Not to throw a fly into the ointment but here goes.........
There are some rules that refiners who learned here follow, hopefully, and some that a production refining environment would prove impractical. One of them is urea.
Case and point, the setup the refiner from Egypt is using is a setup made by a refining equipment manufacturer and using it requires different techniques than a refiner using a heated reactor. The thread about the Egyptian refinery is
here.
The tumbler plant does not allow the reaction to be heated and does not make it easy to be exact with the nitric acid additions. Also production stone removal lots do not allow babysitting each beaker and adding nitric dropwise until the reaction is complete. These types of reactions work off a chart that says for X ounces of scrap add Y milliliters of Hydrochloric Acid and Z milliliters of Nitric Acid.
So it is easy to see that there is likely free Nitric Acid at the end of the reaction.
For the production refiner with excess nitric and time is of the essence refining schedules, urea is the route taken. Some equipment, like the tumbler, the operator can determine the best acid ratio to use the least amount of Nitric Acid efficiently but there is still excess.
For beaker stone lots, sulfamic can work well, as can heating, if time allows.
Some years back in a thread on the moderators section of the forum, Chris Owen (Goldsilverpro, RIP) was processing some aircraft stators basically using some reverse aqua regia. High nitric and low Hydrochloric Acid. He was having trouble getting rid of the free nitric so I suggested sulfamic acid, which he loved. Truth be told there was so much nitric in the reverse aqua regia he was using that the answer that worked was a combination of sulfamic and a Rotovap, which I believe Lou suggested.
After that, Chris started recommending sulfamic acid on the open forum. I personally use both but having taught so many refiners how to refine, mostly karat gold scrap, I never choose one over the other.
The production refiners of concentrated gold solutions, my strong suit, never leave solutions sitting long enough for chemical evolution of nitric to re-emerge and have never been an issue.
For my own processing, which I do less and less of these days, I believe what Kurt suggests which is less is better. Don't over use nitric.