Problem dropping gold

[Charles Connor]

Good afternoon, i`ve come up with this problem: i was recovering some gold from floor sweeps (did all the magnet and burning) and the SnCl2 test marks positive for gold, so (with AR) by the time i added the SMD, an orange foam forms and floats in the beaker, i`ve had this problem too with vacuum sweeps but the gold test was negative. So i wonder if some of you have also been in this situation and if could solve it. Thanks

 

[FrugalRefiner]

An orange (or brown) foam sounds like you had too much nitric and didn't get it deNOxed. Did you premix your AR based on a ratio, or add nitric in increments? Did you use heat to drive the digestion to completion? After you dissolved everything, did you evaporate to deNOx or add a gold button or any sulfamic acid?

Dave

 

[Charles Connor]

Here`s the thing, i used the same method as i do with the sweeps from a vaccum of jewerly polishing machines, i do not know the ammount of gold in it so i add the nitric until i see no reaction, i dont have a heating plate, also it was 1kilo of dust after burned. Also im like one of the few who uses urea to deNOx, it work every time for me, even the sweeps, its just this thime that the scrap came from the furnace and melting area... what i think is that it may have way too much contaminants and the ammount of gold could be like 2 grams per litre of solution, assuming thats the average from the color with the SnCl2

 

[Pantherlikher]

Here`s the thing, i do not know the ammount of gold in it so i add the nitric until i see no reaction, i dont have a heating plate, also it was 1kilo of dust after burned. Also im like one of the few who uses urea to deNOx, it work every time for me, even the sweeps, ...what i think is that it may have way too much contaminants and the ammount of gold could be like 2 grams per litre of solution, assuming thats the average from the color with the SnCl2

So...what you are saying is you are special... unlike the rest of us in that Urea works for you... but does not in the real world.
You added nitric untill it stopped reacting, without heating. Why do you not need a heating plate but the rest of us do?
You also said based on the color of the test, you have like 2grams/ liter...
Show us where color indicates amounts? please, we could really use this information...

Ok...done insulting you and sorry for that but...

Stop doing things half assed.... learn the whole procedure and follow it completely to insure you do not have problems and if so, you know why and how to fix it without adding to the vastness of the forum.

B.S.
...Again sorry for being harsh...

 

[Charles Connor]

Dont worry gentelman, problem fixed, mjust let it settle for a couple hours... as i have not had any problems refining for a really long time i did not know what happened, in fact this was a new kind of scrap. im not that newbie in this field, im 18 and i already refine Au and Ag 8) and dont worry panther i know how we act when we know how things are done around here... Thanks for your time

 

[FrugalRefiner]

The mix was probably different between the floor sweeps and vacuum sweeps, so your usual procedure was probably off a bit and you overshot the nitric a bit. If it's not too much over, the SMB will just deplete the small excess and the gold will drop. Be sure to test the remaining solution to be sure the reduction is complete. If there was too much excess nitric, you'll end up with some salts mixed with the gold.

Dave

 

[g_axelsson]

You also said based on the color of the test, you have like 2grams/ liter...
Show us where color indicates amounts? please, we could really use this information...

Here it is...
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=49&t=18342#p184831

But I'm pretty sure Hoke mentions it in at least one of her books.

Göran

 

[necromancer]

he fixed it, bet he will not post again until his next problem :!:

 

[nickvc]

When doing sweeps you need heat and agitation to make sure all the values are exposed to the acids, if you haven't used nth I'd bet your material will still have values in them.

 

[Pantherlikher]

I know Göran it is possible to scientifically get a close measure of how much gold is in solution. But based on the question and explanation of what has been done so far, how could it possibly be close to an accuate measurement?

I am assuming his results are based on color of past soutions. Not a measure of the solution in question.

Everything I have read so far about Urea.... leads me to believe that it will not "denox" very well. And adding nitric untill the reaction stops without heat tells me there would be too much free nitric for it to do anything. Except the addition of way to much urea which causes problems. Right? I am asking...

B.S.
...Trying to keep things straight in a foggy mind is very challenging...

 

[g_axelsson]

This is a purely theoretically discussion on urea for denoxing a solution. I have no experience in urea for denoxing since I have never used it and doesn't plan to do it, so don't take my word on it, I wouldn't. This is just my mental picture of what is happening.

As far as I understand, adding urea to nitric acid should work, but not to nitric salts unless you have an acid present.

for example, if I dissolve copper and gold in poor mans AR (nitrate salt + HCl) I would end up with copper nitrate, copper chloride and gold chloride plus the original nitrate salt and HCl. If I would add urea to this I would turn the HCl and nitrate salts into gases and chloride salts, but the reaction would stop when I run out of HCl and people would mistake it for a complete denoxed solution.
What we have now is a micture of more or less of copper nitrate, copper chloride, gold chloride, nitrate and chloride salt from the nitrate we added and small amounts of urea but no HCl or other acid.
Adding SMB to this soup would turn gold chloride into sodium bisulfate and metallic gold.
Sodium bisulfate is acidic and with the chloride and nitrate ions in the solution it will turn the soup into aqua regia again and redissolve the gold.
Even if the left over urea can neutralize the nitric acid that is formed, when the gold powder is washed in HCl some will be redissolved when the dragged down nitric ions reacts with the HCl and forms poor mans AR again.

... and there is also the risk of forming explosive compounds with urea in certain situations.

Let me know if I my theory is just wrong or if there is some truth behind it.

Personally I try to keep the nitric acid usage at a low level so mostly I don't need to denox or I can do it with one evaporation.

Göran

 

[Charles Connor]

these are some formulas that come in the books i learned about the excess of nitric and deNOxing with SMB

 

[butcher]

Urea with nitric acid will convert nitric acid to urea nitrate, a salt of the acid and urea.

Urea can decompose to form ammonia or ammonium compounds in certain reactions.

Both of these can cause problems, or even dangerous solutions with the reactions in recovery or refining of precious metals.

Impurities in a solution of gold chloride, gold dissolved in aqua regia,, like copper, even an almost pure gold chloride solution will have some degree of other metals involved, the amount of these other metals can be a small amount to heavily contaminated with base metals and very little gold, depending on what is in solution.

Urea will not destroy nitric acid.
Urea can destroy the NOx gases in a solution of nitric acid.
Urea can form salts of nitrates with nitric acid.

Metals like copper, or other base metals can form nitrate salts in solution.
Urea will not destroy nitrate salts in solution.

Urea can decompose the NOx gases in nitric acid, or a solution of gold chloride, but it will not destroy free nitric acid or nitrate salts.

If the solution was only gold chloride, with only gold in solution, and no other base metal (almost impossible most of the time), and there was not free nitric acid in solution, then urea would work to decompose the NOx gases.

But if there are other base metals involved, which is always the case and depending on the solution, that is just a matter of how much.

And if there is free nitric acid in solution, depending on solution and how you performed the work, another question of how much.

The Urea may or may not work to De-NOx the solution, it may or may not form ammonium compounds, which could interfere with the PGM metals if they are in solution forming compounds making recovery difficult of the PGM's later, or form urea nitrate or ammonium compounds that can possibly make a dangerous situation in recovery refining or waste treatment...

Much depends on the solution, the free nitric acid involved, the base metals involved and other conditions of the reaction.

Metals in solution can form nitrates, like copper nitrate, with acid like HCl these nitrate salts can again form (a form of) aqua regia which will re-dissolve the gold in solution, even urea nitrate and HCl will dissolve gold.

Basically, I a have a hard time explaining this, and the complications involved in the use of urea in a solution of aqua regia, except to say if conditions of the solution are right it will work, but most of the time you will have too much nitric or base metals that will cause problems, or platinum group metals where urea will cause problems with recovery, and you or are taking a chance of creating an explosive compound when using urea.

Urea is not needed in recovery or refining.

If you need a chemical to de-NOx use sulfamic acid, (which can be found as a grout cleaner to clean grout from ceramic tile, at stores like Home depot), using sulfamic acid which actually has benefits, like making H2SO4 in solution that can help if you are going to evaporate the solution, or to help remove lead from the solution as lead sulfate.

Learn how much nitric to use, and add only the amount needed.

Use Heat to evaporate the solution, to decompose NOx gases and free nitric acid.

Use heat and more gold to de-NOx the solution, consuming the free nitric acid in solution.

Use urea you have as fertilizer, and learn to recover and refine without it, it will be safer, easier and you will have less problems.

 

[joubjonn]

I usually denox with sulfamic. Sometimes I'll use the gold button to eat up very small amounts of extra nitric. Trick is to use as little as possible. Forget about the ratio 1:3 HCl/Nitric. That's not the way we do it here. Sometimes it is difficult to know the exact amount for processes like ceramic cpu's. In that case I won't use a gold button, just a few pinches of sulfamic. And yes SMB is good for denoxing a very small amount of excess nitric.

 

[Charles Connor]

Absolutly i agree with you Butcher, i want to do it as pure as possible the fact is that where i work, they left me a 50 kilo sack of urea and here in costa rica getting chemicals is a matter of a lot of permissions and buying laboratory equipment is really expensive, for example: because of the taxes a heating plate that is $900 in Corning USA, here they sell it for like $1600, so, its like working with what you get, i can get the HNO3, the HCl and the SMB, wich is what i mainly need. In fact where i sell the gold they have it tested every time and it does not goes under .9995, so i wonder if making it without urea would get me those .99999

 

[butcher]

The heating plate can be made from 0r of many different things (if you have a way to cook food) you can get or make a heating plate to give heat to a solution, control of the heat is needed.

Personally I would use the urea for fertilizer.
Even if you cannot get sulfamic acid, you can still work with out it.
There are several methods to choose from, you can also use combinations of these, to get the desired results.

Learn to use acids wisely.
Use heat.
Use gold.

 

[g_axelsson]

I see, the urea doesn't touch nitric acid or nitrates unless there is quite a lot of HCl in the solution.

According to http://en.wikipedia.org/wiki/Aqua_regia#Decomposition_of_aqua_regia
In a first step aqua regia decomposes into nitrosyl chloride and chlorine, then in step 2 the nitrosyl chloride breaks down to nitric oxide and chlorine.
The second step is in equilibrium with nitric oxide and chlorine dissolved in the solution. Urea attacks this equilibrium by removing the nitric oxide and then step 2 transforms more nitrosyl chloride into nitric oxide until the nitrosyl chloride is gone.
This will also consume HCl which is turned into Cl₂(g).

This brings some light to the process of denoxing with evaporation and HCl additions.

When evaporating both HCl and HNO₃ goes off as gases, but when we add HCl to the concentrated hot solution it reacts with the nitric acid, turning it into nitrosyl chloride and then into gases. Since we have heated the solution the resulting gases is quickly expelled and the breakdown of the nitric acid continues.

Basically the heated evaporation - dilution with HCl and urea works based on the same principle, drive the breakdown of aqua regia to the gas state and expel the gases from the solution.

Am I getting close?

Göran

 

[butcher]

Very close, indeed almost spot on.

Actually much of these reactions are over simplified to try to understand what is going on.

In these reaction with metals and the acids many things are going on at once, these equations can help us to understand some of it, but it would be very hard to write an equation or describe all of the reactions happening, and each batch of gold and aqua regia and base metal can be somewhat different, base metals in solution can add to the complexity, base metal can also react with these acids and gases formed in solution, forming base metal chloride salts and base metal nitrate salts, on evaporation we can have nitrate salts, adding a little free HCl to the concentrated solution can again form aqua regia, by reaction of the nitrate salts and HCl, giving us another red cloud of NOx gas as these nitrates decompose, the second evaporation, can help to decompose more of the nitric and NOx gases in solution, and a third evaporation is recommended to completely remove the last possible trace of the free nitric acid.

We have several approaches for this problem.
Evaporation to syrup three times with a small addition of HCl to the concentrated solution between the process.
Leaving undissolved gold, or adding some gold to consume the nitric.
Sulfamic acid to destroy the nitric acid.
Heat can be a very important tool, that should not be overlooked.

We can use one or a combination of these methods to overcome the problem of nitric or nitrates in solution.

I like to use one or many times a combination of these methods, and depending on what I am working on I may use a bit slightly different approach on different batches, first limiting excess HNO3 where you can, I try to calculate how much that may be needed (when I can), measure it out and add it in small increments with heat, giving time for the reaction to complete before adding more nitric acid, and sometimes even leaving a bit of undissolved gold which I will get on the next batch, I can use sulfamic acid to help rid nitric, which also has the benefits mentioned above, then there is adding the button of gold and heat to consume free nitric, and the evaporation process, I like to use combinations of these methods, sometime one or more during the process,I had so much trouble with nitric acid, that I want to be sure I do not have that problem again, and since getting a better understanding, and using combination of these methods to eliminate free nitric from solution, I have not had the problem since.

Free HCl does not cause any problems as long as the nitrates or nitric or NOx gases are not involved to re-dissolve the gold, or to prevent the gold from forming a precipitate.

Not using heat in recovery and refining, to me would be like eating all of your meat raw (it is better cooked), Heat in recovery and refining has many benefits, also well as cold or cooling can have benefits with many things we do, these both can be very important tools to many reactions.

 

[g_axelsson]

Thanks Butcher, you have raised my understanding of the denoxing process another step. 8)

Göran

 

[Pantherlikher]

Thanks to ya'll for a better understanding...

Now to apply everything to costa rica and it's problems getting stuff needed. This can pose a problem which can be solved with alittle research.

Who's sending me plane tickets to costa rica so I can do the on the ground research? Just kidding...

Ok, a heat source. Are you allowed to goto the dump/trash storage area? Do you have coffee there? A coffee maker is great for a heat sorce.

As far as adding nitric acid, do not use the 3:1 ratio. Explained her numerous times as it is too much nitric for the batches we do. I would think it safe to add half of the calculated. Let the reaction stop and then add some heat. Not to boil but to heat. At this point, I would look to determin if all the metals are close to being dissolved. If not, add alittle more and wait with heat. When there is very little but some metal still undissolved, I would stop and process the liquid from here saving what is left for the next reaction. This would eliminate any excess nitric to worry about.

Let us know what you think. And good luck.

B.S.