Bad Urea

[Ayham Hafez]

I was sure that urea is not the best way to denox nitric, but I used it since sulphamic acid is not available in my country, but recently I had a bad experience with urea،I read that urea reaction with nitric is only generate H2O, but I think its much complicated since in my case it seems to react with other metals in dirty aquaregia solution and stop the work of SMB and ferrous sulfate, my advice for all is STOP USING UREA AT ALL!

 

[Yggdrasil]

I was sure that urea is not the best way to denox nitric, but I used it since sulphamic acid is not available in my country, but recently I had a bad experience with urea،I read that urea reaction with nitric is only generate H2O, but I think its much complicated since in my case it seems to react with other metals in dirty aquaregia solution and stop the work of SMB and ferrous sulfate, my advice for all is STOP USING UREA AT ALL!

If you use too much it will neutralize the solution by pushing the pH too high.
Urea is caustic.
Especially SMB needs the pH to be low, I think this is also true for Ferrous Sulfate.
This is already covered in the forum.

 

[Ayham Hafez]

If you use too much it will neutralize the solution by pushing the pH too high.
Urea is caustic.
Especially SMB needs the pH to be low, I think this is also true for Ferrous Sulfate.
This is already covered in the forum.

In my case I didn't add too much urea, I just start with spoon with 20 liters aquaregia then I noticed that the reaction is not normal so I stopped adding, I think issue is urea reaction with other metals, PH is still 1 but gold not dropped at all so I cemented it.

 

[Southfork]

Just visiting is exhaust fluid urea and mineral water the same chemical?

 

[orvi]

Just visiting is exhaust fluid urea and mineral water the same chemical?

If you mean AdBlue (named like this in EU) - additive to the next-gen diesel combustion engines, then yes, it is practically very concentrated urea solution in water. But it can contain some other additives.

 

[eaglekeeper]

Just visiting is exhaust fluid urea and mineral water the same chemical?

Most people get urea in it's dry form, DEF is pretty much the same... 32-35% urea and water. We service our buses with DEF every day...I hate getting that crap on my hands.

I was sure that urea is not the best way to denox nitric, but I used it since sulphamic acid is not available in my country, but recently I had a bad experience with urea،I read that urea reaction with nitric is only generate H2O, but I think its much complicated since in my case it seems to react with other metals in dirty aquaregia solution and stop the work of SMB and ferrous sulfate, my advice for all is STOP USING UREA AT ALL!

You may be able to find Sulfamic acid locally as a tile and grout cleaner. Read the label to make sure it's just Sulfamic acid.

 

[Yggdrasil]

If you mean AdBlue (named like this in EU) - additive to the next-gen diesel combustion engines, then yes, it is practically very concentrated urea solution in water. But it can contain some other additives.

Usually Formic Acid in some concentration.

 

[Yggdrasil]

In my case I didn't add too much urea, I just start with spoon with 20 liters aquaregia then I noticed that the reaction is not normal so I stopped adding, I think issue is urea reaction with other metals, PH is still 1 but gold not dropped at all so I cemented it.

If you made AR the conventional way you would have liters of excess Nitric.
Cementing works though.

 

[Martijn]

In my case I didn't add too much urea, I just start with spoon with 20 liters aquaregia then I noticed that the reaction is not normal so I stopped adding, I think issue is urea reaction with other metals, PH is still 1 but gold not dropped at all so I cemented it.

20 liters! What were you processing?

 

[Shark]

If you add too much copper into AR, it is possible for nitric to cause issues. Think in terms of boards and some pins or CPU’s. It can be next to impossible at times to neutralize the excess, in that it may re-generate some nitric or NOx. I do not claim to understand how it works, but have read about it and seen it happen when running some CPU’s in AR. Even sulfamic struggles to eliminate the excess. Heat as well won’t keep it out and may even aid the nitric in reforming.
Urea does not stop nitric but kills the NOx. If the filtration is done quickly you can drop the gold but it must be done and the gold removed before the nitric starts to re create AR and the gold starts going back into solution. Things like this is just a few of the reasons many experienced refiners keep saying “this isn’t as easy as it looks” especially where YouTube is concerned.

Like I said, I can’t scientifically explain this but have read briefly about it as well as seen it happen several times.

 

[FrugalRefiner]

Copper is one of those metals that is content to exist in multiple oxidation states. We use it in the CuCl₂ leach (AP) as the copper goes back and forth between CuCl₂ (where the copper is Cu²⁺) and CuCl (where the copper is Cu⁺). It can do the same thing in AR, and as it's oxidation state lowers it gives off NO₃.

Dave

 

[Shark]

Copper is one of those metals that is content to exist in multiple oxidation states. We use it in the CuCl₂ leach (AP) as the copper goes back and forth between CuCl₂ (where the copper is Cu²⁺) and CuCl (where the copper is Cu⁺). It can do the same thing in AR, and as it's oxidation state lowers it gives off NO₃.

Dave

Probably the best explanation I have heard for this. There could be good uses for this if one could learn to control it I would think. But it is beyond my know how.

Ha… by quoting Dave’s post I see how they add that little number to the formulas… now if I can remember it …

 

[FrugalRefiner]

Ha… by quoting Dave’s post I see how they add that little number to the formulas… now if I can remember it …

There's a button for it. At top of the edit box there is a row of buttons/controls for Bold, Italic, Type size, text color, etc. Click on the first button with 3 vertical dots. Another row of buttons will drop down. You should see a superscript, subscript, font family, strikethrough, etc.

So just type out your text. Then select the text you want to modify, and click the button. Easy.

Dave

 

[Shark]

There's a button for it. At top of the edit box there is a row of buttons/controls for Bold, Italic, Type size, text color, etc. Click on the first button with 3 vertical dots. Another row of buttons will drop down. You should see a superscript, subscript, font family, strikethrough, etc.

So just type out your text. Then select the text you want to modify, and click the button. Easy.

Dave

That easy…..

Now to learn when to sub and when to sup. Never ending quest to refining and chemistry.

 

[FrugalRefiner]

Probably the best explanation I have heard for this. There could be good uses for this if one could learn to control it I would think. But it is beyond my know how.

Hoke uses it in the classic separation of platinum and palladium. She uses ammonium chloride to precipitate platinum, then adds sodium chlorate to precipitate the palladium. She doesn't cover the chemistry.

Palladium(II) chloride (PdCl₂) will remain in solution until it is oxidized to palladium(IV) with sodium chlorate, whereupon it will precipitate as a hexachloropalladate (PdCl₆^2-). But if the palladium (or some of it) is already oxidized to +4, some will precipitate along with the platinum, which makes complete separation difficult.

Dave

 

[Shark]

Hoke uses it in the classic separation of platinum and palladium. She uses ammonium chloride to precipitate platinum, then adds sodium chlorate to precipitate the palladium. She doesn't cover the chemistry.

Palladium(II) chloride (PdCl₂) will remain in solution until it is oxidized to palladium(IV) with sodium chlorate, whereupon it will precipitate as a hexachloropalladate (PdCl₆^2-). But if the palladium (or some of it) is already oxidized to +4, some will precipitate along with the platinum, which makes complete separation difficult.

Dave

Just another good reason to read Hoke’s book. We learn some chemistry without even realizing it. And if we can’t learn chemistry we can still learn to refine the gold (and other metals) we already may have.

 

[Ayham Hafez]

20 liters! What were you processing?

Some low grade pins with their plastic

 

[Martijn]

how do you deal with waste?

 

[orvi]

Probably the best explanation I have heard for this. There could be good uses for this if one could learn to control it I would think. But it is beyond my know how.

Ha… by quoting Dave’s post I see how they add that little number to the formulas… now if I can remember it …

Understanding complicated AR chemistry is a good skill that you can benefit later. It is very interesting how addition of one extra acid could complicate so many things.
CuCl2 vs CuCl in AR solutions is real thing, and CuCl has some appreciable solubility in it, before it starts to precipitate. It is of no major use tho - aside from visual control of redox potential - which is very good thing to know. Eventually, CuCl can keep copper dissolved in solution (some fraction of copper) with just one electron oxidation and one chloride anion. So in theory, you can benefit from this fact and add some more copper material into it and dissolve some extra material without additional acid.

CuCl2 in solution is very deep green, but visually green colour. CuCl is colourless. But if there is solution of mixed CuCl2 and CuCl, it change colour to deep brown. If you see this, you know you have mutual presence of Cu(I) and Cu(II) in solution, and this solution isn´t capable of redissolving gold in usual scenario. This is also a good thing to notice when you drop gold from saturated base metals AR solutions - if the liquid is brown, you probably added enough SMB "one spoon ago"