# Urea to eliminate excess Nitric Acid



## Wilo (Aug 13, 2017)

Hai I am new to this forum and currently I am doing some refining gold from electronic scrap mostly are PCBs from mobile phones. This forum is very helpful for me as when something goes wrong I will look for the solution here.

So I managed to get the gold dust which I am not sure if it is the right dust as the color are brownish after I put the SMB into Aqua Regia solution. However there are things that I am not sure if I am doing it right and confused with the usage of Urea to eliminate the excess nitrate. Some people say in this forum to use Urea but some are not as Urea is very dangerous when mixing with Nitric Acid. I got scared and find another way to get rid of this nitrate such as evaporation and addition of water. But it does not work as when I put a lot of SMB into the solution the brownish fume came out and it does not precipitate the gold. So I tried to put Urea and SMB again and it worked. yes it did precipitate the gold.

So my question is if the using Urea is correct way? is it safe? since some says it could be explosive

Appreciate if some can answer my question.

Thanks


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## jason_recliner (Aug 13, 2017)

Firstly, welcome to the forum. If I understand correctly what you've explained:


> I got scared and find another way to get rid of this nitrate such as evaporation and addition of water


In the nitric evaporation process, you do not add water, but add HCl. Some free acid is required for the SMB to do its work.



> solution the brownish fume came out and it does not precipitate the gold


That brown cloud IS precipitation. It's only that excess nitric may then cause it to re-dissolve.

If you add your nitric patiently, in small increments, you will not have this problem.
Keep the urea for growing plants.


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## nickvc (Aug 13, 2017)

Welcome to the forum.
We advise using sulphamic to rid nitric if an excess has been used but the best advice is to cover your material with plenty of Hcl and slowly add small amounts of nitric until you get no reaction, this should eliminate the need to neutralise the nitric.


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## jimdoc (Aug 13, 2017)

Wilo said:


> This forum is very helpful for me as when something goes wrong I will look for the solution here.



You are supposed to study this forum, to know what you are doing before "something goes wrong". 

Things go better when something doesn't go wrong. It is always better to learn from others mistakes. Doing your homework helps to prevent hazardous or costly mistakes.

Jim


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## g_axelsson (Aug 13, 2017)

Wilo said:


> I got scared and find another way to get rid of this nitrate such as evaporation and addition of water. But it does not work as when I put a lot of SMB into the solution the brownish fume came out and it does not precipitate the gold. So I tried to put Urea and SMB again and it worked. yes it did precipitate the gold.


Hi and welcome to the forum.

Urea is used by some people but the consensus on the forum is that it isn't needed if you manage your nitric uses or add a gold button to use up extra nitric at the end. Urea doesn't guarantee to remove all the nitrates and in some cases could form explosive compounds. It can also complicate things if you have PGM:s in solution. For some other discussions, check the links on this page.
http://goldrefiningwiki.com/mediawiki/index.php/Urea

I have never used urea.

When using evaporation you should add HCl and not water. This will remove even nitrates. If you got a brown gas cloud when adding SMB then you still had some nitric acid left with your gold chloride. Properly denoxed solutions doesn't produce any red or brown fumes.
http://goldrefiningwiki.com/mediawiki/index.php/Denoxing

Göran


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## butcher (Aug 14, 2017)

Göran, 
The GoldRefiningWiki ( http://goldrefiningwiki.com/mediawiki/index.php/Main_Page ) has really come a long way, looks like you have put an awful lot of work into it Very Nice.


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## g_axelsson (Aug 14, 2017)

butcher said:


> Göran,
> The GoldRefiningWiki ( http://goldrefiningwiki.com/mediawiki/index.php/Main_Page ) has really come a long way, looks like you have put an awful lot of work into it Very Nice.


Thanks, I add to it now and then when I have time.

 

This is how I envisioned the wiki from the start. A better place to collect references and in dept information, easy to find information and expand when new discussions on GRF appear. With links to good threads on the forum as references.
There is a lot more to do though, the wiki is merely started in my mind.

Göran


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## Wilo (Aug 15, 2017)

> You are supposed to study this forum, to know what you are doing before "something goes wrong"



Yes I did study this forum before I put to work but sometimes there are so many versions of it that I did not know who to follow



> That brown cloud IS precipitation. It's only that excess nitric may then cause it to re-dissolve.
> 
> If you add your nitric patiently, in small increments, you will not have this problem.
> Keep the urea for growing plants.



What do you mean by add nitric? 



> When using evaporation you should add HCl and not water. This will remove even nitrates. If you got a brown gas cloud when adding SMB then you still had some nitric acid left with your gold chloride. Properly denoxed solutions doesn't produce any red or brown fumes.
> http://goldrefiningwiki.com/mediawiki/i ... p/Denoxing



I tried to add HCL also but there was no brown cloud coming out from the solution. it did not have any reaction just like adding water.


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## Wilo (Aug 15, 2017)

So I have managed to get the dust but now I am not sure whether it is the right dust since when I melted everything there was no gold found. I put the images below 







The last image is after I melted it

Can anyone help to explain? 

Thanks a lot


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## jason_recliner (Aug 15, 2017)

> What do you mean by add nitric?


This is what others are also trying to tell you. Instead of mixing up a 3:1 (or whatever) ratio of HCl and HNO3 and calling it Aqua Regia, which will have far too much nitric in it, add your nitric in small, incremental quantities.



> I tried to add HCL also but there was no brown cloud coming out from the solution. it did not have any reaction just like adding water


Most likely you did not evaporate far enough. It doesn't work unless you get down to a reasonably thick syrup. Check out Hoke's guide to evaporation, it's all you need.



> Yes I did study this forum before I put to work but sometimes there are so many versions of it that I did not know who to follow


Then stop. You really should not proceed until you understand what you are doing, why you are doing it, and the result you expect to achieve. You can't just play with this, you could get hurt.


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## jason_recliner (Aug 15, 2017)

Wilo said:


> The last image is after I melted it
> Can anyone help to explain?


I don't mean this disrespectfully on a personal level, but perhaps being a little blunt is warranted.
Clean, light tan coloured, well refined gold powder IN = shiny gold OUT.
Dark mix of all sorts of random crap IN = ???

The good news is that if there's gold in there, it'll still be there when you've learned to refine clean powder. This site is full of example images of clean powder. When you can make that, you're ready to start melting it.

Walk before you run.


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## g_axelsson (Aug 15, 2017)

That does not look like gold, more like brown rust. I wonder if SMB + tin in solution would give a brown precipitate? SO2 left after precipitating gold could give a brown false positive when testing with stannous so it seems logical to assume that a lot of tin chloride in solution would drop as a brown sludge of tin sulfide if mixed with SMB in acidic conditions.

This also means that if there is tin in solution there shouldn't be any gold chloride left. Maybe it exists as a colloid at this stage, maybe it's still with the solids filtered off.
- Did you save the solids when filtering the gold chloride?
- Did you save the "barren" solution after filtering off the "gold"?
- Was there a lot of gray sludge that was slow to filter?
- What exactly did you do before precipitating "gold"?
- How much scrap did you start with and how much gold did you expect?
In bullet form, please.

Before precipitating the "gold", did you test the solution with stannous?

Göran


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## Topher_osAUrus (Aug 15, 2017)

g_axelsson said:


> That does not look like gold, more like brown rust. I wonder if SMB + tin in solution would give a brown precipitate? SO2 left after precipitating gold could give a brown false positive when testing with stannous so it seems logical to assume that a lot of tin chloride in solution would drop as a brown sludge of tin sulfide if mixed with SMB in acidic conditions.
> Göran



That is a really clever answer Göran, and I would bet money on you being correct.

The more I read about smb/->SO2 precipitation, the more I come to understand there are several instances where it is not truly selective.
Mainly that "non selective" nature comes from its converting chloride species to sulfur compounds. Silver, lead, palladium, (and now) tin...and I'm sure there is probably more.


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## Palladium (Aug 15, 2017)

Topher_osAUrus said:


> g_axelsson said:
> 
> 
> > That does not look like gold, more like brown rust. I wonder if SMB + tin in solution would give a brown precipitate? SO2 left after precipitating gold could give a brown false positive when testing with stannous so it seems logical to assume that a lot of tin chloride in solution would drop as a brown sludge of tin sulfide if mixed with SMB in acidic conditions.
> ...



Yep! Kinda my observation and theory. Don't know the science behind it, but over gassing by adding to much smb will drop more than just gold.


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## anachronism (Aug 15, 2017)

Palladium said:


> Yep! Kinda my observation and theory. Don't know the science behind it, but over gassing by adding to much smb will drop more than just gold.



Yes and no. It really doesn't bring much extra down at all. You can literally shovel the stuff in (a metaphor if I may) and still end up with gold that will clean up beautifully with a proper wash procedure. The information that too much SMB creates low purity gold with a huge amount of base metals is a myth that has been propagated for too long. It doesn't.

Edit: the pictures show the results of a process carried out in a manner that needs improvement, not the results of too much precipitant.


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## Topher_osAUrus (Aug 15, 2017)

anachronism said:


> SMB creates low purity gold with a huge amount of base metals is a myth that has been propagated for too long. It doesn't.
> .



I would say it depends on what base metals are in the mix with the gold, and how much.
Well, not so much "I would say", as numerous published authors "say".
And, I would bet that TK Rose, F.E.Beamish, R Loewen, and H.F Collins didn't just go out on a limb guessing, but did actual true-to-science (and scientific approach) testing.

I agree though, that repeated wash and rinse cycles after precipitation can, and does clean up the precipitated gold greatly.

I have to take my son to preschool stuff here in a minute, but I will get you cited quotes shortly.


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## Palladium (Aug 15, 2017)

I understand his statement. But it's all in procedure and process. For the sake of the uneducated mind we teach to the method of the science. While your statement is somewhat acceptable to the more advanced refiner the newbies are taught to relate to the art of achieving perfection. Causing a problem that doesn't need to be and then justifying it with it will clean up while it may be true is not art or science. It's just getting it done.


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## anachronism (Aug 15, 2017)

The figures constantly quoted for the precipitation of gold using SMB are only applicable in a laboratory setting, or for precipitating from a pure solution of Gold Chloride. As soon as you add "reality" to the situation i.e. Base metals, residual excess nitric, and the resulting differing base metal ionic states among others, then those figures simply go out of the window. 

You'd be hard pushed to precipitate 10g of gold from a dirty AR solution containing 10g of gold using 10g of SMB. It simply doesn't happen.

For example in many cases your base metals are actually effectively redissolving your gold by reacting with the chloride ions. That flies in the face of "accepted lore" however if you read Hoke's page on the stock pot she actually alludes to this. Like so much of what Hoke wrote it was interpreted in an over simplified way because it was presented in such a simplified language. The science itself was masked, and missed. 

As such "getting it done" relies upon all these things and that should be what is taught rather than over simplified stoichiometry. Learning to refine is about learning about the real world and the interactions between everything that lead to the end result. Pretty shiny pure gold. 8)

Being an excellent chemist doesn't make for someone automatically being a good refiner.


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## Wilo (Aug 15, 2017)

> Most likely you did not evaporate far enough. It doesn't work unless you get down to a reasonably thick syrup. Check out Hoke's guide to evaporation, it's all you need.


I read Hoke's book yeah maybe I did not evaporate enough since I thought it will not turn into thick syrup



> Then stop. You really should not proceed until you understand what you are doing, why you are doing it, and the result you expect to achieve. You can't just play with this, you could get hurt.



I don't play with it. I read Hoke's book, I watch video, I read this forum, comments etc. knowing the theory won't get me the gold. I have to give it a try to get the experience and to perfect it. therefore I need your guide to make it perfect 



> - Did you save the solids when filtering the gold chloride?
> - Did you save the "barren" solution after filtering off the "gold"?
> - Was there a lot of gray sludge that was slow to filter?
> - What exactly did you do before precipitating "gold"?
> ...



- yes I still keep the solution
- yes exactly there a lot of gray sludge when first filtering 
- before precipitating, I put Urea into Aqua Regia that has gold flake dissolved in the solution. then I put SMB afterwards
- around 2kg of scrap PCB from smartphone. Before I poured into nitric acid I did some cleaning the PCB to make it clean from any IC

Unfortunately I did not test the solution with stannous as I do not have one. I will buy at this point since it is very important


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## anachronism (Aug 15, 2017)

Hi Wilo

If you started with 2Kg of scrap PCB from smart phones then you will struggle to see the gold precipitated from this. If it I had been old Nokia stuff from the 90s then the yields were quite good but the new stuff is not "good stuff."


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## Palladium (Aug 15, 2017)

Refining is more art that science, but hey! What do I know!


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## butcher (Aug 15, 2017)

Wilo, and all new members thinking they are ready to make the trip to (get) the gold.

The brown powder in the top photo looks like rust (iron powders) there could be several metals in there with iron.
You may or may not have had gold in them.

When many metals get dissolved together into acid, the metal becomes ions of those metals, these metal ions can come back out of solution when they come into contact with a metal that is not dissolved.

Say we have strong acids on a big mix of metals, many metals can dissolve to become salts of those metals in liquid (metal ions called cations). The acid also becomes a salt of the acid called anions.
When metal cations comes into contact with a metal (not dissolved) the metal can trade places with the cations. The cation becomes metal powder coming out of solution, and the metal that was not dissolved, will itself become a cation in solution (trading places, called displacement reactions).

Metals like to trade places in certain ways. The more reactive metals (the undissolved metal in thoughts above) will replace less reactive metal dissolved (cation).
Copper metal replaces gold cations from solution.
Iron metal replaces copper and gold cations from solution.
Zinc metal will replace copper iron and gold cations...
This reaction, we call the reactivity series of metals and displacement reactions).
https://en.wikipedia.org/wiki/Reactivity_series

You may or may not of had gold in those powders.
The gold may just have been replaced by any undissolved metals (left in the trash you were trying to dissolve, or it could be in both places at once (testing is important) our eyes to see the gold when we cannot...
Study how to make your test solution (stannous chloride), which could be made from the electronic solder you have or better with a more pure tin solder you can get very cheap new...

What you need first, is to understand how to process, or prepare your scrap-- before you use any acids.
preparing the trash (or scrap) before is actually more important than using acids to dissolve, or using chemicals to get the metal back.

When we dissolve gold, we do not want to dissolve any other metal if we can help it. We will eliminate all other metals and organic crap first. So we must prepare by getting rid of the other metals first. Sorting the trash from the good, we do this with mechanical processes first. Which is extremely important.
Failure here will be failure with any process.

We may need to also do a pre-dissolve of metals with acid to further separate the unwanted metals (like using only HCl with no oxidizer (or very weak oxidizer, like 3% H2O2 and water), basically we want to get trash out first .
If you put trash in, with your gold, you get trash out, and maybe no gold.

My suggestion (after this is done), is to forget cell phones and PCB mother boards, or any other electronic scrap for now. They are too hard to learn in the beginning, with (too many metals, and some like tin {solder}) that will make a big mess or nightmares.

You need to work with more simple materials and processes, first, to see how it works, and to see how to get gold, and then to get gold pure. This will give you some experience, to put to, all of that study, that you have been doing.

I know you have been reading Hokes Book, it is really basically what you need to understand, but when we read it there are too many new things we are learning new to us, we focus on words that tell us how, but in between these words, we do not see some of the simple messages between her words, like the important steps of preparing the scrap or metals before they ever see acid. Keep reading Hokes as you gain experience, you will then understand the simple but very important messages she teaches.

Collect memory fingers study about them, study copper II chloride leach (called incorrectly, Acid peroxide method, too late to correct that name now.), these you will only deal with mostly copper, some gold, and very little nickle (we remove all solder {lead and tin} in mechanical process), the process is more simple, to recover the gold, dissolving copper and nickle away from it into cations, which can be reused to do more dissolving (saves you big on chemicals and acids). we do not use strong oxidizing acids like nitric that can be much more dangerous,or hard to deal with.
Note: That same process will work much better on the scrap you are trying to work with now...
The way you tried to get gold from your cell phones this time was completely wrong, for that type of materials, to many things to list now.

First learn to get the gold. Collecting scrap, and recovery of the gold, from that scrap, and then we can learn to dissolve it and get it back in a refining process, such as using HCl and bleach (sodium hypochlorite {used to wash white cloths}, where the process is much more simple than using Aqua regia (HCl and HNO3 nitric acid).

Save what you have from this process (mess). Save everything, liquids, powders, melting dish, any parts that you tried to get the gold from, every thing (you have a good chance to get the gold after you gain some experience).

Continue to study the safety section. 
Make a special study of dealing with waste, not only for your safety and others around you. But also much of the principles you will learn there are actually extremely helpful in almost all recovery and refining, a good understanding of the dealing with waste is really very key in understanding many if not most of the principles of recovery and refining, once you understand them well...

It is hard for many people to help you at once, ( it could also confuse you more), there are to many different ways to go, and when you come here asking a question about a problem (like here using a bad method to begin with, aqua regia on electronic scrap, you may get answers of how to get back your gold or what went wrong, but you will not learn much about how to get it right). The raven say's go this way the crow says go to go that way, all of the animals may take a different path to get to the water.

So clean up and pack up this mess, save it for later. 
Collect memory fingers and study, study, study, ask questions about what you do not understand in that study.
Forget about using any chemicals for now, collect scrap, and study (the gold will be there when you are ready).

Study is the and understanding is your treasure map, learn to read the map as you collect more scrap, get the memory fingers while you learn the processes, much later when your ready to start, begin with small experiments, to gain experience with what you have learned, discuss with the forum your plans and procedures, what can go right what can go wrong, what it should look like ... start out simple (not fast), start out slow (Slow and easy wins the race in this game).

This is a very long journey, which is very hard in the beginning, you could be a long time before you really need any acids, (Months or even years, depending on how much you learn first), it takes years and years of study, and we all will study the rest of our lives (as we improve and refine our knowledge and understanding of these sciences and arts, and never learn it all in our life time.

So spending a little time studying before you even open a bottle of deadly and dangerous acids and pour them on metals, which makes deadly fumes or even explosive mixtures, and leaves us with deadly and toxic wastes waters to deal with, that time spent in study and preparing our selves for a life long journey into the field of gold recovery and refining is no big deal for anyone serious about, or willing to learn this profession.

The rabbit, and the turtle had a race, the rabbit knew he was fast, and he thought he was smart, the slow old turtle he did not concentrate on gold, he spent his time studying and asking questions to learn before he took off on his long and slow journey, The turtle spent his time and learned where to go, and how to get there, and the best trails. The Fast young rabbit took off, in a hurry, running fast for the gold. The slow old turtle stopped to study safety. As the rabbit ran up and down the mountains, up and down up and down...

When the turtle was ready he started his long, and slow journey, he stayed on the trail( even though it seemed to be taking him the long way around the big mountains.
The fast ole young rabbit, well he got lost in his hurry to find the gold, lost in the mountains and started asking the other animals which way to go. The crow pointed north, and the raven pointed south, the deer pointed east, each animal would tell him a different trail they used to get there.

Well to make a very long story short, just you guess who got to the gold first?
You will if you prepare yourself.
Good luck show us the ways your planning and we can discuss the problems along that trail before you begin your trip.


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## cosmetal (Aug 16, 2017)

Butcher,

Absolutely the most spot on, well written and inspiring newbie must-read post I have seen so far! In my opinion, this post should be read by all new and inexperienced members before attempting to “run fast”.

Thank you!
"Starting to trot along" James


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## butcher (Aug 19, 2017)

Here are a few of the must read posts which I find should help out our new members.
http://goldrefiningforum.com/phpBB3/viewforum.php?f=47
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=47&t=1300
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=47&t=3781
http://goldrefiningforum.com/phpBB3/viewforum.php?f=85
http://goldrefiningforum.com/phpBB3/viewtopic.php?t=42
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=70&t=4646
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=33&t=796
http://au-prospecting.com/gr/gr.html
http://goldrefiningforum.com/phpBB3/viewtopic.php?t=562
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=60&t=5604
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=52&t=9349
http://goldrecovery.us/forum_search.asp
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=54&t=19798
http://www.public.asu.edu/~jpbirk/qual/qualanal/catprop.html
http://www.public.asu.edu/~jpbirk/qual/qualanal/confirm.htm
http://www.goldnscrap.com/
http://goldrefiningforum.com/phpBB3/viewtopic.php?p=6873#6873


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## cosmetal (Aug 19, 2017)

Thanks . . . . my "trotting along" continues!

James


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## Wilo (Aug 21, 2017)

butcher, thank you so so much for your explanation. will do from the beginning again and start fresh although it failed it gave me experiences. 
I will continue learning and keep on reading the tutorial. while experiment I will post step by step the process i'll be doing entirely. 
appreciate it so much if everyone can guide me.


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