# Precipitating Gold



## NobleMetalsRecovery (Dec 16, 2008)

I read today that you can use sulfuric acid to drop gold out of AR. I think you would add it during the last boiling down the solution to rid it of Noxx. The sulfuric acid decomposes and releases SO2 and SO3. SO2 will drop the gold, that's what's released from sodium metabisulfite.

Seems like it would work also with HCL/bleach or HCL/H2O2. just add it and boil it down. 

It's too cold, and wet, and windy to do this in VA, maybe someone else can give it a try.


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## qst42know (Dec 16, 2008)

Where did you read this?

I use a bit in my AR when there is a possibility of lead and as an aid for de-noxing, as Hoke recommends. I have not experienced gold dropping because of it.


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## butcher (Dec 16, 2008)

from what I undertand its used to help rid nitric from aqua regia (also to precipitate lead as sulfite ) also helpful for keeping the solution from crystalizing out salts, 
when ridding nitric acid from Aqua regia solutions evaporation techniques, not sure there would be any appreciable sulfur dioxide generated from it.
not positive. i also believe hokes book mentions this technique. I have not heard of it as precipitant unless when used to make ferrous sulfate, or in SO2 generation and so on.
also the man from mexico (Juan?)who is really good on silver answered a question of a problem where chocolate solution of gold having trouble precipitating from solution, adding sulfuric helps (probably from not eliminating nitric from solution?) but my thoughts were that it was the acid that helped here.


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## NobleMetalsRecovery (Dec 16, 2008)

I'm not sure, my library of Gold related books is about 100 different titles. Once I find it again, I'll let you know.

The key point is that you'd have to boil it to the point where the sulfuric acid decomposes. So normally it wouldn't happen.


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## butcher (Dec 16, 2008)

as the concentration increases so does the boiling point of the sulfuric acid, so before much sulfuric to boil off you would have to get over 600 degrees F or so, or boiling to 98% concentration before much of any SO2 released (maybe memory or a misunderstanding?).


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## NobleMetalsRecovery (Dec 16, 2008)

I found it. The book is "Gold, Recovery, Properties, and Applications. Edmund M. Wise. 1964. page 174.

"Dissolve the gold residue in aqua regia, adding sulfuric acid, filtering, and boiling to S02 fumes. Finely-divided gold remains."


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## NobleMetalsRecovery (Dec 16, 2008)

butcher said:


> as the concentration increases so does the boiling point of the sulfuric acid, so before much sulfuric to boil off you would have to get over 600 degrees F or so, or boiling to 98% concentration before much of any SO2 released (maybe memory or a misunderstanding?).



I found some pictures today on the internet of someone making concentrated sulfuric acid out of battery acid. They boil it down to 25% of the original volume. But, they caution you to do it outdoors because it's releasing SO2 fumes the whole time while it is getting more concentrated.

So I don't think you would need to boil down all the way.


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## NobleMetalsRecovery (Dec 16, 2008)

http://amazingrust.com/Experiments/how_to/Concentrating_H2SO4.html


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## qst42know (Dec 16, 2008)

Having only worked with poor mans Ar and occasionally boiled to only the beginnings of dryness I suspect the gold remaining would be found in a quantity of salts. 

When I have over cooked my solution and it had began to crystallize I re-hydrated the salts with HCL and dropped with SMB. I don't know what the end result would have been if I continued to heat to completely dry.

I would be interested in hearing what one of the chemists on the forum have to say of this technique.


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## Platdigger (Dec 17, 2008)

Sounds similar to boiling a mix of metals in concentrated sulfuric, were nearly every metal will disolve except for gold.
Randy


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## butcher (Dec 17, 2008)

SO2 will boil off after sulfuric in solution is 98%, as white fumes, and you could boil dry and have a gold salt solution,and salts of every thing else in solution, but would not be pure. to me that would kind of defeat my purpose,of using Aqua regia. was this a recovery process, or refining process? either way I would not use it.


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## butcher (Dec 17, 2008)

when boiling sulfuric to concentrate mostly water bois off first (yes very little SO2 will) untill you get to concentrated azeotrope 98% then the SO2 boils out with very little water vapors, this azeotrope is why we can boil weak sulfuric to concentrate it, if SO2 boiled out early at low concentrations we could not concentrate it to 98%.
nitric Acid has an Azeotrope of 68% so if boiling from weak solution, mostly water boils off very little NOx untill we get to 68% concentration that is as concentrated as we can get it then the water and acid boil off at 68% till dry.
check out a chart of sufuric acid concentration and its boiling point temperatures.


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## LittleJohnnyH2SO4 (Dec 23, 2008)

The white fumes from boiling concentrated H2SO4 are SO3, not SO2. (small amounts will decompose to SO2). This is sulfuric anhydride, sulfur trioxide. Horrible awful stuff and it looks white because it's sucking moisture out of the air forming tiny droplets of H2SO4. Also horrible, awful stuff. I don't think I need to explain what a 550F splash of water-hungry concentrated acid would do to any skin, eyes, or for that matter, anything it touches.

It is much more likely that the AuCl3 is being decomposed by the high temperatures and the formed chlorine gas is driven off by the heat. It looks like gold chloride decomposes 40C under the boiling point of sulfuric acid, and the higher temperature would make it go even faster.


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## arthur kierski (Dec 23, 2008)

i bought a book (from a brazillian professor who purify pm for more then 20years) who says ---if you make a fine powder from your alloys and them heat in ar for 10minutes, all the gold goes into solution --add twice the volume of water to the initial ar, filtrate and to the filtrate add more 8 times the volume of the original ar solution---example=100 cc of ar,dilute to 1liter---300ccar to 3liters----then you add to this dilute ar smb,mix until the solution becomes brown and wait till the gold goes down----------------one does not need to add urea or heat the ar 3times to eliminate the hno3---------------
i did this experiment yesterday and tested the solution after filtrating the gold out with stanous chloride ,and it did not indicate any gold--in other words---it worked
any member of this forum can make this experiment and reach its own conclusions-----for me it worked


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## NobleMetalsRecovery (Dec 23, 2008)

arthur kierski said:


> i bought a book (from a brazillian professor who purify pm for more then 20years) who says ---if you make a fine powder from your alloys and them heat in ar for 10minutes, all the gold goes into solution



It makes good sense that this would work. You do not mention what amount of AR is used compared to the amount of alloy. If you have just enough AR all the nitric will be used up. Actually its hard to get the exact amount of AR to dissolve all the alloy so you try to use just a tiny bit more than is needed. That way you will dissolve all the alloy and have very little nitric left in the AR solution. 

By diluting the solution to such a large degree, it greatly weakens the remaining nitric in the AR solution. So the SMB can drop the gold. You should probably filter it as soon as it all drops. If you still have some nitric left in solution, it would be able to slowy begin to redissolve the precipitated gold.


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## arthur kierski (Dec 23, 2008)

he gives an example100grams ---containing;55grams of gold,20grams of silver,15grams of palladium and10grams of copper----he uses 3times the ar,that is225ml of hcl and 75m ml of hno3----all the metals dissolve in 10minutes---he adds 1litre of water,filtrate and to the filtrate add another 1700ml of water to complete 3liters(ten times)-------them ads smb and stir the solution----- with incinerated ash containing lets say 50 grams of gold he does a bit diferent---first hcl wash,(1kilo of ash) them 500ml of ar 4to1 at 50centigrades for 1hour --then a quick boil of the ar,add1.5 liters of water and filtrate---- in the filter he adds 4 times 500ml of hot water to complete 4liters of all and then smb---note:i am passing his way---if one is interested,i sugest that he does the experiment-----for me it is important because i have dificulty with urea(never know whem the addition is sufficient) and also i do not like to evaporate many liters of ar to get rid of hno3----- this is specially writen to nobel metals recovery who asked for quantities of ar in the process---


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## goldsilverpro (Dec 23, 2008)

How do you "powder" the alloy? With 20% silver in his alloy, I can't see it dissolving quickly (or, if at all) in AR unless it were truly powder.


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## arthur kierski (Dec 23, 2008)

here we have a shreder(a machine that triturates the alloys ) which makes a powder less then 0,1mm---this machine is made by a firm called ----hidrometal--------and in the book there is a plan of this machine--pity i cant show you --i do not knoww how to make a picture and pass to the forum


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## qst42know (Dec 23, 2008)

I think I would rather remove the nitric than deal with 10 times the volume of waste. 

By ignoring any remaining nitric and diluting a surplus of SMB could consume the remaining nitric by forcing it to redissolve the first precipitated gold however the partially dissolved gold crystals that dropped first may be very fine and lost through the filter.

If you used Sulfuric acid and boiled until the gold dropped from your AR your starting material would need to be 100% free of lead

While these methods seem plausible, to me they have drawbacks that can be avoided.


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## Platdigger (Dec 23, 2008)

Why not forget AR entirely (for this aplication of finely devided metals), by just using nitric to take up the silver, palladium, and copper, and then HCL/CL for the gold?
Randy


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## goldsilverpro (Dec 23, 2008)

A particle size of .1mm is still of a fairly large size. I would still doubt that AR would dissolve all the gold in the presence of 20% silver. I assume that what you processed didn't have that high of a silver content. And, of course, very few people have access to that type of a shredder. How did the professor produce the required fine powder?


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## arthur kierski (Dec 23, 2008)

i did not ask anyone to use the professors method---i just passed the experience ---with me it worked---i did with cpu processors and extracted 7grams of gold from 1kilo ,which made me very happy----before this professor, my yealds were 5 to 6 grams and i knew that i lost gold in ar----
i got 7grams only when i used cianide and with a method of adding to ar naoh to make hidroxides and then adding hcl to the hidroxides to make chlorides and them any reducing agent to get the gold


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## butcher (Dec 23, 2008)

There are many different ways to process and it can be hard to keep up with, so if a process may work for someone in certain circumstance, can not give good results consistantly or confuse newcomers, will be hard to convince us its better than proven methods.


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## qst42know (Dec 23, 2008)

Elements are almost never lost only misplaced. 

I have gone back to my stock pot more times than I like to admit to recover values. :wink: :wink:

There is no better advice than to save everything till you are certain you recovered all.


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## EVO-AU (Jan 2, 2009)

Gentlemen ( and ladies ):

Anybody try using sodium hydroxide for a precip'er to about Ph5.0 ? It neutralizes the nitric and in some instances, serves to frop the gold as well. Works for me. Evo

Happy New Year Randy !!!!!!!


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## arthur kierski (Jan 2, 2009)

evo--it works for me too but slightly diferrent----naoh till ph 7-8-----forming a ppt,filtering the ppt and adding to it hcl and then ppt the gold with smb----another way is filtering the ppt and adding to it h20 +h2o2----also this way gold is formed------i learned this in a book called qualitative analyses --by VOGUEL-----------------------------------------


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## Platdigger (Jan 2, 2009)

Happy New Year to you too Evo, Thanks!

Now I am sure we both want to know about this water plus h2O2.

Arthur, does the gold form a precip this way?

Perhaps other metals in solution are oxidized, except for gold....?
Randy


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## arthur kierski (Jan 2, 2009)

i knew that you randy would ask----yes the h2o2 oxidizes the other metals which stays in solution and a beautifull light brown gold powder appears as the precipitate-----you have to add water to the ppts from naoh and then add carefullyh2o2(i use 30%) drop by drop until a violent reaction happens and the gold appears as a ppt---i use a big becker because if not the solution might spill


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## goldsilverpro (Jan 2, 2009)

In one of my qualitative analysis books, it says that a gold mirror forms on the glass (they were using a test tube) when using the H2O2. Did you have the same problem?


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## Platdigger (Jan 2, 2009)

I just did a search for this book.......does 93 dollars for a copy of the 7th edition seem like a good price?
Randy


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## arthur kierski (Jan 2, 2009)

randy,i have this book since i became a chemist(many years ago) and its specialty is metals divided in groups--there is a small chapter on pt, pd and au-
the formation of a mirror in the test tube or becker happens often----this mirror formation appears more when one precipitates pd or pt from chlorides solutions with hidrazine---


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## lazersteve (Jan 3, 2009)

Arthur,

Purely accidentally I found that my HCl-Cl leaches from catalytic honeycombs formed a mirror on the plastic reaction vessel walls when diluted with tap water in direct sunlight. This may have been due to hydrogen absorbed by the jug during the leach process, I'm not really sure why it happened, but it did in three different jugs.

Here's how the jugs look before (left) and after (right):

[img:1676:1366]http://www.goldrecovery.us/images/pt_mirror.jpg[/img]

Notice the distinct mirror effect of the jug on the right compared to the one on the left.

Steve


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## NobleMetalsRecovery (Jan 3, 2009)

I've had that happen a lot with gold. It forms a thin gold plating. With gold you can look through it and if it looks green you know it's gold.

How about checking the "film" with an ohm meter to see if it's metallic, i.e. conducts electricity.


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## Harold_V (Jan 4, 2009)

Noble Metals Recovery said:


> I've had that happen a lot with gold. It forms a thin gold plating. With gold you can look through it and if it looks green you know it's gold.
> 
> How about checking the "film" with an ohm meter to see if it's metallic, i.e. conducts electricity.


No need to test. In the first instance, it's gold, the result of using dirty glassware. Your containers must be washed until free of traces of base metals. It doesn't happen when the glassware is perfectly clean. 

Harold


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## NobleMetalsRecovery (Jan 4, 2009)

why not test? Maybe something in the plastic caused some PGM's to precipitate?


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## Harold_V (Jan 4, 2009)

For starters, testing wouldn't provide the least bit of evidence if the plastic was responsible, or not. It's no different than looking at the horizon and concluding that there must be a creator. Looking at the horizon proves there is a horizon, nothing more. 

Regardless of why it's there, it's obviously not a good idea to use plastic, particularly if high values are involved. I've been through that process with cemented silver----and recovered the film by incinerating the plastic. Not a good idea in the scheme of things when the problem can be avoided. 

My point was directed to gold----likely misdirected in this case. Still, a film such as you described is almost guaranteed to be metallic in nature, and conductive. I can think of no other reason for a metallic appearing film to be created under like circumstances. Why it deposited on plastic I can't say, but that's the very reason why I have never used plastic in any operation that was critical. That, and the appearance of a bush-league operation. I don't mean to sound like I'm trying to be rude----but I had an image to uphold, so my customers had confidence in my work. They were free to inspect my facility--so I tried to present a professional image. I don't think working out of buckets projects that image very well. YMMV.

On another board where I spend my time, one of the contributors is a retired college dean. His sig line is "You are what you write". 

I firmly believe that to be the case, and also believe that the work you do represents you. I have a hard enough time passing myself off as a human being without going out of my way to prove I'm not. I highly recommend proper labware when dealing with values----as well as tried and proven methods, assuming your goal is extracting and refining precious metals for gain (I see a difference if your objective is research)----but then that's me------and I don't profess to speak for anyone but myself. 

Harold


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## NobleMetalsRecovery (Jan 4, 2009)

Thank you. Well said and well taken.


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## EVO-AU (Jan 5, 2009)

Randy: I found the priced book you were referring to, seems a lot cheaper than 116 + . Go for it. I tried some rare book sellers too, but not much difference. Phill


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## EVO-AU (Jan 5, 2009)

Goldsilverpro: In one of my books there is a test for gold using the mirror principle. I know just where it is; I'll post tomorrow. Really interesting. I too have a few books, but not the huge libraries you gentlemen have. I collect also, but the different things I find on the forum is a lot cheaper than buying books anymore. Evo


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## EVO-AU (Jan 6, 2009)

Silvergoldpro: Here is the test.

From an A/R solution, or any leached solution for that matter ( probably ): With a straight-tip glass eye dropper -

Suck up a drop or two of the solution and quickly hold the dropper horizontal, keeping the drop not more than 1/8 inch from the end of the tip. Hold it there and cause it to evaporate under a heat lamp or over a low flame without spattering. Then remove the rubber bulb. Heat the TIP over a Bunsen or Tirrel burner until it softenss, rotating it until a little round ball or sphere forms ( about 3/16" ). This will serve as a magnifier and if only 1 ppm of gold is present a film of mettalic gold will show.

Some authorities claim a pink line, or reddish thread, willl show against a dark background if as little as .95 ppm of gold is present.

I love history and researach. Ain't it fun ? Phill


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## EVO-AU (Jan 7, 2009)

Gentlemen and ladies: Whatever. The las line in my previous post reads .95 ppm - should be .05 ppm. Big difference. Sorry about that.. The fingers move faster than the brain sometimes. Phill


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## jimdoc (Jan 7, 2009)

Evo,
It is always better to edit your original post, than to correct it in
another post. It helps keep the misinformation factor down, and
the correction post may not always be noticed. There should be
an edit box in the right corner of all your posts.
Jim


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## EVO-AU (Jan 8, 2009)

Jimdoc: Thank you for the info, as you notice I am not a computer person. But I am learning. Phill


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## 61 silverman (Feb 18, 2009)

Hi, everyone this is a very interesting post,, One thing that I noticed that was not mentioned is that if you do perhaps use dirty "glassware" even if it is only a fingerprint , The oil on your skin will cause a high surface tension in the solution.. From HOKE'S book "A SINGLE DROP OF LIQUID DISH SOAP CAN BE ADDED.." This will relieve the surface tension and most too all film type of material will settle.. Mark


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