Nitric Freeing Methods (excluding evaporation)

[huggybear]

Hi all,

This forum has been a valuable resource for me but I have a question which I don't think has been answered in depth.

I have a large volume of gold dissolved in aqua regia and I need to nitric free the solution before dropping out the gold.

I don't have the capability to boil down the solution, due to the quantity and time constraints.

I have seen the urea method recommended by a number of users but I have also read various users saying they don't recommend this method.

If indeed it is the "best" reagent to use, what sort of quantities would I need to "free" a given amount of nitric acid.

I am obtaining this liquor from an external source so I am unable to limit the nitric acid content, meaning unfortunately, there is quite a lot of nitric acid in it.

Thanks in advance for your help,

huggybear

 

[Alondro]

The best is SULFAMIC acid, which will remove the nitrate and generate sulfuric acid and nitrous oxide (N2O) gas... which is the old-timey general anesthetic commonly called 'laughing gas'. So make sure you have seriously good ventilation!

 

[FrugalRefiner]

Another alternative is to dissolve more gold in the solution to exhaust the nitric.

And, yes, the question has been answered innumerable times. Eliminating excess nitric is known as deNO_Xing. When nitric acid decomposes, it creates several gasses composed of Nitrogen and Oxygen, collectively called NO_X (Nitrogen and Oxygen compounds, where the _X represents the ratio, like NO, NO₂, etc.).

Dave

 

[huggybear]

Thanks for the quick responses!

Sorry I forgot to mention that I have read about the gold addition to consume the nitric, as mentioned by Harold and others.

Since I have a lot of nitric in solution, I want to avoid having to use lots of gold to nitric free (because all the gold will require re-refining afterwards).

Ideally I am looking to use a "cheap" reagent to perform this task.

Does anyone else have experience using sulfamic acid? i.e. is it commonly used and safe for this purpose (providing adequate extraction)?

huggybear

 

[eaglekeeper]

It's used for many things.... but you can get Sulfamic acid from a flooring/hardware store as a grout cleaner.

 

[eaglekeeper]

Before I filter my solution I'll add a pinch of sulfamic acid until the fizzing stops...then filter. That way any undissolved sulfamic acid will stay in the filter.

 

[Yggdrasil]

Thanks for the quick responses!

Sorry I forgot to mention that I have read about the gold addition to consume the nitric, as mentioned by Harold and others.

Since I have a lot of nitric in solution, I want to avoid having to use lots of gold to nitric free (because all the gold will require re-refining afterwards).

Ideally I am looking to use a "cheap" reagent to perform this task.

Does anyone else have experience using sulfamic acid? i.e. is it commonly used and safe for this purpose (providing adequate extraction)?

huggybear

This is one if the most covered topics on the forum.
So how you have managed to not find it, I can’t say.
And please use the correct term deNOxing. Nitric free seems like someon is giving away Nitric for free.
The best method of them all is to not add too much Nitric in the first place, which leaves me to the next question.
How did you make your AR in the first place?

 

[huggybear]

This is one if the most covered topics on the forum.
So how you have managed to not find it, I can’t say.
And please use the correct term deNOxing. Nitric free seems like someon is giving away Nitric for free.
The best method of them all is to not add too much Nitric in the first place, which leaves me to the next question.
How did you make your AR in the first place?

Thanks again all,

One last question: once I have dropped out the gold, I plan to use zinc powder to cement the PGMs. Just wanted to double check that the sulfuric acid produced by the sulfamic acid additions won't harm the cementation efficiency.

If you read my original post I said I obtained it from an external source.. it is not me who added the nitric.

Now that I am aware of sulfamic acid and its uses, I can look up some of the older posts. Cheers.

 

[Yggdrasil]

Thanks again all,

One last question: once I have dropped out the gold, I plan to use zinc powder to cement the PGMs. Just wanted to double check that the sulfuric acid produced by the sulfamic acid additions won't harm the cementation efficiency.

If you read my original post I said I obtained it from an external source.. it is not me who added the nitric.

Now that I am aware of sulfamic acid and its uses, I can look up some of the older posts. Cheers.

You said you have a large amount of AR, nothing about the source until at the end of the post.
What is the source of the precious metals in the AR?
In other words, why do you think there are PGMs in there or even if the Gold are in there?
Have you done a stannous test?
Or other tests?

 

[huggybear]

The liquor contains approximately 500ppm of platinum and palladium that I want to cement out once I have dropped the gold.

I've never dealt with sulfuric acid so want to make sure this won't interfere with the PGM recovery.

Thanks

 

[Yggdrasil]

The liquor contains approximately 500ppm of platinum and palladium that I want to cement out once I have dropped the gold.

I've never dealt with sulfuric acid so want to make sure this won't interfere with the PGM recovery.

Thanks

Dilute Sulfuric is of no concern regarding Pt and Pd.
What is the source of the PMs?

 

[huggybear]

Dilute Sulfuric is of no concern regarding Pt and Pd.
What is the source of the PMs?

Ok that's good to know.

I'm not sure what the source is, only the approximate concentration.

Thanks everyone for your help... I'll be back if I run into any issues!

 

[4metals]

The metal of choice for cementation of PGM's is copper, depending what the other metals in solution are, zinc may drop a lot of undesirable metals leaving you with a mess that isn't close to refined. Copper drops only PM's.

That is why you have been asked what the source is, but if you don't want to answer you may have to deal with the mess.

 

[huggybear]

Thanks for the heads up, I will use copper. I assume shavings will be sufficient?

The source of the PGMs is most likely dental scrap but I'm not sure as the material that went into the solution somes from a few different sources.

 

[4metals]

The best is atomized copper very fine mesh, slowly added as to not add excess. If you add copper shavings go slowly adding a few and mixing continuously. If you add too much copper there will be excess copper which will lower the purity. Go slow, mix well, and test with stannous often.

 

[huggybear]

Thanks. Is the build up of hydrogen gas during cementation a hazard given the larger volumes I'm dealing with?

 

[4metals]

If you are working in a hood no problem, if outdoors it should be OK with a slight breeze. Keep your face away and do like Bill Clinton, don't inhale!

 

[huggybear]

Perfect thanks again for your help.

 

[zachy]

but I thought that the sulfuric acid is added and the solution should be boiled, or can it be made cold?

 

[Yggdrasil]

but I thought that the sulfuric acid is added and the solution should be boiled, or can it be made cold?

You don't add Sulfuric, you just add Sulfamic which will turn the Nitric to Sulfuric.
Edit to add:
The solution needs to be hot, around 70-90 Centigrade for it to work properly.