Hydrogen Sulfide danger
10 messages in this thread
H2S (AKA Hydrogen Sulfide) is deadly in concentrations as low as 700 ppm.
Olfactory paralysis and loss of detection commences around 100 pmm. Just
'cause you don't smell it doesn't mean it's not thee. I work in a plant that
handles in excess of 60 tons/day of H2S. That makes for a lot of ppm's in
anyone's book. Lead acetate tape is a useful indicator of H2S at low levels.
It could save your nose. I don't know of a simple, safe qualitative test for
arsenic.
I just have to upload the MSDS on chemicals typically encountered by
rockhound/geologist types. This is a good reminder for me, thanks!
Michael
Hi, Michael–
"I don't know of a simple, safe qualitative test for arsenic." – does that
mean the heat-and-sniff-for-"garlic"-test is unreliable or unreasonably
dangerous or both? I have tended to assume the "garlic" test is dangerous but
not quite as bad as H2S; maybe my assumption that As would be emitted in lesser
quantities from arsenides than H2S from sulfides? What is the garlic smell,
AsO3 or some such?
–Doug
Doug,
The "garlic" smell is arsine gas, AsH3. You can also get stibine SbH3 from
antimony containing minerals, and phosphine PH3 from a -few- phosphorous
containing minerals laid down in hydrothermal reduction zones. They all smell
garlicy.
In a lab, if you sniff one after another, you can learn to tell them apart.
These days, what with the Safety Nazis, such an experimental procedure would be
Ganz Verboten, because all three are really nasty poisons. Personally, I think
it would be darn near impossible to volatilize enough from a hunk of rock at
room temperature to cause trouble. All of these gasses are detectable at very
low concentrations and they all smell BAD.
The biggest failure of the "sniff" test is that it fails if the arsenic species
is fully oxidized, or complexed with sulfur. A more sensitive test might be to
volatilize the arsenic in the reducing zone of a blowpipe and note the garlic
odor of the resulting gases.
There are a whole lot of wet tests for arsenic, but offhand I can't think of
any that would be suitable for someone in the field.
— Norm
Hi, Norm–
Thanks for the info. That stibine smells garlicky also means that the odor
did not really help Chris' attempt to distinguish pearceite
[(Ag,Cu)16(Sb,As)2S11] from polybasite [(Ag,Cu)16(As,Sb)2S11], which started
this discussion. Chris, I hope you are reading this!
Getting phosphine from a mineral surprises me. I expect phosphorus to always
occur as phosphates, and getting phosphine from them seems tough without
extreme reducing conditions. Are there occasional phosphides among the
minerals or something? Phosphonium ions (I am assuming there is a phosphorus
analog to the ammonium ion)??
–Doug
Doug,
You can find both phosphides and phosphonium salts among minerals from a few
hydrothermal reducing zones. Most often, though, you find hypophosphites, that
can decompose when acidified into phosphine and phosphate. Not to worry,
though, these are really uncommon. When they occur at all, they occur along
with native metals (arsenic, antimony, copper) and their sulfides, selenides,
etc. The reduced phosphorous compounds are not stable with respect to air, so
once exposed, their lifetimes are quite short.
A good place to look for these fleeting things is in volcanic fumaroles, below
the level at which native sulfur deposits. Though I'm not sure I would
describe some place with superheated steam and hydrogen sulfide as a "good"
place, on any terms. In fact, it's more reminiscent of that Christian place
for bad people…
— Norm
Hi, Norm–
That is interesting about hypophosphites. Is that a PO2 ion? If these are as
unstable in air as they sound, but can survive inside an ordinary specimen,
perhaps one can simply break open an ore specimen and smell "garlic". In a
sulfide ore, might that even be a quick-and-dirty diagnostic test for
phosphorus?
–Doug
Doug,
The hypophosphite ion is H2PO2-, with the other two hydrogens being bound
directly to the phosphorous. I would presume it would be stable inside of
solid crystals, but it air-oxidizes very rapidly. If I cracked open a rock and
found a garlic smell, I would suspect arsenic or phosphorous all right.
These ions form as minerals when superheated water under pressure is reduced by
contact with low-oxidization species (usually iron) forming dissolved hydrogen.
Typically, the iron is present as iron carbides, and is present in blueschist
facies in subduction zones. The water (steam – remember, it's a superfluid
under pressure, and comes from the water of hydration of subducted minerals.
The hydrogen can generate reduced metals and metaloids, and even reduced
phosphate species. Farther up towards the surface, the hydrogen can reduce
sulfate minerals to hydrogen sulfide. The hydrogen sulfide breaks down at the
surface of the vents, and deposits elemental sulfur.
A good place to obtain samples of hyperreduced minerals is from carbonatites
brought up in oil well cores, or from the bottom metamorphic facies of
anthracite coal seams. If you smell a sulfur-containing well core, you can
distinctly smell hydrogen sulfide. Sulfur itself does not give off this odor,
so you can be certain that there are reduced species in the limestone, which
can include calcium and magnesium hydrosulfides. Cores from the Gulf of Mexico
sometimes include phosphoapatite seams, and it is within these seams that you
can find the hypophosphite minerals, usually as contact metamorphism between
the phosphates and the carbonatite matrix. It's very visible in thin section.
Even though the processing (wet grinding) destroys the hypophosphites, the
crystal structure remains.
— Norm
Hi, Norm–
It is interesting to learn of minerals so volatile in our familiar environment
that rockhounds can hardly meet up with the minerals, just the remnants of
their reactions with air. I had thought of the water-soluble and
sunlight-sensitive types as being the least durable.
Hmm.. is phosphine or some relative the cause of the odor of _real_ garlic?
–Doug
Hi, Doug-
Chris, I hope you are reading this! >
I'm following this discussion with great interest; however, the chemistry is
way over my head, so I'm not contributing. Kitchen sink geology/chemistry for
the moment is stritly verboten, but I shall be in touch again when I get the
results on the specimens I sent to the Romero Museum for analysis. I got hold
of yet more silver sulfides – sulfosalts – arsenates this weekend, including
habits that are new to me. They are from the same, greatly altered shoot, but
from about 1,350 feet down. This is lower than all previous mining work in the
shoot and there are no similar specimens in the local School of Mines
collection for comparison. One interesting aspect of the crystals is that they
are nearly all highly etched and, in fact seem to be spongey-looking
pseudomorphs of hexagonal plates – ?Polybasite. In most cases, the hexagonal
plate shape has almost deteriorated to the shape of fish scales. However, there
are occasional acanthite crystals among these pseudos on the matrix, which is
massive silver sulfide or whatever under a thin layer of chalcopyrite. The zone
is extremely acid, to the extent that tram rails and air pipes are corroded
very quickly.
If anyone cares to send me technical questions on this deposit, I shall do my
best to get technical answers from the mine geologists or the government mining
advisory council, which has an office in the area.
I shall certainly take samples to Tucson in February 95, if anyone cares to
take a look or a sniff.
Chris
Hi, Chris–
Sulfides and acid — it is a wonder the miners are not driven out by the smell
of hydrogen sulfide! Some sulfide minerals, like sphalerite, produce some
modest fizzing with the hydrochloric acid test, like carbonates but smelly,
because it is hydrogen sulfide rather than carbon dioxide being generated by
the reaction.
–Doug