It would depend on what its mixed with. and it could be complicated.
My experience is in washing cocaine. Trying to get the fake drugs out of it, you soak the powder in a few different chemicals and dry it out in between. I would assume there is a way to pull out the NaNO2 out of even NaCl. Could be complicated and overly expensive. Non-aqueous chemicals are hard to get your hands on and water will ruin it.
Acctually i found this.
i have done this many times and it is relatively simple, the mixture was a 10%sodium nitrite, 90% sodium chloride. I will give an example for a 1kg mixture.
Place mixture into a column and run enough water through the column to dissolve all the sodium nitrite at room temp. This is 1000/815=1222ml, then add 10%, so around 1400ml.
You now have a solution of 1400ml water, 100g NaNO2 and around 350g (x1.4)=490g sodium chloride, its solubility in cold water.
Boil the solution down until the sodium nitrite has reached saturation at 100C, which would be around 100mL, but practically it will be closer to 200ml. At this stage you will have an enormous volume of sodium chloride suspended in the sodium chloride/sodium nitrite/water solution. Hot filter very quickly and at temperature.
Your solution now has ~200ml h20, 100g sodium nitrite and ~50g sodium chloride.
Chill to ~2C, the sodium chloride largely remains in solution the sodium nitrite will crystallize, this filtered gives you about 75g of your original sodium nitrite which can be re-crystallized from Methanol/water to give quite pure sodium nitrite.
The remaining solution should be kept and accumulated and re-concentrated.
When i did this some years back i used 10Kg salt at a time in a long column and was all very manageable. I was rather pleased something i figured out worked reasonably well as designed for once. Exploited is the fact the sodium chlorides solubility remains largely consistent over 100C solution temperature whereas the nitrites solubility doubles.
Good luck!