# Urea oh urea



## Metallurgist (Feb 27, 2012)

Hello fellows am from nigeria and am having difficulties with using urea disolved in warm water to eliminate nitric acid, first it wont fizz at all and after several addition it precipitate into white cristals i filter and add SMB but no gold drop in over 30 hrs, am really frustated giving am new to the process, urgent help needed pls on any useful method of adding the urea,


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## 4metals (Feb 27, 2012)

Do not mix it with water as you will not be able to see the reaction and you will add too much. Which is apparently what has happened already. 

Use dry urea, preferably in the form of prills, little balls of chemical about the size of BB's. sprinkle it on top of the acid and you will see a strong reaction which will foam up. Make sure you have enough height in your container to contain the foam. Generally it can expand to double its original volume. 

When the reaction nears completion you will see the small prills of urea floating when you add some more. Continue adding small amounts until you see the prills float and you're done.


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## Metallurgist (Feb 27, 2012)

Hi thank you for the reply but still the problem persist when i add the dry urea( though its in small cristals like table sugar) its just settled at the bottom and dissolved slowly into the solution with no any visible reaction, fizzing,or forming.I bought the urea from a chemistry lab store and am sure its a good grade am really confuse on how to get rid of the nitric acid any method other than the classical method is highly welcome thank u.


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## jimdoc (Feb 27, 2012)

Please just keep one thread going on this subject. 
Thanks.

Jim


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## rusty (Feb 27, 2012)

Metallurgist said:


> Hi thank you for the reply but still the problem persist when i add the dry urea( though its in small cristals like table sugar) its just settled at the bottom and dissolved slowly into the solution with no any visible reaction, fizzing,or forming.I bought the urea from a chemistry lab store and am sure its a good grade am really confuse on how to get rid of the nitric acid any method other than the classical method is highly welcome thank u.



Perhaps your one of the lucky ones who does not use nitric in excess, maybe your nitric is all used up.


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## Metallurgist (Feb 27, 2012)

Bear with me pls, am a nigerian my home town has a good local gold deposite which i extract at my first experiment using sodium cyanide solution to leached the gold out and precipitate it out using zinc powder i then use aqua regia to dissolve the zinc precitate and then use used the classical method to eliminate the nitric acid and then add ferrous sukphate i got a red brown mud as expected but upon repeating the experiment on one kg of the ore but using both dry urea and urea in solution no visible reaction or fizzing and no gold precipitate at filtering and adding ferrous sulphate in both cases, i posted and jim reply that may be i use up all my nitric acid, is there any simple mean to determine when the nitric acid in aqua regia is used up? Thank you!


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## jimdoc (Feb 27, 2012)

Why do you keep starting new posts on the same topic? This makes 3 different threads about the same problem. Just respond to the original post and keep all of the information in one thread, so people understand what you are talking about. And it was Rusty that answered your question, not Jim.

Jim


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## niteliteone (Feb 27, 2012)

What is the temperature of your solution?
The urea does it's job the best when added to a solution that is about 160*F.
On a solution that is cold it will take longer or not work at all.

Tom C.


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## rusty (Feb 27, 2012)

Metallurgist said:


> Bear with me pls, am a nigerian my home town has a good local gold deposite which i extract at my first experiment using sodium cyanide solution to leached the gold out and precipitate it out using zinc powder i then use aqua regia to dissolve the zinc precitate and then use used the classical method to eliminate the nitric acid and then add ferrous sukphate i got a red brown mud as expected but upon repeating the experiment on one kg of the ore but using both dry urea and urea in solution no visible reaction or fizzing and no gold precipitate at filtering and adding ferrous sulphate in both cases, i posted and jim reply that may be i use up all my nitric acid, is there any simple mean to determine when the nitric acid in aqua regia is used up? Thank you!



Add a gold button, when the aqua regia no longer dissolves gold from the button your nitric is all used up.


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## dtectr (Feb 27, 2012)

My friend 
The most "basic" is that described by Hoke in what is essentially the bible for this forum. That is an evaporation (NOT "BOIL") to syrup or honey-like consistency, followed by the addition of hydrochloric acid. If nitric is still present, you will see it dissipate as brown fumes. Repeat for a total of 3 evaporations. 
You may already be past this as stated above. 
My friend, for your safety and that of those you love, please take whatever time is necessary to understand the processes involved for the type of material you are handling. We will help if you are willing to do your part. Good luck!


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## Metallurgist (Feb 28, 2012)

Thank guys i test my urea on a fresh aqua regia and got both the fizzing and foaming so i guest my my pregnant aqua regia has no excess nitric acid. Can i precipitate my gold with all the form and cristals that precipitate or do i have to filter or something thank you very much


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## 4metals (Feb 28, 2012)

Add hot water until you dissolve the crystals and then drop the gold. Add as little extra liquid as possible, often warming the acid alone will dissolve the crystals. 

Do not drop the gold with crystalline urea on the bottom as it will be a mess to clean up the precipitated gold and often the crystals trap solution which cannot react to the precipitant.

If it is a huge amount of crystal, filter it out before dropping but remember there will still be gold bearing solution in the crystallized urea.


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## Metallurgist (Feb 28, 2012)

Thank u 4metal even though the water will be hot is there no hazard in adding water to an acid and not the way around thanks


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## butcher (Feb 28, 2012)

You can add water to aqua regia solution safely.

It will not boil like it would if you tried that with concentrated sulfuric acid.

As you already understand.

Never add water to concentrated sulfuric acid, always add the acid to the water, for safety.

The trick of adding gold to a saturated solution of heated aqua regia is a very valuable method to remove the free nitric acid from solution, it is quick (no need for evaporation), and will not add other chemicals to the solution, which may give troubles, and you get the gold back.


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