Urea observations.

[limestonecowboy]

I have been processing mostly karat gold in proper AR -(3/1 HCL/NHO3)for several months and made an interesting observation.

I accidently dropped a few beads of urea into a 'not quite finished' batch of watch cases. A minute or two later, after the instant fizzing of the urea beads had died down I noticed a distinct acceleration of the speed at which the remaining metal was bubbling.

I presumed that maybe I had too much nitric in the mix and the urea had created a better balanced mixture.

I was curious.

So I made up several different blends of AR, each having equal temp and volume, but with varying proportions of HCL/NH03.

I proceeded to dissolve an equal ammount of 9ct gold in each.

Each mixture was observed to disolve the metal at a slighly different rate, as was expected.

After 1 hour, a tiny ammount of urea was added.

In all but one (very low NHo3) there was a marked rejuvenation in the gasses given up from the remaining metals.

What I want to know is...

Is the observed increase in gassing caused by the increase in which the solution is attacking the metal, or is there some other process that is causing this ?


Forgive me if the topic has been covered elsewhere,


and yes I have hoke.

Cheers

Richard

 

[Platdigger]

In your mixture with the least amount of nitric.....
what was the ratio of nitric to hcl?
Randy

 

[butcher]

Urea (NH2)2CO increased gas maybe carbon monoxide (CO), and CO2,
if heated can also evolve ammonia(NH3),
this would bust up some of your NOCl so nitric action may also decrease the aqua regia's abillity to dissolve gold,or even keep NO2 in solution :
urea also can change NOx gas if water in solution back into HNO3, the brown gas mixing with water, if you have increase in action on gold this is may explain why, your nitric is not gassing out as NO2, but mixing with water reforming back into nitric acid picking up hydrogen and oxygen from water. urea in very small quantity's can keep NOx gases in nitric if some water present, hydrogen peroxide can also do this, and this can be why dilute nitric can attack base metals better than concentrated acid can, keeping NOx (NO2 brown gas)in solution,

 

[limestonecowboy]

In your mixture with the least amount of nitric.....
what was the ratio of nitric to hcl?
Randy

Platdigger, the weakest mixture was just 10% Nitric.