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Thread: Making aqua regia

  1. #21
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    Re: Making aqua regia

    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.
    The Giants of this world that hold gold know what it's worth... when it finally gets there they will still not liquidate their "stocks"... because gold as a store of purchasing power has an infinite time horizon. These Giants aren't interested in "catching the top" like Western traders. - para/FOFOA

  2. #22
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  3. #23
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    Re: Making aqua regia

    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.
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  4. #24
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    Re: Making aqua regia

    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.
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  5. #25
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    Re: Making aqua regia

    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.
    Be kind, for everyone you meet is fighting a hard battle.

  6. #26
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    Re: Making aqua regia

    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!
    Be kind, for everyone you meet is fighting a hard battle.

  7. #27
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    Re: Making aqua regia

    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]
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  8. #28
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    Re: Making aqua regia

    Quote Originally Posted by uranian
    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.
    The Giants of this world that hold gold know what it's worth... when it finally gets there they will still not liquidate their "stocks"... because gold as a store of purchasing power has an infinite time horizon. These Giants aren't interested in "catching the top" like Western traders. - para/FOFOA

  9. #29
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    Re: Making aqua regia

    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
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  10. #30
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    Re: Making aqua regia

    Quote Originally Posted by uranian

    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.

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