Urea and nitric acid form urea nitrate a potential explosive compound.
If you look, you can find misinformation almost anywhere, and those who will follow it.
older methods that may have had some benefit in times past mixed in with better methods or information, that may not be desired or the better approach.
This paper looks like someone studied the subject, copied information they do not understand a field in which they have little or no knowledge of or experience in the field, and wrote a pape to get some kind of grade in school. a paper I would not give it high marks myself and can think of more valuable uses for the paper it is written on.
Just because someone wrote a paper or book on it, or made some kind of video, it does not mean it is correct or very effective or the best route.
Urea does not destroy nitric or help to remove nitrates which with an addition of acid can reform the nitrates back into fresh nitric acid.
Urea is terribly ineffective at denoxing a gold chloride solution, urea does not help to get rid of nitrates, but forms them as urea nitrate, with little benefit and more formation of more salts to deal with, as mentioned problems of foaming over losing your gold...
Adding something you do not need, like more garbage in, something in my opinion that you do not need, or you may not wish to deal with in later parts of your processes of refining your gold or which can cause other problems...
Where using the evaporation techniques as taught in Hoke's book, or using sulfamic acid (which has added benefits of helping to remove lead from your gold as well a doing a good job of removing free nitric acid and not forming urea nitrate or another nitrate in your solution to give you problems later in your process.
Sulfamic acid forms H2SO4 in solution which pulls the lead out as sulfates.
Put your urea on your grass to fertilize the grass, (although it is not the best for your grass either), and get Hoke's book...
