# evape of excess HN03 add hcl.. no color change



## steyr223 (Oct 7, 2013)

Hello gentleman ladies how's everybody today.

About 2 maybe 3 months ago I did a process with HCL and Pottasium nitrate for my nitre with Assorted ceramic ic's.

I left in container knowing I had used excessive nitre and would need to evape before
Precipitation of Au.
A few days ago I purchased a double burner 
So I could do the long tedious evape

I evaped 800ml to 250ml which in my color blind
Eyes seemed almost black in color (very dark green)

I added HCL back to 800ml witb no color change
I did this again down to 250ml and up to 800ml
Still no color change

I am just curios if anyone else has had this happen
Thanks steyr223 rob


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## steyr223 (Oct 7, 2013)

Sorry i reached the botom

Through this process my stannous tests were
Possative but then my SnCl expired .
my standard AuCl tested negative
And when I opened the primary bottle( I use a dropper bottle)
My SnCl was yellow so I need to make some more

Also need to mention : now tha ti am using fire
instead of electricity I found regulaing my temp to steam
near impossable so I boiled with a watch glass on top
there was no splashing at all

All coments welcome thanks steyr223 rob


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## niteliteone (Oct 7, 2013)

Steyr223,
I believe you need to "evaporate" down a little farther. I understand that it should be almost like syrup (honey) before you add additional HCl. Also it's a good idea to add a few ml of sulfuric acid to help avoid evaporating the solution dry. That's the way I learned and do myself.


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## steyr223 (Oct 7, 2013)

Thanks for the quick reply niteliteon
I thought that maybe if I evaped more it
Might take out more of whatever is causing the
Dark color
I also added some sulfumic acid to percipitate the
Led 
Thanks I will try
Steyr223 rob


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## Geo (Oct 7, 2013)

guys, go back to Hoke's book and check the section on ridding excess nitric. evaporating to a syrup and then adding hcl again does not rid the solution of free nitric. you are only evaporating and re-hydrating. you must add sulfuric acid to the solution before evaporating for the free nitric to be expelled. 
Hoke's book : (5) REMOVING EXCESS NITRIC ACID
You were told to use no more aqua regia than was required. Be-ginners always use too much. Experienced workers often do the same thing, especially when in a hurry, because fresh acids work more rapidly than those that are partly exhausted.Sooner or later you must get rid of the unused nitric acid. Most workers think it pays to do so right away, as followsut the aqua regia solution into a big evaporating dish. It will contain some sediment, mostly silver chloride; this does no harm at this point, so do not filter it yet. Now add a little sulphuric acid,stirring all the time, and working slowly, as it might spatter. Use about an ounce or less of the sulphuric acid to each quart of liquid. Now boil the solution down gently, to a syrup, being careful not to spatter. The purpose of the sulphuric acid will be explained later.This evaporation is a tiresome process. It goes rapidly at first, but soon the liquid begins to spatter and you must lower the flame. Do not cover the dish, as that merely impedes evaporation. A sand bath or a steam bath is useful; these have already been described.When using a sand bath, start work by pushing the sand to the sides of the pan, so that the heat can quickly reach the evaporating dish; later, as evaporation has progressed, scrape the sand down underneath the dish, to lessen the tendency to spatter.The advantage of the steam hath is that it does not cause spatter-ing, and a dish can be left on it without supervision, without danger of overheating.Let the evaporation continue until the liquid becomes syrupy;then slowly add a little full-strength hydrochloric acid. Brown fumes will bubble off; this is the unused nitric acid being expelled.Usually this evaporation must be repeated at least once, maybe twice evaporating to a syrup and adding a little hydrochloric acid in order to get rid of all the unused nitric acid.


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## FrugalRefiner (Oct 7, 2013)

Geo,

While I agree that a small amount of sulfuric acid is _helpful_ during evaporation, it is not absolutely essential. Evaporating to a syrup is tricky, as it's very easy to overshoot. If you don't evaporate far enough, you don't accomplish your purpose. If you evaporate too much, you can end up with an undesirable crust. Once you have the solution to the consistency you want, it's still very hot, and it will continue to evaporate beyond the point you want as the nitric and hydrochloric acids will both evaporate entirely at these temperatures. This is where that bit of sulfuric can save the day, as it will not evaporate until it reaches much higher temperatures, so even if you carry the process too far, the sulfuric acid will still remain as a small amount of solution.

It is entirely possible to eliminate the excess nitric through evaporation without the sulfuric. It's just trickier. At least, that's how I understand it.

Dave


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## Geo (Oct 7, 2013)

i believe in working smarter and not harder. why make an already difficult process even more difficult. ive only tried the method twice and it seemed to work fine both times. i also believe that if something isnt broke, dont fix it.


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## butcher (Oct 7, 2013)

Heating the solution will form vapors, since water is a part of the acids,and the reaction, water vapors of first, as it is more volatile, the nitric will concentrate with the HCl in solution, then as it concentrates the nitric acid will begin to vapor off in the fumes and will begin to come off as vapors of Nox gases, free HCl will then concentrate more and free HCl will hydrogen chloride gas will vapor off, these gases will not be pure as there is some overlap of the gases that escape, but this is the order of volatility, a tiny bit of sulfuric acid is used for two reasons it will not boil off and will stay in solution with the heated salts preventing them from being baked dry, if evaporation carried too far by mistake, it will also be useful to form lead sulfate which will precipitate later with dilution.

As gold salts concentrate the solution can change from a yellow to solution to more of an orange solution, and of coarse if base metals are involved the color of the solution will reflect those metals, copper is a metal that gives strong color to solutions.

Free acid vapors off fairly easy at the proper temperature and concentration of solution.


Because the free nitric usually will not come off at the first evaporation, although most of the free nitric acid will, some may remain after the first evaporation, another reason is the nitric acid can form nitrate salts with metals, example copper nitrate, and during evaporation these nitrate salts can crystallize remaining with the gold when adding Acid to re-wet these nitrate salts will take hydrogen from the acid, reforming HNO3 again, this can be seen when acid is added to the concentrated solution a plume of Nox gas will usually evolve, the added acid (usually HCl) contains water which will also dilute these salts of gold chloride, this volume of added acid in normally very small so the work of evaporation a second time does not take that long, again we evaporate the nitric formed in solution, repeating the process a third time will normally eliminate the nitric from solution, leaving us with a gold chloride solution, and depending on on our previous work only a little other metal chlorides in solution.

But salts of metals do not lose their acid anion easily at the temperatures we evaporate the free acids from solution, these metal salts like gold chloride or copper nitrate can be crystallized, you could evaporate the copper nitrate salt to a dry state and it will not eliminate the nitrate anion, copper nitrate has to be heated at very high temperature before it will release this nitrate Anion as NO2 gas and form copper oxide.

So if we have nitrate salts with our gold chloride salts re-wetting with acid keeps the gold dissolved when we go and try to precipitate the gold from this solution, and can also give us trouble determining gold is in solution with our stannous chloride testing procedures.

With poor mans aqua regia there can be more trouble to evaporate the nitric or getting rid of the nitrate salts from solution, especially if more base metals like copper are involved, which is usually the case, as in the evaporation process copper nitrate can be formed, the copper nitrate can be baked dry with the gold salts, (evaporation does not eliminate them), re-wetting the copper nitrate salts with acid, easily forms nitric acid again in solution, so an excess of nitrate salts when using poor mans aqua regia will give more trouble to eliminate the oxidizer, (nitrates and nitric), than you would have when using nitric acid with real aqua regia (and also where we normally eliminate most of the base metals as possible before dissolving our gold).


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## niteliteone (Oct 7, 2013)

I remember reading in Hokes book that the sulfuric was to help Not to evaporate too much, as it was easy to over shoot the evaporation "past" syrup.
I could be mistaken, but I'm pretty sure this was the "why" to add sulfuric to the mix.
I guess it's time for my yearly reading of Hokes book. 8)

Butcher,
Thanks for the explanation you posted (while I was writing my reply) You explained what I remembered much better than my memory would put words to. :shock: 
Thank You.


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## moose7802 (Oct 7, 2013)

Quick question a little off topic. Could I add a little sulfuric acid to my water when washing my Au powder as to not let it dry out on accident when boiling for a long time? Or would this cause a problem when melting later on?


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## Pantherlikher (Oct 7, 2013)

Hoke's book. 
I just reread this entire part...
GO READ...


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## Harold_V (Oct 7, 2013)

The advice to read Hoke's book is quite good, but if you'd like my opinion, I wouldn't add sulfuric. It won't be easy to eliminate fully, even with a boiling rinse, so melting the resulting gold could prove to be less than fun. 

Washing gold can be tricky. On many occasions I experienced bumping, and nothing I did would eliminate the problem. The bumping results in severe splashing, and can even be the source of a beaker flying off the hot plate. I broke more than one beaker that way in my many years of refining. 

My advice to you is to wash your gold with your full attention. There is no reason for it to run dry if you're there with it. Setting it to wash and leaving can be risky. 

Harold


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## moose7802 (Oct 8, 2013)

I'm sorry to bother, I did read the section just wanted to ask about personal experiences. Thanks Harold that has been how I have done it thus far, by watching it and will continue to. Just thought I would see if anyone has done this and there results.


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## butcher (Oct 8, 2013)

The process of washing the gold powders is different than when we are evaporating the gold chloride to concentrate it to expel excess nitric acid where adding a few ml of H2SO4 can be helpful if we make a mistake and evaporate too far.

In the gold wash procedure I do not attempt to evaporate off the acids.

When washing the gold powders I have never had a problem of evaporating to dryness by mistake.

I use the gold washing procedure described by Harold (Harold's classic gold washing technique) found in the thread getting your gold pure and shining, as it seems the best way to get rid of the metal contaminates that can be washed out, It is very close to the gold wash technique Hoke recommends on page 47, but she does not mention the ammonia cycle (which can help to wash out silver chloride traces), I always use a dilute HCl wash afterwards just for safety.

Hoke book also mentions some refiners use a two acid wash, on page 61, sometimes sulfuric acid is used before one of the HCl washes, here the gold is covered in cold water and a few drops of H2SO4 is carefully added slowly and stirred well. (Do not add water to concentrated sulfuric acid.) 
Working slowly or it may spatter.
This is then heated to boiling, then wash well with plain water to remove the acid, then the normal wash cycle with HCl and so on is done as normal (described on page 47).

I have not tried this procedure using the dilute sulfuric acid wash, and I am unsure of what benefit it would provide if any.(Since most of us refine a lot of electronic scrap where lead can be a problem, I feel if sulfuric was added before all of lead salts were washed out from the gold powders as lead chlorides (using the boiling hot water wash cycles), my fear is the lead would form an insoluble lead sulfate that will not wash out from the gold powders.


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## niteliteone (Oct 8, 2013)

For those that come across this thread and wonder why the mixed messages...
This thread started with a question about evaporating a "poormans" AR solution and half way through the thread "Moose" ask a question on washing gold powders, giving a slightly confusing turn people need to see and understand.

All is normal here :lol: , people just need to realize we are talking about 2 different processes in a single thread.
Hope that helps avoid confusion at a later date.


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## moose7802 (Oct 8, 2013)

Sorry about the mixing on this thread or any confusion, just made me think about what would. Butcher that's kind of what I was thinking and why I asked the question, thinking that lead would maybe come back out if sulfuric acid was added before the powder was totally washed.


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## niteliteone (Oct 8, 2013)

No problem Moose, it happens quite often here on GRF. I just posted the notice of the 2 topics, so later others will understand what we are talking about, since the transition is easy to miss, especially for a newbie.


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## freechemist (Oct 8, 2013)

Adding a sufficient amount of sulfuric acid to mixtures to be evaporated for getting rid of free HNO3 helps to attain temperatures high enough, to allow HNO3-(and HCl-)vapours to escape, keeping the mixture in a mostly liquid state. It also dissolves/decomposes eventually formed solid base-metal nitrates and chlorides to hydrogensulfates and the much more volatile free acids HNO3 and HCl.


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## steyr223 (Oct 10, 2013)

Thanks again for your comments
I would love to try all this one more time
But since this batch I have learned to not
add to much nitre. 8) 

Harold bumbing?
I experienced only once when I was steaming
My solution to free nitric, it didn't start untill
Almost 16 hrs on the electric hot plate in a coffe
pot( the older kind that you actually made coffe in
All glass even perculator)
All of a sudden the top would jump up and hit the little
Tabs kepping it on but very close to breaking
From what I read about this they were called steam
Explotions . Is this the same thing you call bumbing?
Thanks everybody steyr223 rob


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## steyr223 (Oct 10, 2013)

Free chemist what's up
question you said adding sulfuric will attain higher
Temps which is understood since it boil way hotter
But
if you were to just steam to evape would it still attain
Higher temps?

I didn't think gold could be trapped in metal salts
after washing some of my salts the other day and
Explaining to a friend that everything on earth is some
How related to salt I ....um..tasted some :shock: 
To my amazement it was salt every day table salt
I hope i didn't eat my gold 
***PLEASE DONT EAT YOUR SALTS OR GOLD AS IT COULD
BE HAZARDOUS TO YOUR HEALTH***
thanks steyr223 rob


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## butcher (Oct 10, 2013)

Actually gold chloride is a salt of gold, the gold we see dissolved in that yellow solution could be evaporated to crystals of gold salts.

Metal + Acid = salt of that metal.
Example:
Copper + HNO3 --> copper nitrate salt {dissolved in a solution, the cation copper ions, the anion nitrate ions}

The solution or salt could be high in NaCl depending on the process, and taste like table salt, but you could have other base metal chlorides involved depending on the source, many of which can be poisonous, and may not taste much different from the salt, not a good idea to be tasting.
An old method of testing an unknown was touching a dab to the tongue, acid would bite the tongue, but nowadays we have much better testing methods, and more common sense than to be tasting our solutions.


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## Esau Nisalile (Oct 10, 2013)

I was using evaporation as a denox process until when I read somewhere hear with controlled nitrate additions during gold dissolution, then at the end add urea until no fissing. It works very fine and I was served from that tedious evaporating process.I use that everytime and get instant drop with Smb. So fot your case if you have urea at hand which is normal fertilizer toss 5 to 6 pellets into your solution and watch if no fissing then be sure no free nitrates from which you can proceed to dropping. I can't explain in detail the chemistry behind but after I read from here tested and it works, serves labour and time.
Regards,
Esau


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## Geo (Oct 10, 2013)

even though the use of urea is commonly accepted and widely used, its normally not recommended because it just adds another chemical to the mix. if you follow good work habits when putting metals into solution, you shouldnt have to remove free nitric in the first place.


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## butcher (Oct 10, 2013)

Esau Nisalile,
Urea is not a good idea, in my opinion, actually a very bad idea, as far as I am concerned, it can add contaminates, it can form ammonium nitrate (an explosive mix) which under some conditions could be very dangerous (especially with heated glassware being so close to our face, the urea can also form ammine in solutions the ammine compounds can complicate platinum group recovery (if involved).

Sulfamic acid will work better if needed, as its byproduct is sulfuric acid which has the benefit in solution (can help when evaporating to keep from forming salts if the process carried too far), (and will precipitate lead from solution as an insoluble lead sulfate), sulfamic acid can be found as a grout cleaner for tile grout (found in the flooring section of the hardware store near where I live).

Harold's trick of adding a button of gold to use up excess nitric acid, with heating, is a great way to remove excess HNO3 from solution.

Knowing How much acids to use for each gram or ounce of gold, and adding the nitric measured in small increments, using heat to drive the reaction and dissolve the gold, using up the added HNO3 before adding a bit more to insure excess nitric is consumed in the reaction, is the first step to not using too much nitric or having to eliminate it later in the process.

Leaving a little bit of undissolved gold behind in the reaction (works similar to Harold's method above), this little bit of gold can be added to the next refining process.

4 fl. Oz. of 32% HCl and 1 fl. Oz of 70% HNO3 will dissolve a troy ounce of gold (31.103 g Au).
Using the formula above from Hoke's book we can figure from this:
118.29 ml HCl + 29.57 ml HNO3 per Troy Oz of gold.
3.8 ml of HCl and 0.95 ml HNO3 per gram of gold

With this, lets say I have 10 grams of gold powders recovered and I wish to refine them, I can cover them with 38 ml of HCl (I may add just a bit more no harm), set this on a mild heat, then measure out 9.5 ml HNO3 in a clean vessel, using a pipette I can add only a few milliliters of HNO3 at a time, waiting for the reaction to complete before adding more, heating the solution also speeds the reaction, but also concentrates the acid, as it evaporates the water added (involved in acids and the water produced from the reaction), this is actually concentrating and evaporating my solution as I work, we just do not want to heat too hard, or we could vapor off the needed HCl in solution. We may not need all of the measured nitric to dissolve our gold.

At this point after the gold has reacted, we can leave a bit of the gold undissolved for the next batch, or add a gold button to consume any free HNO3 (if we used more than needed), we can continue to concentrate the solution through evaporation, getting the solution concentrated, (here we normally add a few drops of H2SO4) but we can add a little sulfamic acid for the same purpose, which will also work to eliminate free HNO3, after concentrating we can cool the solution down with three to four volumes of water, let it sit overnight to precipitate silver chloride and lead sulfate..., and filter the clear bright yellow decanted solution before precipitating the gold with our choice of chemical precipitant.

Although not all of these methods are needed to eliminate free HNO3, using a combination of them for me insures I do not have problems with precipitating the gold, because of excess nitric in solution.

A trick I use is the stannous chloride test of the gold solution before precipitating gold, getting a positive purple of Cassius reaction, lets me know the stannous chloride can reduce the gold to metal colloids, this is a good indicator free nitric acid has been eliminated from the gold chloride solution, and thus my chemical precipitant (such as sodium metabisulfite) should not have problems reducing the gold ionic salts back to elemental metal gold powders and precipitate my gold.


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## goldsilverpro (Oct 10, 2013)

butcher said:


> A trick I use is the stannous chloride test of the gold solution before precipitating gold, getting a positive purple of Cassius reaction, lets me know the stannous chloride can reduce the gold to metal colloids, this is a good indicator free nitric acid has been eliminated from the gold chloride solution, and thus my chemical precipitant (such as sodium metabisulfite) should not have problems reducing the gold ionic salts back to elemental metal gold powders and precipitate my gold.



Sorry Richard, but I just can't agree with that. Recently, I mentioned that one of my gold dissolving processes used a solution of 50% (v/v) nitric plus water and a little HCl. After precipitating the gold, I tested for gold in a spot plate with stannous chloride. I used 1 drop of sample and 1 drop of SnCl2. The purple/black appeared immediately but then quickly disappeared. To a clean cavity on the spot plate, I then added a drop of sample, 4 or 5 drops of water, and a drop of SnCl2. This time, the color formed and lasted for a very long time - hours, maybe. The free nitric was still there but it was diluted to about 5 - 10%. In the dissolving of the gold in this case, very little nitric was consumed, 2 or 3%, maybe. I did this test on that material 100s of times. Try it.


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## moose7802 (Oct 10, 2013)

I have run maybe only 6lbs of ceramic cpus using poor man's AR and I have never had to add urea, I don't even have any on property. Jeff has given me the best advise when I started and that was to just add small additions of the nitrate and wait till exhausted. By doing the process this way I have never had to use urea and don't think I ever want to. Thanks again to all the members here you have made my short time of refining great and now will be a hobby of mine forever. I have gold fever!!


Thanks
Tyler


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## Harold_V (Oct 10, 2013)

moose7802 said:


> I have run maybe only 6lbs of ceramic cpus using poor man's AR and I have never had to add urea, I don't even have any on property. Jeff has given me the best advise when I started and that was to just add small additions of the nitrate and wait till exhausted. By doing the process this way I have never had to use urea and don't think I ever want to.


For the record, the concept of adding nitric in small quantities has been promoted from the outset by GSP. It's a wise method of limiting free nitric, but isn't always the best solution to the problem, depending on the nature of the material being processed. I offer you, as an example, filings from the jeweler's bench. They typically contain substances that do not dissolve (often abrasive bits), and are not easily discerned from filings, so to guarantee that all of the gold is recovered from such material, a slight excess of nitric is desirable, as it ensures that you leave nothing of value behind. 

In instances such as this, evaporating to eliminate the free nitric isn't necessary, assuming you're willing to add a button of gold to consume the unused nitric. It's the best of all worlds. 

In all of my refining career, which lasted more than 20 years, urea was NEVER used. 

Harold


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## butcher (Oct 10, 2013)

Thank you GSP, I will do some more getting acquainted experiments with various additions of HNO3 to a gold chloride solution and testing with Stannous chloride, to get more familiar with that reaction, and how of various amounts of nitric or or dilution effects this test.

I have noticed before with small amounts of free nitric in solution the immediate violet reaction disappear as the gold was re-oxidized back into solution, and I have also noticed with more nitric in solution the stannous chloride would not show a reaction even with gold in solution.


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## moose7802 (Oct 10, 2013)

Harold I keep a few grams of dried gold flakes from some fingers and I always drop 1or 2 in to see if they dissolve. Now I know there are BMs in these flakes but the small amount I add will be nothing that isn't washed out at the end. Like I said maybe 1 or 2 flakes from some fingers just to see if there is free nitric. So I guess you could say I kind of do what what has been mentioned here. Now that I have melted my second button though, I am going to use that from now on to use up any free nitric.

Tyler


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## goldsilverpro (Oct 11, 2013)

I have used the incremental additions of nitric method for more than 30 years and I introduced it to the forum in the early days, as Harold said. I kept pushing it and it took about a year before it finally caught on. I think Lazersteve was the first to adopt it. Now, most people on the forum use it. 

When using this method, although I am careful, I probably always end up using a little extra nitric and I believe that anyone using the method will also end up with a little free nitric in the solution. I don't worry about this because I know that it will be eliminated by the sodium sulfite or SMB (I prefer the sodium sulfite, but the SMB is slightly stronger). To eliminate 1 ml of 70% nitric, it takes about 1.5g of SMB, or a little less, if I remember right (that's 3.3 pounds of SMB per liter of nitric). However, if you try to neutralize too much nitric with the SMB or sodium sulfite, there will likely be reaction-products and solubility problems and undesirable crystals can form. Please note that it doesn't take very much to be "too much." The use of SO2 gas will reduce these problems somewhat and allow a greater amount of free nitric to be present.


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## moose7802 (Oct 11, 2013)

Thank you GSP for all your contributions! I have also always felt that way that there has got to be a little free nitric just simply because what are the chances it is totally used up and all metals are in solution. Seems to me that you would have to have a little extra or not enough and we all know not enough is no good. I always add a little extra SMB to make sure that the free nitric would be used up as the gold would drop then go back into solution and drop again until it's used up. But as stated earlier by following your method there is very little free nitric so one addition of SMB is all I have ever had to do.


Thanks
Tyler


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## g_axelsson (Oct 11, 2013)

Since the reaction of nitric acid produces NOx that can be oxidized and reabsorbed in the solution it is really hard to give an exact amount of nitric to use. I dissolved 50+ grams of gold a couple of months ago, I started with all the 150 ml HCl needed but only half of the nitric needed (25 ml). The temp was a bit low around 10C, doing it outside, but without any reflux... almost all gold dissolved. In the end I heated the solution below boiling until I could see no additional reaction. I poured off the gold chloride and added new fresh HCl and a little bit of HNO3 t dissolve the last part.
In the end I had dissolved 50-53 g of gold in 28 ml HNO3 and 170 ml HCl. I now have 200 ml beautiful orange solution (water added during filtration).
I will add some water to precipitate silver chloride and then filtering it again before final drop.

I was very surprised of how little nitric acid I needed, the slow process and cold weather must have reabsorbed the nitric oxides.

When coming to the end of dissolving some gold, the acids are very weak, diluted in a lot of liquid and the surface area of the gold left is a lot smaller. Then it can be faster to pour off what you have and just add small amounts of fresh acids. The strength goes up and there is less of a risk of adding too much acid.

Göran


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## steyr223 (Oct 11, 2013)

Hello
thanks gsp,harold,butcher

I have also never used urea
With poor mans A/R it is a little more difficilt
I use potassium nitrate as my nitre

This all came from a few months ago
I do not add to much nitre now

For the record I have dropped gold when stanmous
showed no color at all
And I have still a solution of beautifull golden yellow
That turns purple instantly but has no gold( I just can't
Seem to get rid of it) :lol: 

Goran that's the same method I have been using
Thanks steyr223 rob


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