I have never added urea to a silver nitrate solution.
I do not under stand why you guys would do that?
The silver would precipitate just fine without it.
If you had excess nitric it would just dissolve a little more copper to replace the silver.
Or you could add more silver to use up the nitric.
Even better to use only the nitric you need to dissolve silver with heat (leaving some silver for the next batch, or after you have just a tiny amount of silver decant the silver nitrate solution and finish the small amount of silver with fresh dilute HNO3, that way if you use excess on it a little heat can drive it off.
Oneal, it looks to me your blue foam is copper carbonate, from the CO2 gas the urea makes, the copper carbonate and it will not be very soluble, the nitric Kadriver suggests adding may help dissolve it, but to me that is a waste of nitric and urea fertilizer,
I would use the urea on the grass and keep it out of your lab, actually there are some dangerous chemistry compounds that can form when you mix urea and nitric acid, they can also form ammonia in the solution, now you can have another dangerous compound’s with than ammonia and silver mixed with urea nitrate, (I do not know all of the chemistry, as from reading about it can get really complex)(but from what I have read I sure would not want to make up something that would blow my face off or worse) my suggestion get rid of the urea there is no need for it.
Kadriver I notice you keep moving you metals around from one container to another (pouring to decant solutions),
I run almost a whole process in one container like the casserole dish on the hotplate almost from beginning to end, it stays on the hotplate almost the whole process,
Here is example of some type of process I may run:
I may incinerate, wash, decant, dissolve metals in acid like nitric, decant, rinse, decant, dry, incinerate, wash, add another acid like HCL to dissolve metals, decant, rinse, neutralize, decant, rinse, dry, incinerate, rinse,
(Now they may come off the hotplate and out of dish this is the only time the dish came off the hotplate or powder removed from the dish) I may remove powders, and screen them through funnel with Nylon type screen into a jar (large material in funnel may go into a jar to be processed later, or discarded depending what it was),
And then fine metal powder goes back into casserole dish) to finish the process on the hot plate, then I may add an acid to dissolve values, decant solution, rinse, and may still have other values to process in the dish.
Point is it stays in the pot the most of process.
I normally do not pour solutions to decant them, I use a suction bulb (it looks like a large plastic syringe with a green bulb attached (think turkey baster suction bulb) they are very chemical resistant and hold up well to all the acids I use, it takes a little while but I can decant a five gallon bucket with this tool when I want to, (it is also a good tool to start suction on a cipher hoses with), another tool I use to decant with is the plastic pipette, you can get down to the last drop without picking up powders,(a trick I use is cut the bulb off a pipette and stick its tube onto my larger suction bulb, now I can reach further down a jar, and have a small opening on the end to control how fast the liquid suck out (so as not to move liquid in jar to disturb things, or get larger volume than pipette could alone or reach the last drop way down in the bottom of jar.
Some other handy tools in my lab, fiberglass stirring rod, glass stir rod, long handle plastic spoon, large long handle, and small plastic tweezers, a piece old Pyrex boiler sight glass (to crush powder like mortar and pestle about 1 inch thick and 2inch wide 8 inches long, stainless steel crusher bar, well most any other thing you can find in the kitchen, or at a second hand store, Pyrex coffee pots, crock pots, blender, coffee mug warmers, wine separator funnels, battery jars, stainless steel pans, pickle jars, canning jars, well I could go on and on.
Another thing to consider my hot plate has a solid cast iron burner with wire heating coil inside, so my dish heats evenly, and holds up well with hot plate on high and propane torch incinerating powders from above.
I would be a little worried about putting the dish directly on the coil type burner like your using, I would probably put a flat steel metal plate between coil and dish. I really do not know if this would give you trouble.
The best way to eliminate nitric from Aqua Regia, is not to add it in excess to begin with using only the exact amount needed to oxidize the gold with no excess.
Evaporation of nitric from Aqua Regia is easy, but it is one process you should also learn when you have to keep an eye on it and when you can relax and let the process work while your not watching it.
Dilute solutions will mostly vapor of water.
Lets look at nitric and water alone for a second, a dilute nitric solution will vapor off mostly water, the nitric acid in solution will concentrate (up to a point) up till its azeotropic point, for nitric acid that is 68% in solution (the highest concentration you could achieve for nitric acid by this method), then the acid will come off as vapors (68% acidic vapor fumes) until the nitric was gone from the vessel.
Ok now lets look at just HCl and water, very similar a very dilute HCl will vapor off mostly water, the acid will concentrate to its azeotropic point, at this point around 20 something percent (bad memory) at this concentration the acid will not get any higher and now the fumes will vapor off 20 sum percent HCl.
Also the boiling points of these acids change with concentration, (similar to how pure water and salt water have very different boiling points)
Now Aqua Regia, evaporating a dilute solution, water would be the first to vapor off (little acid fumes)(and gases created in reaction), then mostly nitric fumes, then HCl fumes,
Now Aqua Regia is a bit more complex than a single acid and water, and there are several chemical reactions going on inside (several gases being formed, we also have metals reacting with these chemicals, so it is more complex than one acid in water).
When we first start evaporating we are concentrating these acids vapors of water and the gases formed escape, but once these acids and metal salts concentrate (the fumes begin to contain more of the acid, (also the boiling points change), and the acid solution may suddenly boil over at a certain point even though you have not raised the temperature, then after this acid has mostly been eliminated the solutions boiling point may change again as mostly just one remaining acid is left with the metals salts dissolved.
What I am trying to say, keep temperature below boiling point, you want it to evaporate not boil (fumes will come off below boil) (think how the sun can evaporate water from a pool), (the sun does not need to boil the water), this slow evaporation will remove fumes as dilute acid mostly water as the solution concentrates the acids azeotrope and then more nitric (NOXX fumes), will be in gases.
Take note here:
When solution gets to a certain concentration you will see tiny bubbles form around edge of pot, is a sign that you may get a boil over, even though you did not change the temperature of the solution evaporating,(quick turn down the heat)( this is where nitric will start boiling off violently seems like it is trying to come out all at once) (boil over and loose your gold), by watching closely after acid concentrates and turning down heat here you will prevent that, after a little bit (gases escape the heat can be turned up again (you can relax you passed what I call the nitric boil over point).
Points to remember slow evaporation do not boil.
Do not breath fumes.
When starts to concentrate watch closely for small bubbles (they are subtle small bubbles), lower heat until reaction stops (reacting),
(A water mist spray bottle is always handy when most any type of solution tries to boil over, the water sprays down bubbles, cools and dilutes so gases dissolve so keep a mist water spray bottle handy).
Concentrate to thick syrup but not to salts (or baking gold salts to vessel (here is where Hoke recommended few drops of sulfuric acid in solution, that would help to prevent salts from forming so easily and also help some to rid nitric),
Add just a little HCl (not too much your just getting the solution diluted some and (keeping wet from forming salts with more heating, and driving off some remaining NOXX gases (nitric fumes), I repeat this three times. the last time I dilute four time volume with water, let sit overnight or longer for silver chloride to precipitate.
Throw that urea in the yard your grass and gold will be better for it.
Ok I am tired and flapped my jaws enough, I have not had much sleep so I do not even know if any of this makes any sense or not. Good night.
