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uranian
8th June 2010, 09:51 AM
Anyone have experience of doing this?


Aqua regia or aqua regis (Latin for royal water or king's water) is a highly corrosive, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and concentrated hydrochloric acid, usually in a volumetric ratio of 1:3 respectively. It was named so because it can dissolve the so-called "royal metals," or noble metals, gold and platinum.

I can get hold of the acids, but I've been reading that the 1:3 ratio isn't as straightforward as it seems, as we're talking moles rather than volume (contrary to what the wiki entry quoted above says). Given that my chemistry knowledge is distinctly lacking, I'm hoping someone can offer useful advice as to the production of aqua regia.

(to the curious, basically I'm thinking of doing this because I can buy 20ml of pre-mixed aqua regia for about £25, and I can buy 2.5 liters of hydrochloric acid and 2.5 liters of nitric acid for about £50, and paying 250 times the cost of the constituent parts just peeves me :boom)

Saul Mine
8th June 2010, 10:25 AM
You don't say what country you are in. In the USA you can get hydrochloric acid at any hardware store for $7 a gallon, roughly $1.75 per liter. Nitric acid comes from the gardening supply store labeled as stump remover (potassium nitrate).

mamboni
8th June 2010, 01:47 PM
Anyone have experience of doing this?


Aqua regia or aqua regis (Latin for royal water or king's water) is a highly corrosive, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and concentrated hydrochloric acid, usually in a volumetric ratio of 1:3 respectively. It was named so because it can dissolve the so-called "royal metals," or noble metals, gold and platinum.

I can get hold of the acids, but I've been reading that the 1:3 ratio isn't as straightforward as it seems, as we're talking moles rather than volume (contrary to what the wiki entry quoted above says). Given that my chemistry knowledge is distinctly lacking, I'm hoping someone can offer useful advice as to the production of aqua regia.

(to the curious, basically I'm thinking of doing this because I can buy 20ml of pre-mixed aqua regia for about £25, and I can buy 2.5 liters of hydrochloric acid and 2.5 liters of nitric acid for about £50, and paying 250 times the cost of the constituent parts just peeves me :boom)


Please be extremely careful with this stuff, or you will experience that scene in Alien when the crew tried to cut through the parasite attached to William Hurt's face.

JohnQPublic
8th June 2010, 02:12 PM
You don't say what country you are in. In the USA you can get hydrochloric acid at any hardware store for $7 a gallon, roughly $1.75 per liter. Nitric acid comes from the gardening supply store labeled as stump remover (potassium nitrate).


Isn't the hydrochloric acid actually muriatic acid? This is not 100% HCL. It is pretty dliute. You should use laboratory or at least industrial grade chemicals. You should also have proper facilities, protective equipment, and some training before playing with concentrated acids.

mamboni
8th June 2010, 02:20 PM
You don't say what country you are in. In the USA you can get hydrochloric acid at any hardware store for $7 a gallon, roughly $1.75 per liter. Nitric acid comes from the gardening supply store labeled as stump remover (potassium nitrate).


Isn't the hydrochloric acid actually muriatic acid? This is not 100% HCL. It is pretty dliute. You should use laboratory or at least industrial grade chemicals. You should also have proper facilities, protective equipment, and some training before playing with concentrated acids.


Yes, one must use fuming HCl and Nitric.

madfranks
8th June 2010, 06:52 PM
I love aqua regia - to me there's just something fascinating about being able to dissolve gold into this "royal water". I always thought the perfect crime would be to get a job at the mint where you have access to all the gold, somehow line a thermos with something so it could hold some of the aqua regia, bring your thermos to work in your lunch box, sneak some gold blanks in the thermos and leave with no one the wiser. Ha ha, of course I would never do this, nor have I ever held a job at the mint, although it might be fun... ::)

http://www.youtube.com/watch?v=iwnKU89CCdI

uranian
8th June 2010, 11:57 PM
I'm in the UK. 70% pure nitric acid (http://www.reagent.co.uk/nitric-acid-ar/nitric-acid-ar-1-42-sg.html) is available for £25 (2.5 liters), approx. 40% pure (beyond this apparently it just evaporates too quickly to be of practical use) hydrochloric acid (http://www.reagent.co.uk/hydrochloric-acid/hydrochloric-acid-ar-1-18-sg.html) for £18 (2.5 liters).

Mamboni, thanks for your concern. I've been talking to the guy at reagent (the shop in the UK) and he's been trying to put me off buying the acids to mix myself too (he was slightly relieved to hear that I have a decent air filter I think!). I shall attempt to not replicate Hurt's face. I do understand that these are dangerous chemicals, as I've been using premixed aqua regia for a while now. I know that the mixture will fume as it's being mixed. I also know that a fair few jewellers will give their AR a whiff before use to see if it's fresh (on the basis that if they start coughing, it's fresh), though I tend not to do that myself!

No thoughts on the ratio of the acids? I did come across this thread (http://www.goldrefiningforum.com/phpBB3/viewtopic.php?f=39&t=311) in the gold refining forum, which suggests the following mix for testing 18 carat gold:


5.9 mL nitric - 5.9mL distilled water - 17.8 mL hydrochloric

so I'm thinking that it is just a simple 3:1 volume mix of the 2 acids. Certainly with 2.5 liters of each acid I'll have enough to last me a lifetime, that's the smallest size that reagent sell.

uranian
9th June 2010, 02:54 AM
an interesting question, but my use for aqua regia is to test gold, rather than dissolve bucket fulls of the stuff!

Saul Mine
9th June 2010, 03:49 AM
You don't say what country you are in. In the USA you can get hydrochloric acid at any hardware store for $7 a gallon, roughly $1.75 per liter. Nitric acid comes from the gardening supply store labeled as stump remover (potassium nitrate).


Isn't the hydrochloric acid actually muriatic acid? This is not 100% HCL. It is pretty dliute. You should use laboratory or at least industrial grade chemicals. You should also have proper facilities, protective equipment, and some training before playing with concentrated acids.


Yes, one must use fuming HCl and Nitric.


Baloney. Aqua regia forms naturally from nitrates in the soil and acids in rain. The product is good enough to dissolve gold in streams (even while the water is still safe to drink) and has long been a pesky nuisance to gold miners.

gunDriller
10th June 2010, 03:32 PM
I love aqua regia - to me there's just something fascinating about being able to dissolve gold into this "royal water". I always thought the perfect crime would be to get a job at the mint where you have access to all the gold, somehow line a thermos with something so it could hold some of the aqua regia, bring your thermos to work in your lunch box, sneak some gold blanks in the thermos and leave with no one the wiser. Ha ha, of course I would never do this, nor have I ever held a job at the mint, although it might be fun... ::)

mining gold is mining gold, it's legal.

but if you're gonna have that solution in a thermos you'd better have a bunch of safety stuff, safety glasses etc.

uranian
11th June 2010, 01:23 PM
acids were delivery today, i'll let y'all know if i burn my face off!

Ragnarok
12th June 2010, 07:27 AM
One suggestion - don't mix up more than you are going to use for one or a few tests/ experiments. This way you will have three very useful acids around. ;)

2c, R.

uranian
12th June 2010, 01:34 PM
thanks ragnarok, i've read that the shelf life of aqua regia is only 4 weeks, so i'm not planning on making more than 10ml at a time. that said, i've got some here that's a few months old and still works (reaction times are a little slower, that's all).

i dunno if i'm going to horrify the chemists with this question at my lack of knowledge (to be fair, i dropped chemistry at 14), but i'm thinking it wouldn't be a bad idea to have something to neutralise the acids handy in the unlikely event that i ever do have a spill. given that HCL has a very low ph (i.e. is extremely acidic), would lye (sodium hydroxide) be a useful substance, given that it's extremely alkaline, to neutralise the acid with? or am i likely to end up with even more of a problem if i dunked some lye on some spilt hydrochloric acid?

Saul Mine
12th June 2010, 07:19 PM
Use baking soda. Not lye. Baking soda.

uranian
13th June 2010, 04:06 AM
thanks, saul. why?

Saul Mine
13th June 2010, 07:25 AM
Because baking soda is cheaper, easier to find, and doesn't dissolve skin.

uranian
13th June 2010, 12:52 PM
3 good reasons!

crazychicken
13th June 2010, 02:52 PM
There is a lot of information being posted here on the subject of making Aqua Regia.

Some Excellent, some not.

Since the use of any chemicals can be dangerous it is suggested you get your information from PROFFESSIONAL SOURCES, since the cost of being wrong can be quite high.

Does anyone here believe everything on the internet is TRUTHFUL?

Then with the answer you gave consider the danger of acting on nonprofessional information.

This is no shot at anyone. This is just a suggestion to be extremely careful.

I have no dog in this fight. Just concern.

CC

Gaillo
13th June 2010, 03:01 PM
+1 to CC's post.
Some types of chemistry are SERIOUSLY DANGEROUS, folks... I know this from personal experience.

From Wikipedia:


Aqua regia is itself very corrosive and has been implicated in several explosions due to mishandling.[2]

Due to the reaction between its components resulting in its decomposition, aqua regia quickly loses its effectiveness. As such, its components should only be mixed immediately before use.


Decomposition of aqua regia

Upon mixing of concentrated hydrochloric acid and concentrated nitric acid, chemical reactions occur. These reactions result in the volatile products nitrosyl chloride and chlorine as evidenced by the fuming nature and characteristic yellow color of aqua regia. As the volatile products escape from solution, the aqua regia loses its potency.

HNO3 (aq) + 3 HCl (aq) → NOCl (g) + Cl2 (g) + 2 H2O (l)

Nitrosyl chloride can further decompose into nitric oxide and chlorine. This dissociation is equilibrium-limited. Therefore, in addition to nitrosyl chloride and chlorine, the fumes over aqua regia contain nitric oxide.

2 NOCl (g) → 2 NO (g) + Cl2 (g)

In short, DO NOT STORE in a sealed vessel, and mix just enough for your immediate needs, and dispose the remainder afterwards.

uranian
13th June 2010, 03:54 PM
In short, DO NOT STORE in a sealed vessel, and mix just enough for your immediate needs, and dispose the remainder afterwards.

i'd been wondering about that, thanks for the confirmation, gaillo. odd thing is that the AR i bought previously from a professional jewellery services company appears to be in a sealed bottle. that info about it losing its effectiveness is simply wrong in my experience, as i'm using 6 month old AR and it's still doing the job.

CC, no dogs from here either, i think this (and the gold refining forum) are both useful places to get info on this. i was hoping you might chime in with a nugget of info, as i've read your thread about the mobile solvent extraction unit. i'm planning on making my first few mls of AR in a few days, if i stop posting, you know why!

Ragnarok
15th June 2010, 08:39 AM
It may depend on how concentrated your acids are. The more dilute the less (potential) problem, but I don't know enough about aqua regia in that regard. I understand it is made from strong concentrations of the components and dilution may render it much less effective.

2c, R.

Saul Mine
15th June 2010, 11:12 AM
Basement Chemistry For The Prospector (http://webpages.charter.net/kwilliams00/bcftp/bcftp.htm)

uranian
15th June 2010, 01:24 PM
more thanks from me, ragnarok and saul. from your link, saul:


It can be explosive and ruin your whole week by drenching you in hot concentrated sulfuric acid.

caused me a chuckle. useful info that i've gleaned so far is to add "Do like you outta, put the acid in the water"

as to the strengths of the acids, i've bought the strongest possible. i'm almost out of 18ct test solution so will be making some soon. i don't see mention in the wiki entry of adding water to AR, but i do in the gold refining forum; think what i'm going to do is try without, compare the reaction to some pre-existing AR, and see how i go from there.

uranian
15th June 2010, 01:37 PM
Aqua regia is a very special case. This is a mixture of concentrated acids, which is not only a very strong acid, but is also a very strong oxidizing agent. It is capable of oxidizing gold to gold chloride, which is soluble in water. Yeah, I heard of it but where do I get it? You don’t get it, you make it. Aqua regia is nothing more than a mixture containing 3 parts of concentrated hydrochloric acid to 1 part of concentrated nitric acid. Actually this universally used formula is not quite correct. If you want to make it right you mix 9 parts of nitric to 41 parts of hydrochloric but the 3/1 formula is good enough for government work. This is a rather fearsome reagent. If you are going to make/use it always wear plastic gloves. Someday you will thank me for this advice.

Aqua regia dissolves gold and all the platinum metals very rapidly (especially if hot). It will also dissolve damn near anything else in your sample. Silver, iron, magnesium, manganese, aluminum, etc. In fact it will attack any metal. The stuff emits a red vapor that is very irritating. It’s nasty stuff and unless you really have to use it, it is better to do the job some other way.

If you dissolve gold in aqua regia and want to recover it you will find that you must remove the nitric acid by evaporating the solution with heat. This will produce lots of the red vapor. You must not let the solution go completely dry. Stop heating when you still have just a little liquid left. Now you must add more hydrochloric and repeat the procedure. Repeat this evaporation 3 times or until there are no more red fumes coming off. Now add hydrochloric so that you have enough liquid to work with. All the metals will be in solution as their chloride salts. If you dilute this solution with an equal volume of water you will probably get a white cloud of silver chloride which you can filter off. Now to recover you’re gold. Probably the easiest is to cement it down by adding pieces of zinc or aluminum. You will get a black-brown precipitate in the bottom that you can smelt back to nice yellow gold. There are numerous other ways to recover the gold but that’s another page.

uranian
15th June 2010, 04:47 PM
a little basic info if ever anyone discovers this thread and finds it useful:


To answer "Is It Gold?"

With a small file, make a scratch in an inconspicuous spot. While wearing rubber gloves, use a wooden, glass or plastic stick to apply a drop of nitric acid to the filed spot. Observe the reaction. When done, rinse everything well in running water.

If there is no reaction, it's gold. If there's a bright green reaction, it's base metal. If there's green in the scratch, it's a gold layer over base metal (goldplate). If there's a milky reaction in the scratch, it's a gold layer over silver.

To answer "What Karat Is It?"

Determining karat requires a testing kit containing nitric acid, aqua regia, samples of known karat, and a touchstone of slate or ceramic.

The gold object to be tested is rubbed on the stone ("touched") to leave a streak. A parallel line is made with one of the test pieces of known karat. Both marks are flooded with acid and the reaction are observed. When the sample colors at the same rate as the test streak, a match has been made. Nitric acid is used for low karat golds; aqua regia is needed for higher karats.

personally i've found putting acid on the item is easier than using a touchstone, but that seems to be a matter of preference. probably does less damage to use a touchstone, at least.

uranian
16th June 2010, 09:50 AM
more useful advice from the company that sold me the acids:


The bottles will be air tight, but the smaller bottles we use for our Gold Test Kits and have so far had no reported issues of them gassing off

Provided they’re kept out of extremely high temperatures, there shouldn’t be an issue

The best way to make the aqua regia is outside - mix the components with the lid on in with a decent swirling motion then carefully take the lid off the mixing container and leave it in a safe place for half an hour to cool down. After this initial period it shouldn’t gas off to any significant amount to cause you a problem.

advice from the rather grumpy types at the refining forum suggests that adding water to the mix makes the nitric acid more effective; one user there reports that straight nitric will dissolve silver, but noticeably more quickly if water is added. i'll report my own experience of this when i have some!

crazychicken
16th June 2010, 10:36 AM
Dilute HNO3, I use 18%, @ 180f will digest silver quite rapidly.

Filter the liquid--The liquid is silver nitrate

Put the liquid in a graduated cylinder, drop NaCl crystals--non-iodized salt--into the liquid. As the salt decends the little "tails" that form are silver chloride. When no more "tails" are formed filter the liquid. The sludge in the filter is silver nitrate. Rinse with hot water primarily to dissolve any NaCl crystals.

Dry it.

To verify it is silver chloride put some in the sun.

Silver Chloride will turn purple.

Good luck, have fun with it.

CC


[/quote]
advice from the rather grumpy types at the refining forum suggests that adding water to the mix makes the nitric acid more effective; one user there reports that straight nitric will dissolve silver, but noticeably more quickly if water is added. i'll report my own experience of this when i have some!
[/quote]

Ragnarok
18th June 2010, 12:25 PM
The stuff emits a red vapor that is very irritating...
This will produce lots of the red vapor....
Repeat this evaporation 3 times or until there are no more red fumes coming off....


FYI, that red vapor/fumes is nitrogen dioxide (NO2). Do not breathe it - any of it - at all. If/when inhaled, it turns into nitric acid on contact with moisture in the lung tissues. The damage may be delayed and you can get a fatal amount without knowing it until later. You might look up nitrogen dioxide online for more info.

If you're doing this indoors you must do it under a proper ventilated hood imo.

R.

uranian
18th June 2010, 02:22 PM
thanks for that, ragnarok. i've never seen red fumes coming off the aqua regia i've bought from jewellery supply shops, although it certainly smells bad, like chlorine. i read that many jewellers take a whiff to see if the stuff if still fresh, if that smell is NO2, that sounds like a very bad idea!


Nitrogen dioxide is toxic by inhalation, but this can be avoided as the material is acrid and easily detectable by smell. One potential source of exposure is fuming nitric acid, which spontaneously produces NO2 above 0 °C. Symptoms of poisoning (lung edema) tend to appear several hours after one has inhaled a low but potentially fatal dose. Also, low concentrations (4 ppm) will anesthetize the nose, thus creating a potential for overexposure.

http://n3chem.freehostia.com/NO2.jpg

CrufflerJJ
19th June 2010, 11:51 AM
advice from the rather grumpy types at the refining forum suggests that adding water to the mix makes the nitric acid more effective; one user there reports that straight nitric will dissolve silver, but noticeably more quickly if water is added. i'll report my own experience of this when i have some!


Please don't try adding water to concentrated acids. It's better to add the acids to water, rather than vice-versa. Unless, of course, you like having boiling acid spattered about.

When making your acid mixture, you might also try putting your beaker (or whatever inert mixing vessel you use) in an ice water bath. Also gently STIR the reagents as you mix them - don't just dump one into the other. That way, the heat of mixing the reagents is absorbed without any undue excitement.

Wear long sleeves, long pants (not shorts), decent shoes, nitrile rubber gloves, and goggles when mixing the acids.

If you store your mixture in a plastic bottle (polyethylene, for example), the oxidizing acids can make the plastic brittle, resulting in unplanned excitement when you handle the bottle.

uranian
19th June 2010, 12:07 PM
thanks to you too, cruffler. any idea if the chlorine-smelling fumes that come off the premixed aqua regia are nitrogen dioxide too? i tend to hold my breath when dealing with the stuff i've got, will be doubly careful if it transpires that the smell is NO2.

CrufflerJJ
19th June 2010, 06:40 PM
thanks to you too, cruffler. any idea if the chlorine-smelling fumes that come off the premixed aqua regia are nitrogen dioxide too? i tend to hold my breath when dealing with the stuff i've got, will be doubly careful if it transpires that the smell is NO2.


Gaillo's earlier post showed the decomposition products of mixing HCl & HNO3. Gaseous chlorine is released, so I suspect that the "chlorine-smelling" fumes are chlorine.

I'd rather not snort either Cl2 or NO2, thank you very much! Remember that chlorine was used as a war gas back during WW1. Nasty stuff, resulting in pulmonary edema (lungs filling up with fluid & other nastiness).

uranian
20th June 2010, 01:12 AM
always struck me that smelling the aqua regia to see if it makes you cough as a check whether it's fresh wasn't that wise, but i'm a little relieved to hear that it's apparently only during the production that it releases NO2. agreed that breathing in chlorine isn't a splendid idea too, and i'll continue to hold my breath when dealing with it!

uranian
20th June 2010, 01:29 AM
so it seems that nitric acid decomposes into nitrogen dioxide, which can then combine with water to form more nitric acid, hence a very bad idea to breath its fumes in.

similarly hydrochloric acid decomposes into hydrogen chloride, which can then again combine with water to form back into hydrochloric acid.

when combined, aqua regia decomposes into nitrosyl chloride and chlorine; while certainly neither of these are especially sensible to breath in, they're at least not as dangerous as the decomposition products of the individual acids.

hence the conclusion appears to be; extremely careful while producing the aqua regia (recommendations of doing outside seems extremely well justified), as the decomposition products of the individual acids are so dangerous (as they'll turn back into the acids in one's lungs if breathed in), and careful of the fumes of the aqua regia.

uranian
6th July 2010, 12:01 PM
well, i mixed up my first batch of aqua regia a few hours ago, and i'm still here to tell the tale, pulmonary edema apparently avoided so far! i wasn't so sure of the ratio of 3:1 given the different strengths of the acids (70% pure nitric acid, 40% pure hydrochloric acid), but the stuff works as expected when testing various bits of gold, which is what matters. only unexpected occurrence along the way was that the reaction between the 2 acids took longer than i'd expected; the guy from reagent had suggested waiting half an hour for the newly mixed AR to cool off, i gave it a few hours before the mix stopped bubbling.

thanks to all the helpful posters in the thread, i'd never have known quite how potentially dangerous this was without the useful info on the fumes from the original acids. so now i have 2.49 liters of each acid left, will take me a long time to get through the remainder!

madfranks
6th July 2010, 12:10 PM
Now that you've dissolved some gold, how do you plan on recovering it?

uranian
6th July 2010, 05:31 PM
i'm not dissolving gold, i'm testing it. i need to verify jewellery, and having seen one of the electronic mizar testing machines read 9 carat for something i knew to be plated, decided to go down the aqua regia road instead. it can be difficult to test chains with tiny links, and if there's loads of stuff to test i do still use the mizar machine as a quick/dirty test, but the acid test is indeed the acid test :D

Argentium
17th July 2010, 12:13 PM
I've made it once, definitely make it outside or use a fume hood. The reaction was much more violent than I had thought. Using an ice bath ain't a bad idea.

Dave Thomas
22nd July 2010, 10:52 PM
The concentration of the acids is what's going to be dangerous. If you've got 70% HNO3 you've got to get rid of all that water, same with the HCl. Like Argentium said, do it outside.

I think you can evolve NO2 from Potassium Nitrate by boiling it in Sulfuric acid, this releases NO2 which then precipitates out as Nitric acid as it cools with water vapor. A slow and arduous process.

Nitric acid is the mother of all explosives, so I'd bet you'd be on some sort of "list" after a purchase or two.

An even more exciting way of creating Nitric acid involves passing Ozone through water vapor, you can do this with a neon sign transformer, a copper tube and a humidifier. Fun stuff!

Ragnarok
23rd July 2010, 05:14 PM
Heating copper nitrate also produces NO2, leaving behind black copper oxide (CuO). I used this method in an experiment to make nitric acid (by bubbling the NO2 through water), and later used that to dissolve some silver to make silver nitrate.

^+1 on the neon sign transformer! I have a Jacob's ladder over which I placed a long transparent acrylic tube to better control the rising arc. By placing a cover on top, the speed of the arc's rise is reduced to a lazy pace, making it easier to observe. A potentially useful side effect is that NO2 is produced by the action of the arc on the air, and accumulates in the upper part of the tube.
I've been considering using that to make nitric acid and other nitrates - for example, bubbling the gas through a solution of potassium hydroxide would yield potassium nitrate (saltpeter), etc. Ain't chemistry fun!

Stay safe out there!
R.

uranian
23rd July 2010, 05:45 PM
Regarding royal blue, it is obtained thanks to an anodic dissolution caused by electrolysis, which makes it a lot more reliable for testing old gold in particular.

any sense, to any one? a brief google on this supposed method of testing gold has revealed no useful info at all.

gunDriller
24th July 2010, 07:11 AM
can someone please post a pic of their gold-dissolving area ?

workbench, fumehood, storage, emergency spill safeguards, protective clothing.

just wondering how i might fit this in if i moved some plants off the patio.

in the past when i worked on "fun-but-dangerous" stuff like melting metal in a kiln, i used a flat plastic tub about 2' x 3' filled with sand in case i needed to drop something fast.

uranian
29th July 2011, 03:41 AM
thanks to all for the info on this thread, i'm on my 4th or 5th bottle of AR now. my fume hood is actually my chimney, lol, i'm at least not dead yet via drowning in my own blood. i've branched out into schwerter salts too, you can just add a little potassium dichromate to nitric acid to make a silver test solution; seems to work on anything over 50% purity silver.