From: Breukel, C. (HKG) (C.Breukel@lumc.nl)
Date: 02/11/03-02:40:20 AM Z
Dick,
As you probably know I have successfully made Gold chloride by dissolving
solid gold in aqua regia, and reported about it both on the list and in PF.
I used professional lab equipment and proper safety measures. It goes
without saying it is dangerous stuff and you must be careful. I do not want
to dispute below accident, but I do have some remarks. Both cases describe
tightly closed waste bottles: well at our lab that is a big NONO, never
tightly close a waste bottle, and our caps have a vent on it.
Second point: it is not stated if both waste bottles were empty, so I assume
that other (organic) waste could have been there, thus causing these
explosions.
On the protocol described by Liam: one works with an open container in a
fume hood or in a well ventilated space (outside), and the aqua regia is
gradually loosing is strength during the slow dissolving (at room
temperature, do not heat it of course!) the gold. I had to add extra fresh
aqua regia to get the gold soluted. Finally you neutralize the acid by
slowly adding calcium carbonate to it. In short I am still convinced if you
use your head (as these students below did NOT do), so you know what you do,
the dangers are exaggerated IMHO. But this not for everybody for sure! (Btw
how many people have excess to nitric and hydrochloric acid, pure anyway)
Best,
Cor
> -----Original Message-----
> From: Richard Sullivan [mailto:richsul@earthlink.net]
> Sent: Monday, February 10, 2003 7:42 PM
> To: alt-photo-process-l@sask.usask.ca
> Subject: Kitchen brewed gold chloride! Not!
>
>
>
> Several years ago there was a brouhaha here over an article
> in Post Factory
> No 3 on making gold chloride in your kitchen or darkroom.
>
> The issue at hand was safety. I believe some correction were
> made in No 4
> but the problem still exists as many here might read No. 3
> without the
> benefit of the corrections in No 4. It is highly doubtful
> that anyone would
> try this trick at home but someone just might as the article
> proposes just
> such a project.
>
> Several had said here that aqua regia would not explode in closed
> containers. Wrong!
>
> Liam Lawless, author of the article, said the following June
> of 1999 on the
> list via another members repost or forward.
>
> Liam says:
>
> >We have perhaps been remiss in implying that this process
> can be carried
> > >out indoors, which it definitely should not without the
> proper equipment,
> > >etc., but the only other point that gives me real cause
> for concern is your
> > >assertion that stored aqua regia could explode.
>
> Not only my assertion but that of the American Industrial
> Hygene Association!
>
> >I have, therefore, spoken
> > >to a chemist about this today (whose name I shall not give
> as he has
> > >nothing to do with this debate, but who has some
> interesting views on
> > >safety and responsibility that I hope he will one day
> share), and the gist
> > >of what he told me is as follows.
> > >
> >Aqua regia is a stable mixture of acids that will not
> spontaneously explode
> > >at normal temperatures, though a small amount of pressure
> will build up in
> > >its container until any air present is saturated with the
> acid vapours. It
> > >should, of course be kept in a glass or plastic container
> with screw cap,
> > >which is capable of withstanding the small build-up of
> pressure that
> > >occurs. And the general rule for acids is that they should
> be stored in a
> > >cool, dark place; heat increases the pressure, and light may cause
> > >photolysis that in turn causes decomposition and the
> liberation of gases.
> > >It is also important that the container is clean, to avoid
> contaminants
> > >that could catalyse decomposition.
>
> This is patently wrong and compounds the error in PF No 3.
>
> To add to the warnings I have found the following at:
>
> http://www2.umdnj.edu/eohssweb/aiha/accidents/explosion.htm#Two
>
> Do a page search on "aqua regia" as the pertinent part is
> about 80% down
> the page. It is from the American Industrial Hygene
> Association on the New
> Jersey Medical and Dental College site. It highlights two
> cases of aqua
> regia explosions. These were not just caps blowing off but violent
> explosions shattering the glass bottles with enough force to
> break other
> nearby bottles. Had someone been in the room and been the
> subject of flying
> glass and hot aqua regia spray it could have been very messy.
>
> The text follows:
>
> >Two Explosions Involving Aqua Regia (top)
> >Key Learning Points
> >1. Use a reagent that is milder than aqua regia for cleaning
> glassware if
> >it will suffice.
>
>
>
> >2. Do not take aqua regia out of the fume hood in which it
> was prepared,
> >and do not store it there either; make only what you need
> and destroy the
> >residue. Aqua regia can be destroyed by cautious and careful
> dilution with
> >water - talk to your supervisor or your safety office for a detailed
> >procedure. If necessary, the solution can then be
> neutralized and disposed
> >of in the approved manner.
>
>
>
> >3. Never put aqua regia in a closed container or near flammables.
>
>
>
> >There have been explosions involving aqua regia ( a mixture of
> >hydrochloric acid and nitric acid) reported at two
> universities. Both of
> >the incidents took place in chemistry laboratories.
>
>
>
> >In the first incident, a graduate student was using aqua
> regia for the
> >cleaning of NMR tubes. When he was finished, he placed the
> residues (about
> >50-60 ml) in a 4 litre waste bottle, capped it tightly and
> placed it in a
> >flammable storage cabinet. Approximately one hour after the
> bottle was
> >placed in the cabinet, it burst, breaking an adjacent bottle
> of pyridine.
> >Luckily, the pyridine did not ignite and other nearby
> bottles containing
> >flammable solvents did not become involved. The pyridine
> leaked onto the
> >floor, where it dissolved floor tiles and created a
> lingering bad smell.
> >The second incident occurred in a fume hood in a synthetic chemistry
> >laboratory. A tightly closed waste bottle containing used aqua regia
> >exploded, most probably due to pressure buildup inside the bottle.
> >Since the sash was not completely closed the broken waste
> bottle was not
> >contained. Broken glass as well as some liquid acid waste
> were thrown out
> >of the hood. Since nobody was near the hood at that moment,
> there were no
> >injuries. Moreover, a nearby bottle of mercury nitrate waste
> was also
> >broken as well as the secondary container, so that a small
> spill (less
> >than 1 liter) of liquid acid and solid mercury nitrate
> occurred inside the
> >hood.
>
>
>
> >What is aqua regia?
> >Aqua regia has been used by chemists for centuries,
> especially as a medium
> >for dissolving noble metals but also for other purposes. It
> is a mixture
> >of concentrated hydrochloric and nitric acid which forms a powerful
> >oxidizing medium. Mixing an oxidizer with organic materials
> may result in
> >a highly exothermic reaction. Even without other materials
> present, a
> >chemical reaction occurs slowly and brown fumes of NO2 can
> be observed (in
> >freshman chemistry terms, nitric acid is reduced and
> hydrochloric acid is
> >oxidized). The activity as a dissolving agent decreases
> slowly and so, by
> >definition, the solution is unstable - it should be used
> "freshly prepared".
>
>
>
> >Rules for using aqua regia
> >Aqua regia is often used as a substitute for chromic sulfuric acid
> >cleaning solutions. However, aqua regia is also corrosive
> and strongly
> >oxidizing. It is essential for some purposes but should not
> be used for
> >routine cleaning of glassware. If a milder reagent will
> suffice avoid
> >using aqua regia. Alternatives include ultrasonic baths, alconox or
> >similar detergents, Pierce RBS-35 (available from VWR) or similar
> >detergents or biodegradable surfactants.
>
>
>
> >Be aware that sufficient pressure can build up in a short
> amount of time
> >to burst the container, even from a very small volume of aqua regia.
>
>
>
> >If it is decided that aqua regia is needed, wear protective clothing
> >(goggles, gloves, coat) and work in a clean well-ventilated
> fume hood.
> >Keep the sash down when reactions are in progress.
>
>
>
> >Never take aqua regia out of the hood.
>
>
>
> >Prepare it, use it, and destroy any excess in the hood in
> which it was
> >prepared.
>
>
>
> >
> >Only prepare the amount of aqua regia you need for immediate
> use. Never
> >store it and never put it in a closed vessel, since evolved
> gases will
> >cause a pressure build-up and possible explosion.
>
>
>
> >Aqua regia is a strong oxidizer. It is incompatible with
> organic solvents,
> >flammables and any reducing agents.
>
> --Dick Sullivan
>
>
>
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