Making nitric acid is a bit of a pain for me so what I've been doing is using sulfuric and sodium nitrate to generate nitric in situ.
Per the bold print - sulfuric acid plus sodium nitrate (
or any nitrate salt) makes what is known as PMN (Poor Mans Nitric)
I haven't seen anyone using this technique which makes me wonder if there is some disadvantage or other reason that makes it less popular.
This has been discussed MANY times here on the forum - you just have not used the forum search function - or maybe you just don't know what to search for - so if you didn't know what to search for - now you know - search for poor mans nitric --- you will find all kinds of discussions about PMN
Here is one VERY DETAILED discussion about PMN from back in 2009
https://goldrefiningforum.com/threads/concentrate-nitric-acid.315/
Here is a VERY recent discussion about it
https://goldrefiningforum.com/threads/poor-mans-nitric-vs-nitric-cost.32971/
I personally have never had to make PMN because when I was full time refining for a living I bought my nitric in bulk & got it dirt cheap
That said here is my take away (understanding) when it comes to PMN
The main advantage to PMN is that it is away to get nitric for people that just can't get it at all - or have to pay a VERY high price to get it
Some of the disadvantages
You can make PMN with ANY nitrate salt plus sulfuric acid - the quality of the nitric depends on the quality of the nitrate salt be used to make it
Example; - whether you use a high grade/purity salt (98 - 99%) pure salt - or a low grade salt like garden fertilizer which only contains about 15% of the nitrate salts with the rest of it (85%) being made up of other garbage/fillers
They all (the nitrate salts) produce "by products" that ether end up in your nitric (as dissolved "other" salts) - or precipitate out as solids that need to be filtered out
Examples; - sodium nitrate (as I understand it) results in a nitric acid with a by product
IN the nitric as dissolved sodium sulfate - so you have to freeze it to get the sodium sulfate to crystalize so you can filter it out right after taking it out of the freezer
Calcium nitrate - this will produce a solid precipitate by product of calcium sulfate (gypsum) that needs to be filtered out - gypsum is a VERY FINE precipitate so is hard/slow to filter out & some nitric acid will remain tied up in the gypsum - even with vacuum filtering
https://en.wikipedia.org/wiki/Gypsum
Potassium nitrate - this one I am not entirely sure of - but it produces a by product of potassium sulfate (potash of sulfur) - what I am not sure of is if the potash precipitates out & can therefor be filtered out - or if it stays dissolved in the nitric --- my understanding is that though it is water soluble - in strong acid it precipitates out
https://en.wikipedia.org/wiki/Potassium_sulfate
Also - most all of the nitrate salts have at least "traces" of chlorides in them - which will end up in your PMN (as dissolved chlorine in the PMN) - even if they are high grade/purity nitrate salts (98 - 99% pure) & if they are low grade salts (garden fertilizers) will likely be higher in the chlorides that end up in you nitric
This can/will cause a couple problems when using the nitric - IF (the BIG IF) you don't remove those chlorides first - which are discussed in the threads I provide links to
1) the chlorides in the nitric (if not first removed) make it a poor choice for working with silver as the chloride will cause at least "some" production of silver chloride
2) nitric plus (dissolved) chloride/chlorine = AR --- so if you don't remove the chlorides your nitric will essentially be a "weak" AR (kind of like "reverse" AR - which will dissolve (at least) some gold --- so if for example - you use the PMN to dissolve base metal gold plate pins or fingers (without first removing the chloride/chlorine) you are likely to also dissolve at least some gold while dissolving the base metals
Finally- depending on the grade of the nitrate salt you use &/or how you go about making the PMN is going to depend on the resulting end product strength of the nitric you make - it could be as low as only 20% &
at best - maybe 50% - but don/t count on that one
Kurt
