Unknown reason for NO2 production during aqua regia

[J.Najam]

Ok.
I see that part now.
Sorry about coming on so strong.

I can understand that since you are a moderator, you may have too many questions and concerns to cater to. A suggestion; You're human too, take it easy on yourself

I did a few searches for you.

Wow, thanks for this but yeah as you suggested, I tried finding the alternative names and unfortunately none of them are available locally. Thanks for also going out the way to share where it may be available, but again, I'm from south Asia and this location points somewhere in the EU.

just use plain sense and not overuse the Nitric in the first place.

You're kind of right, this approach makes the most sense. I also seen SREETIPS doing the same. Bearing this in mind.

 

[Yggdrasil]

I can understand that since you are a moderator, you may have too many questions and concerns to cater to. A suggestion; You're human too, take it easy on yourself

Wow, thanks for this but yeah as you suggested, I tried finding the alternative names and unfortunately none of them are available locally. Thanks for also going out the way to share where it may be available, but again, I'm from south Asia and this location points somewhere in the EU.


You're kind of right, this approach makes the most sense. I also seen SREETIPS doing the same. Bearing this in mind.

That is odd since you told me you were from Equador and that is where i posted about suppliers.
Look again.
So where are you?

 

[J.Najam]

you told me you were from Equador

Nope. Definitely must be someone else.

So where are you?

Pakistan

 

[g_axelsson]

Classic denoxing, heat, evaporate down to concentrated solution, add HCl. Repeat until no red smoke appears.

Göran

 

[Yggdrasil]

Nope. Definitely must be someone else.

Pakistan

So why is your IP in Ecuador then?
Edit to add:
I have assumed you were in Ecuador due to your IP address I guess.

 

[orvi]

Late to the show, but I am sorry to inform that reason why you continually see NO2 gas evolution from AR is the very reason why you cannot pre-mix and store AR

AR solutions decompose slowly over time, and this rate of decomposition is dependent on temperature, also on the concentration of the decomposition products in the solution and presence of decomposition catalysts.

AR solutions naturally decompose to produce nitrogen monoxide, nitrosyl chloride and chlorine. That is why AR has amber yellow colour. These gasses are dissolved in it. And when you heat it, they start to escape more quickly, and equilibrium will be re-established by more HNO3 being reduced by HCl to form chlorine etc etc

So, you need to de-nox as all other members suggessted. Aside from sulfamic acid, you can de-nox and simultaneously drop precious metals on copper, This is rather wasteful technique if you have quite excess of nitric, but it is beneficial in creating concentrated values from dilute solutions quantitatively. I used this technique a lot when using AR for refining of pins and other mid-grade brass/bronze plated stuff. Best was to combine both sulfamic and copper. It need higher temperatures for proper onset, as NO and NO2 complexed onto mainly ferrous metals is very difficult to de-nox by sulfamic.

 

[Alondro]

For tiny amounts of gold, primarily thin stuff like bond wires, the HCl-bleach method is the cheapest and easiest method to dissolve and recover the gold. Add an excess of HCl, and just a few mls of bleach. No need for denoxing. After the gold has dissolves, just heat the solution while exposing to sunlight a few hours to rid the solution of excess chlorine, and it's ready to drop the gold with SMB. No additional chemicals required, unless you want to add a few drops of sulfuric acid before dropping the gold, then filtering to catch any lead sulfate and get the gold even more pure.

 

[VanMarco]

Wow, thanks for all the replies. the material left is not much at all, that i can see, sand ( I used a pebble mill to mill the material) silicon dies, and some grey goo. I will make some fresh AR with very little nitric and heat it this stuff and see what happens. for the Ar i filtered already, i don't think there's that much nitric so i will just use the SMB to deal with the excess nitric, as I have quite a bit of smb available on hand.
Also I suspect that the NO2 i kept seeing was due to the fact that I might have gotten impatient with nitric boils prior to AR, and some base metal was left behind, namely some silver.
Before i filtered, i added ice, and upon cooling some white precipitate formed.
Thanks so much, will update.

 

[Darkthirty]

View attachment 56733
Is this information correct? can it be used for the same if Sulfamic isn't available?

Sulfamic acid is used for cleaning grout and mortar off tile flooring and swimming pools. You can get it at Home Depot. If you look for sulfamic acid, most people don't have a clue what you are talking about.

 

[J.Najam]

So why is your IP in Ecuador then?
Edit to add:
I have assumed you were in Ecuador due to your IP address I guess.

Whoa, that's strange..

 

[Yggdrasil]

Sulfamic acid is used for cleaning grout and mortar off tile flooring and swimming pools. You can get it at Home Depot. If you look for sulfamic acid, most people don't have a clue what you are talking about.

There is no Home Depot in Pakistan

 

[J.Najam]

cleaning grout and mortar off tile flooring and swimming pools.

i'll check this out and also other approaches as suggested earlier by Yggdrasil. But in its simplest form, best not to add too much, or even if I do, may use the evaporate nitric - re-add HCL technique.

 

[J.Najam]

For tiny amounts of gold, primarily thin stuff like bond wires, the HCl-bleach method is the cheapest and easiest method to dissolve and recover the gold. Add an excess of HCl, and just a few mls of bleach. No need for denoxing. After the gold has dissolves, just heat the solution while exposing to sunlight a few hours to rid the solution of excess chlorine, and it's ready to drop the gold with SMB. No additional chemicals required, unless you want to add a few drops of sulfuric acid before dropping the gold, then filtering to catch any lead sulfate and get the gold even more pure.

HCl bleach for bond wires? I tried doing it once before coming onto this forum.. It didn't work at all. In fact there are many suggestions here to avoid the same as its very ineffective. Your comment here has me puzzled now

 

[Yggdrasil]

For tiny amounts of gold, primarily thin stuff like bond wires, the HCl-bleach method is the cheapest and easiest method to dissolve and recover the gold. Add an excess of HCl, and just a few mls of bleach. No need for denoxing. After the gold has dissolves, just heat the solution while exposing to sunlight a few hours to rid the solution of excess chlorine, and it's ready to drop the gold with SMB. No additional chemicals required, unless you want to add a few drops of sulfuric acid before dropping the gold, then filtering to catch any lead sulfate and get the gold even more pure.

I think it has been established that foils are ok in HCl/Bleach but bond wires not so much.
Tge Bleach tend to take too much time and neutralizes the acid long before completion.
So for bond wires AR has been recommended, at least for most new members.
There are a lot of things that can be done, if one has full control of the process in a lab.
Many members work out of buckets outside and has little to no control of the parameters involved, including pH.
For them AR is the best solution, not cheapest, but the least involved.

 

[Yggdrasil]

HCl bleach for bond wires? I tried doing it once before coming onto this forum.. It didn't work at all. In fact there are many suggestions here to avoid the same as its very ineffective. Your comment here has me puzzled now

It can be done, but you need a very tight control on the pH, and it takes much longer than AR.

 

[J.Najam]

It can be done, but you need a very tight control on the pH, and it takes much longer than AR.

Great, then I have 30% peroxide on hand. Where can I learn more about this pH control, do we have it here on this forum? I'll see if its a feasible practice

 

[Yggdrasil]

Great, then I have 30% peroxide on hand. Where can I learn more about this pH control, do we have it here on this forum? I'll see if its a feasible practice

Peroxide is not Bleach.
Bleach is Sodium Hypochlorite.
It is kept at a very high pH around 11 so it decompose slower.
Peroxide is much easier, it will not neutralize the acid since it is slightly acidic.
But it is much slower than AR.
Just add some Peroxide to the HCl much the same way as Nitric.
But double the volume.
Wait until the reaction stops and add again.
After it is finished, keep the solution warm for a few hours and the Peroxide should have decomposed.
Drop the Gold as usual.

Edit to add some context.

 

[J.Najam]

After it is finished, keep the solution warm for a few hours and the Peroxide should have decomposed.

The heat evaporation technique can also be applied right? And is it also correct to monitor that the same volume of H202 is evaporated by as much as we added to the solution. for instance 30 ml h202 was added, hence the same amount needs to be evaporated to ensure no peroxide remains

 

[Yggdrasil]

The heat evaporation technique can also be applied right? And is it also correct to monitor that the same volume of H202 is evaporated by as much as we added to the solution. for instance 30 ml h202 was added, hence the same amount needs to be evaporated to ensure no peroxide remains

No, there is no need for evaporation with Peroxide since it is relatively unstable and will decompose relatively easy.
It will not create issues the same way as Nitric so I usually go directly to precipitation as soon as it has cooled.
Add a few drops of Sulfuric and let it cool.
Depending on the material put ice cubes in and dilute to drop Silver Chloride.

 

[J.Najam]

No, there is no need for evaporation with Peroxide since it is relatively unstable and will decompose relatively easy.
It will not create issues the same way as Nitric so I usually go directly to precipitation as soon as it has cooled.
Add a few drops of Sulfuric and let it cool.
Depending on the material put ice cubes in and dilute to drop Silver Chloride.

Much appreciate all your responses sir, will keep all this useful information to carry out my processes in the near future.

Many thanks!