86C) with HCl (amazingly
a gas by itself). It is a result of equilibrium between HCl, H2O, HNO3.
This equilibrium may change in a reduced pressure, although I feel 
not so much.


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## Oz (Aug 6, 2010)

Lino1406 said:


> HCl (amazingly a gas by itself).



I would normally ignore this, but I respect your knowledge. Do you mean like H2O is as gas? If not, could you explain this further.


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## Lino1406 (Aug 6, 2010)

Pure HCl is a gas (B.P. -83.7C). Of course with water
it behaves differently, so enabling the thermodynamic 
equilibrium mentionned.


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## Oz (Aug 6, 2010)

OK, I understand now. Nothing different than if you want your oxygen as a solid, liquid, or gas, only this is a compound. I was thinking in terms of R.T. reagents and you made me wonder. You never get answers to the questions not asked.
Thank you


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## 4metals (Aug 6, 2010)

I have always used vacuum to filter aqua regia solution prior to removing the free nitric acid. Often the jugs full of acid sit with vacuum attached and pulling for some time before they are processed further. When the funnel is removed, often with a Whoosh sound as the vacuum escapes, the solution inside always needs degassing of the NOx even though it is exposed to vacuum similar to what is used to de-gas epoxies.


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## Barren Realms 007 (Aug 6, 2010)

4metals said:


> I have always used vacuum to filter aqua regia solution prior to removing the free nitric acid. Often the jugs full of acid sit with vacuum attached and pulling for some time before they are processed further. When the funnel is removed, often with a Whoosh sound as the vacuum escapes, the solution inside always needs degassing of the NOx even though it is exposed to vacuum similar to what is used to de-gas epoxies.



I feel this answers the question asked earlier about denoxxing the nitric with a vacume. The HCL goes into a gas form before the nitric does thus will not work to denoxx with a vacume.


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## Noxx (Aug 12, 2010)

Decreasing pressure will help evaporating your solution.

If you are evaporating many liters of solution, this could help reduce the total energy cost over the years and save some time.

Harold is right; do not let it boil or use a reflux condenser.

There are vacuum pumps made to resist to acid fumes. Piston pumps made of plastics can do it.


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## Barren Realms 007 (Aug 12, 2010)

Noxx said:


> Decreasing pressure will help evaporating your solution.
> 
> If you are evaporating many liters of solution, this could help reduce the total energy cost over the years and save some time.
> 
> ...



Over the long run you will use more energy pulling a vacume to remove the fluids than you will heating the solution to remove them.


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## Noxx (Aug 12, 2010)

You sure about that ? Heating water takes a lot of energy: 4.18J/g.*K

I know that when it comes to industrial dryers, creating a small vacuum is a good way to save energy (and time!).

You need heating along with a vacuum to save energy. Not only using vacuum...


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## Barren Realms 007 (Aug 12, 2010)

Noxx said:


> You sure about that ? Heating water takes a lot of energy: 4.18J/g.*K
> 
> I know that when it comes to industrial dryers, creating a small vacuum is a good way to save energy.
> 
> You need heating along with a vacuum to save energy. Not only using vacuum...





I am not sure what the figures would work out to. But the last part of your statement would be 100% correct


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## Lou (Aug 14, 2010)

It's called a rotary evaporator, and boy do they work swell, especially for concentrating PGM solutions down before precipitation. 

Google up a Buchi R-215.


Using a diaphragm pump with fluoroelastomers means that you can pump on aqua regia fumes all day long, every day. Great for vacuum filtration too. Or you can cheap out and use an aspirator.


Lou


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## Barren Realms 007 (Aug 14, 2010)

Lou said:


> It's called a rotary evaporator, and boy do they work swell, especially for concentrating PGM solutions down before precipitation.
> 
> Google up a Buchi R-215.
> 
> ...



Nice looking unit.


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## slouma37 (Oct 17, 2010)

lazersteve said:


> Part of the function of denoxxing PGM solutions is to replace the NO2 bound to the metals with chlorine, forming chlorides of the metals. I don't think this can be accomplished with decreased pressure alone, but I could be wrong.
> 
> Steve


Hi Master Steve,
no the denoxing doesen't replace the NO to Cl, this reaction took place before any denoxing, the heat just liberate the free NOx in solution (liberated from the replacment process), to eliminate them definitly.

Pressure Can do the Job very well if we study the Diagram curve of NOx wish reflates the states of gaz, pressure, liquid phases of NOx with it's triple point. We call that "Diagramme d'état des oxydes d'azotes" in french dunno what is in english. but it's related in the first principe of thermodynamic(the enthalpy).

Yes this process can be less troublesome if well done, and the idea is just genius and to be tryed and perfectioned.

Salim


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## Lou (Oct 17, 2010)

Pressure alone can remove all of the nitrogen oxides, but the solution must be strongly acidic (hence the additions of HCl) to break down the normally stable nitrate anion into NOx. Heat and vacuum make it go very quick. It is more useful for the PGMs rather than gold, mainly because you're usually left with a strong aqua regia solution of platinum and the ol' gold button in the flask trick doesn't parallel with platinum, at least not on a commercial timescale.


Lou


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