Unknown reason for NO2 production during aqua regia

[orvi]

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.

Outside of the small ammounts of material, bleach is one of the worst oxidizers to be used in refining. It kills the acid, since it is basic, and it is that dilute, you need to add horrible ammounts, accounting for much more waste to treat, comparing to the other methods. And it add up ton of salt, since brine (from which it was firstly made electrolytically) is still left there. Aside of many stabilizers added to prolong the shelf life. Rising chloride content can cause issues with silver chloride afterwards. But this isn´t major drawback, of course

If you can get hands on 30% peroxide, then do it and use that instead for foils and gold powder.
No added salt, molar weight of H2O2 is only 36, and as it comes 30% concentrated, there is fair ratio of volume vs. oxidizing power. Excess is simply decomposed to chlorine and oxygen. And similarly to bleach, no need to kill excess oxidizer other way than adding SMB till gold is dropped. Maybe the cost is higher than other alternatives, but the ease of use, no hassle afterwards and clean operation are major benefits.

PS: At elevated temperature, ammount of dissolved chlorine in solution is miniscule, and decomposition of bleach in strongly acidic enviroment is very quick. Just take the watchglass from the top of the beaker for few minutes and it is done. Also, SMB will react with dissolved chlorine and reduce it back to chlorides as quickly as dropping gold. This will happen simultaneously, so no need to do it separately. Just use SMB like usual and you will be fine

 

[Alondro]

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

That's why it works for me. I have lab-grade pH test strips, so I can watch and adjust the pH quite easily.

Also, gentle warming speeds up the reaction without decomposing the bleach before the gold is dissolved. As with the pH, the temp must also be controlled well. I usually heat it to 50C for the dissolving step. Then I heat it to 90C while outside in the sunlight for an hour to liberate all excess chlorine. Having a lab hot plate is very useful!

 

[Darkthirty]

There is no Home Depot in Pakistan

The point is if you go randomly looking for chemicals people assume you're making drugs or bombs. If you discover its uses, you can usually find what you need. Pakistan has no pools or tile floors?

 

[VanMarco]

Ok, update.
I put 100mL of HCl and about 8-10mL of HNO3 over the leftover material, and left to simmer/low boil for like 1hr, and red fumes were produced again, the solution is yellowish, and has a whitish, cloudy "something" in suspension. what if i add peroxide instead of nitric? I also suspect HCl leaves the beaker while boiling, with the need to add more hcl. I was reading the replies.

 

[Yggdrasil]

Ok, update.
I put 100mL of HCl and about 8-10mL of HNO3 over the leftover material, and left to simmer/low boil for like 1hr, and red fumes were produced again, the solution is yellowish, and has a whitish, cloudy "something" in suspension. what if i add peroxide instead of nitric? I also suspect HCl leaves the beaker while boiling, with the need to add more hcl. I was reading the replies.

If Nitric don’t work Peroxide won’t work.
As you were told, it is probably just the decomposition of the Nitric.

 

[J.Najam]

Ok, update.
I put 100mL of HCl and about 8-10mL of HNO3 over the leftover material, and left to simmer/low boil for like 1hr, and red fumes were produced again, the solution is yellowish, and has a whitish, cloudy "something" in suspension. what if i add peroxide instead of nitric? I also suspect HCl leaves the beaker while boiling, with the need to add more hcl. I was reading the replies.

He recently uploaded the same. See if you can grasp anything useful to fix your issue.

He gets the solution down to a syrup like you've been trying.

 

[J.Najam]

The point is if you go randomly looking for chemicals people assume you're making drugs or bombs. If you discover its uses, you can usually find what you need. Pakistan has no pools or tile floors?

Of course we do. Ill do a search this upcoming week

 

[Yggdrasil]

Ok, update.
I put 100mL of HCl and about 8-10mL of HNO3 over the leftover material, and left to simmer/low boil for like 1hr, and red fumes were produced again, the solution is yellowish, and has a whitish, cloudy "something" in suspension. what if i add peroxide instead of nitric? I also suspect HCl leaves the beaker while boiling, with the need to add more hcl. I was reading the replies.

My last answer was from my phone, now I see better.
You have added enough Nitric to dissolve between 5-10 grams of Gold.
Don't worry about the HCl there is plenty.
How much material is left?

 

[VanMarco]

My last answer was from my phone, now I see better.
You have added enough Nitric to dissolve between 5-10 grams of Gold.
Don't worry about the HCl there is plenty.
How much material is left?

yes, but, if what left is copper, i added enough nitric to dissolve 2-3g of it.
the volume of what's left is about the volume of 40ml mark on a 500ml beaker. will take a picture.
I will also have a stannous chloride test.

 

[Yggdrasil]

yes, but, if what left is copper, i added enough nitric to dissolve 2-3g of it.
the volume of what's left is about the volume of 40ml mark on a 500ml beaker. will take a picture.
I will also have a stannous chloride test.

Simple deduction would guesstimate that to about 50/50 liquid and solid, so 20ml Solids at, guessing sg 5 gives 100mg.
At best we are talking micro grams of values, likely way less.

 

[VanMarco]

Made a fresh batch of stannous chloride from the anydrous (1g sncl2 on 30mL 33% HCl.
First leach, shows clear gold stain present in solution.
Second Leach i've done yesterday, no gold. I guess I'll filter that and keep it for a future refining.
Thanks!

 

[VanMarco]

I dropped the gold with SMB. I didn't have that much excess nitric at all.
Bad part is, I got... colloidal gold.
the portion that precipitated is definitely more than "just colour the beaker"

 

[Yggdrasil]

I dropped the gold with SMB. I didn't have that much excess nitric at all.
Bad part is, I got... colloidal gold.
the portion that precipitated is definitely more than "just colour the beaker"

How do you know you have collodial Gold?
Do you have a picture?

 

[VanMarco]

never mind, it settled out

 

[VanMarco]

thansk so much. got about 1.5g of gold out of the batch.