Urea - wont denoxx in volume.

I have been working on an experiment with ceramic processors. It involved an excess of A/R.
In trying to denoxx I always add a few prills of urea to see the reaction and it helps me judge how much urea is needed to denoxx a batch.

With this solution I added a few prills and got no reaction. they just floated on top. Unusual as I knew there was an excess of nitric. Added a few more and stirred well. No typical reaction. They did dissolve with lots of stirring. NO fizz, no foam, nothing.

Added a 1/4 teaspoon smb-- Lots of fizz, foam, strong reaction..no drop.

Pulled a 20 ml dip sample, added a prill or 2, no reaction.... added a tiny amount of smb, lots of fizz, nice powder drop instantly.

pulled a 200 ml dip sample no reaction to urea...lots of fizz nice gold drop with smb.

Back to the main batch.. No reaction to urea, violent reaction to smb. No drop. Tried urea and smb additions several times.

I am at a loss as to why there is no reaction to the urea, the smb goes crazy in the main batch but there is no drop.

Is my solution not dilute enough? Do I need heat or cold? What am I missing? Any help appreciated. Mike

Skip the urea. With dry SMB additions you may notice a red-brown fume above the solution indicating excess nitric acid. With this condition you are likely redissolving the gold as it precipitates forming the foaming you mentioned.

Keep adding SMB (most likely more than normal) to burn off the excess nitric (red-brown fumes). Add some, stir, let the red-brown fumes and foam clear, then add more as needed until your solution goes dark and calms down with new SMB additions. When you smell SO2 you are likely near the end point of the SMB additions. A little water may also help if the solution is very concentrated.

Heating may cause the gold to re-dissolve if there is still excess nitric in the solution. If so simply add more SMB and water if necessary. If you are seeing solid SMB in the bottom of the container you need more water.

When you get it right the color of the foam should go from a yellow color to crisp white. Just before it goes white you'll see a deep brown/ purple color to the foam as the SMB levels reach the proper amount. I add a little more at this point to make sure the foam is white and the nitric is destroyed.

Remember you need lots of stirring to expose the SMB to the moisture in the solution.

Test all solutions before properly disposing of them.

Steve

Thanks Steve. I do get that nice red floating on the foam with every addition and watch for the foam to change to white but no luck yet. I will continue with smb, but darn it I am running out. If I don't have enough I will resort to copper cementation.
Any idea why the urea won't work? Its good to know I am on the right track, just the wrong train :lol:

Glondor, is your solution hot or cold?

I ask because when I ran the left over ceramics, I also added a bit extra nitric, (its harder for me to calculate how much nitric when doing ceramics than jewelry), so when I added the SMB to the cold solution, & no reaction, I then added the urea & also no reaction; but when I heated the solution a reaction took place & the gold dropped.
On the following batch I added the urea while the solution was hot & there was a reaction. Then I let the solution cool, added the SMB & the gold dropped.

I don't really know... maybe it was just one of those times... :roll:

Phil

Glondor,

Have you tried using sulfamic acid instead of urea? It has it's own little quirks, but I still like it 100 times more than urea. It's very predictable. In 50# bags, I paid $0.58/# within the last year..

To all:

The best way, of course, is to not use an excess of nitric to start with. That way, you can drop the gold without any need to fiddle with the solution. I would guess that, in at least 90% of the cases, one can avoid using an excess, mainly by following the incremental addition procedures that I first introduced to the forum. In rare cases, one is forced to use an excess. I recently was working with a high HNO3/low Cl- solution to dissolve gold in a weird application. I ended up using sulfamic acid to kill that huge amount of nitric, with great success.

Depending on the volume of the solution you could dissolve your urea in hot water before adding to see if Phil's idea will work. I don't use urea so I'm not going to be much help when it comes to the best way of using it.

Steve

goldsilverpro said:

Glondor,

Have you tried using sulfamic acid instead of urea? It has it's own little quirks, but I still like it 100 times more the urea.

Click to expand...

Now I do use sulfamic, but only on high nitric solutions that I intentionally used a lot of nitric in (eg: reverse AR), never for normal AR reactions.

Sulfamic works in my applications either wet or dry, but best when hot.

Problems I've noticed with sulfamic acid are it's poor solubility and lots of foaming which is expected when producing insoluble gases in any liquid. All in all it's one of those things I only use when necessary and then only in minimal amounts as required. If using sulfamic wet (dissolved in hot water) you can expect your solution volume to increase by at least 1.5 times it's original volume when the reaciton ceases and possibly as much as three times it's original volume during the foaming process. There are also the effects of the nitrous (N2O) off gassing that you need to be aware of.

Steve

Thanks guys. I am at the lab now. Was hoping for some reaction over night but no joy. Just prills of urea floating on top. I will add smb until I am almost out. Tried some heat already but no change. ( I am evaporating 1/2 of the solution for denoxx with hcl). I will save a bit of smb for that. I do have a pound of oxalic acid I can fall back on as a last resort.

glondor


Dissolve your SMB fisrt in hot water, about 50mL for every teaspoon.
I find it useful in such cases.

Thanks all for your help. 3 spoonfulls of smb did the trick. Thanks for all the ideas of methods as well. I will do the remaining half bt the evaporation HCL method and see how that goes as I have never tried it before. If all goes well I will post results from the material and identify what the gold came from.

They that want their concentrated gold chloride solutions to be cool when adding SMB neglect to heat the solution to 72C (160F)
prior to adding urea. Urea doesn't work well in at cool temperatures. If you must use it, then use it hot. You can wait a little for the solution to cool to add your sodium meta-bisulfite. Also I've notice that very few here on the forum raise their solution's pH to the normal pH-1.5 before trying to precipitate (working scrap gold). pH-0 is a hundred and fifty times more acidic than pH-1.5. The numbers on the pH scale are logarithms of ten for proton hydrogen available. The higher the pH, the more alkaline or less acidic is the solution. I suppose that since the SMB has sodium hydroxide in it's formulation, that they are relying on that to raise the pH. Dr. Poe :roll:

Thanks a bunch everyone. All dropped and melted. For what I believed the material to be the results are not believable. I will do some investigation. This stuff looked like crushed ceramic processors. Maybe Pentiums or something similar. Same colour, same pins. Client from out east sent them as just ceramic processors. It is late i will post more tomorrow.

So you got more than expected, or less than expected?

lazersteve said:

Depending on the volume of the solution you could dissolve your urea in hot water before adding to see if Phil's idea will work. I don't use urea so I'm not going to be much help when it comes to the best way of using it.

Steve

Click to expand...

To Steve's point, when I have to burn off excess Nitric, I do it when the AR solution is at room temp, but I melt the Urea in a small beaker of DI water before. I put it on the heat pad and let it warm up and throw in a stir bar and stir until it's all melted. Then I add small amounts until I have no more reaction. This may all be in my head, but for whatever reason it seems that Urea works better when the solution of Urea you are pouring into your AR solution is warmer than the AR.

I am using poor man's AR as much as possible, I realized that it's more difficult to observe when you should stop adding sodium nitrate. It is much easier if you dissolve the sodium nitrate in DI water first. Then add like nitric until you see your stopping point. I rarely need to burn off excess nitric now days, since I started doing my poor man's AR this way.

So far as Urea not driving off the excess nitric acid, you may not have a dilute enough solution. Heating and adding water usually works. If you are using a low grade Urea you may have other issues. Look at your prilled Urea under a loop. If it has a shiny surface then it was probably exposed to humidity or the weather.

In the Ukraine, where most Urea comes from, they set the Urea out in the open, in huge piles. Even bagged it sits outside. I used to broker deals on Urea used to fertilize, the quality of the Urea was always in question. I always had to have it inspected by a third party for quality before the bank would release the letter of credit. Unfortunately, the quality was often not up to par.

@Sbrown,
By melted, I presume you mean, dissolved?

Well. I did post the result of this before but took it down as it is just not to be believed. 3 pounds ceramic processors, crushed to 1/4 minus, magnetically separated, no barren ceramics no lids, no center chip section. (which means no bonding wires) just the pins in ceramics. 25g au true. Needless to say the customer was thrilled, I was baffled and all was good. 8+ g per pound. Never figured out why and have not seen the material again.

Lou said:

@Sbrown,
By melted, I presume you mean, dissolved?

Click to expand...

Melts and dissolves into water. At 134°C (273°F) Urea starts to melt, to make sure I fully dissolve Urea into water, I take the water all the way up to 135°C, so I assume, and I hope rightfully so, that I am not only dissolving, but melting so that it dissolves better, into water.

Please correct me if I am wrong. To make it clear, yes I mean dissolving and you were right to point that out, but I did mean melting as well.

SBrown said:

Lou said:

@Sbrown,
By melted, I presume you mean, dissolved?

Click to expand...

Melts and dissolves into water. At 134°C (273°F) Urea starts to melt, to make sure I fully dissolve Urea into water, I take the water all the way up to 135°C, so I assume, and I hope rightfully so, that I am not only dissolving, but melting so that it dissolves better, into water.

Click to expand...

Unless you have water under pressure, it can't be heated beyond 100°C. Impossible, as it no longer is water, but steam.

You are not melting. You are dissolving. They are not one and the same. It is important that you understand the difference, and that you use proper terminology. Others with less knowledge are trying to learn.

Harold

:mrgreen:

Harold_V said:

SBrown said:

Lou said:

@Sbrown,
By melted, I presume you mean, dissolved?

Click to expand...

Melts and dissolves into water. At 134°C (273°F) Urea starts to melt, to make sure I fully dissolve Urea into water, I take the water all the way up to 135°C, so I assume, and I hope rightfully so, that I am not only dissolving, but melting so that it dissolves better, into water.

Click to expand...

Unless you have water under pressure, it can't be heated beyond 100°C. Impossible, as it no longer is water, but steam.

You are not melting. You are dissolving. They are not one and the same. It is important that you understand the difference, and that you use proper terminology. Others with less knowledge are trying to learn.

Harold

Click to expand...

Thank you for the correction Harold. I'll make sure I use dissolved, I didn't even think about the temp of the water itself.