投稿者 新科学者 日時 2000 年 8 月 25 日 10:31:35:
回答先: ロシアの科学者、択捉島でピラミッド建設（ロイター） 投稿者 FP親衛隊長様、御解説きぼーん！ 日時 2000 年 8 月 25 日 10:18:55:
表紙あやしすぎ！
Outrageous fortune
A working mine in the crater of an active volcano? Are they crazy? Nicola Jones finds out
Illustration: Chris Nurse
ON AN island paradise off the north coast of Japan, there's a volcano
with treasure seeping out of its pores. All this summer, Russian scientists
will be landing on Iturup Island with lengths of timber over their
shoulders and a glimmer in their eyes. They are on their way to build a
wooden pyramid over Kudriavy's steaming vents, hoping to tap some of
the volcano's wealth before it vanishes into thin air. They are on their
way to bag some rhenium.
At $1450 a kilogram, rhenium is not your average element. An
extremely hard-wearing silvery metal, it is used in satellites, aeroplanes,
high-tech thermometers and tactical missiles, and it's a handy catalyst
for producing high-octane fuels. Rhenium is also extremely rare--hence
its hefty price tag. And yet Kudriavy is full of it. That's why researchers
are now hunkering down in the volcano's crater, taking the first risky
steps to turn the volcano into an operational mine.
Kudriavy caught the world's attention back in 1992 when Mikhail
Korzhinsky from the Institute of Experimental Mineralogy in
Chernogolovka and his colleagues stumbled on some strange rocks in
the rubble of the volcano's crater. The soft, light-grey fragments, which
everyone assumed were ordinary molybdenum sulphide, turned out to
be rhenium sulphide--the first known mineral of rhenium unpolluted by
other metals. It was dubbed rheniite, and contained an amazing 77 per
cent rhenium by weight.
That means Kudriavy is enriching rhenium from its gases by about eight
orders of magnitude, carefully excluding all the other metals found in
higher abundances, and spitting out metallic chunks that have been
described as anything from "beautiful" to just plain "weird". Why it should
do this is still anyone's guess. Kudriavy is just one bump in a string of
volcanic islands known as the Kuril Archipelago, a geologically young and
still active paradise. The last time its summit crater erupted was back in
1883, though mild explosions have happened since then and it still spits
lava down its western side. At present its summit holds a 300-metre
crater spattered with about a dozen fumarole fields, where the pent-up
gases violently escape at temperatures up to 950 ｡C, which is
remarkably hot--even for a volcano. It seems that only a vent smack in
the middle of the crater, spewing gases at 530 ｡C, is producing rheniite.
With the discovery of this rheniite in the early 1990s, Kudriavy started to
look like a treasure trove. And Korzhinsky's colleague, Genrikh
Steinberg from Russia's Institute of Volcanology and Geodynamics in
Yuzhno-Sakhalinsk, was getting ideas. "He was talking about getting a
dump truck and just carting the stuff off," says Terry Adams, president
of British metal mining company Adams Metals of Guilford, which
provides for about 65 per cent of the West's rhenium needs. And, he
adds, that still might not be such a bad idea. There are probably just 10
tonnes of the ore stocked in the volcano, says Adams, but "for a small
dedicated operation that's quite viable".
But the Russian researchers thought they could do better. If rhenium
was plopping out of the volcano as a mineral at the rate of several
grams per day, just how much was being belched out as a gas? Since
Kudriavy is relatively quiet, they had reason to be sceptical. Looking at
sulphur dioxide emissions, a common way of evaluating volcanic gas
production, Kudriavy only puts out about 75 tonnes of SO2 a day,
compared with 10 000 tonnes for hyperactive volcanoes. But if the
rhenium concentration were high enough, it might still be worth tapping
the gas.
So Tobias Fischer, assistant professor of volcanology at the University of
New Mexico in Albuquerque, went to Iturup with some of the Russian
team in 1996 to measure the amount of rhenium in Kudriavy's gases.
They found up to 6 micrograms per litre of condensed gas--10 times as
much as the average volcano.
So Steinberg, along with Alexander Kremenetsky and Felix Shaderman
from the Institute of Mineralogy, Geochemistry and Crystal Chemistry of
Rare Earth Elements in Moscow, devised a p
lan to swipe the island's
valuable gas. Their invention (patent pending) involves fitting a cap over
one of the volcano's fumaroles. The gas spews into the cap and is
funnelled through a pipe--helped along by a small fan--to a chemical trap
filled with an absorbent natural rock called zeolite. This Swiss-cheese
conglomerate of aluminosilicate, doped with various positive ions, has
many uses. For example, zeolite is found in a lot of washing powders,
where it extracts ions from the water, making it softer and more
effective for cleaning. You can also find it in cat litter, where it absorbs
moisture. And now you can find it on top of a Russian volcano.
Tests show that natural zeolite can absorb the rhenium as a disulphide
with the same formula as the mysterious rheniite. All you have to do is
heat the zeolite, and volatile rhenium sulphide emerges, while more
polar molecules such as water remain behind. So, will the process yield
enough rhenium to make it worthwhile? Outsiders are curious, but not
terribly confident. "It sounds far-fetched to me," says Rob Bell, a senior
research fellow with the Royal Institution of Great Britain, London, who
works on computer modelling with different forms of zeolite. "But not
completely impossible."
This month, Kremenetsky's team is
setting up a test pyramid--with a base
of 9 square metres--over one of
Kudriavy's rhenium-enriched
fumaroles, to see if the plan will work.
The pyramid is made of wood--another
risky aspect of the scheme. Kirill
Schmulovich, a geochemist from the
Institute of Experimental Mineralogy in
Chernogolovka, who was with
Steinberg when they discovered
rheniite, says his own experience on
Kudriavy was not very wood-friendly.
"Once, we put a stake in the soil,
about one inch in diameter," he
remembers. "The next year, no
stake." Whether it burned up, was
consumed by acidic volcanic belches or was knocked over and buried by
rubble, he doesn't know. Whatever happened, it didn't last.
Alexander Solov'yow, a colleague of Steinberg, objects to this criticism.
He says the Japanese had log structures on Kudriavy for years, and
claims that Schmulovich simply lost his stick. Still, the future has bigger,
better, more solid things in store. Kremenetsky plans eventually to cap
Kudriavy's fumarole field--covering about 35 per cent of the crater--with
a huge concrete or ceramic dome. Estimates of just how much rhenium
they'll catch vary widely. Fischer reckons that only 270 kilograms of gas
are emitted a year. How much of that could be caught he has no idea.
But the Russian rhenium-hunters are placing their bets an order of
magnitude higher, estimating that they'll get 2 tonnes in their traps each
year. For comparison, about 45 tonnes of rhenium are produced annually
worldwide. The scaled-up operation, says Kremenetsky should give them
their money back by the second year.
Right now the world's rhenium supply comes mainly from molybdenite, a
by-product of copper mining. The ores have to be roasted and the
rhenium extracted from the gas, which is a relatively time-consuming
and expensive process--the first gram of rhenium extracted by the
German chemists Ida and Walter Noddack in 1925 took a whopping 660
kilograms of molybdenite ore and cost $15 000 to produce. Production
methods have improved considerably since then, and the concentration
of rhenium in these ores is higher than in Kudriavy's volcanic gases. But
if it proves cheaper and easier to get the rhenium from this new source,
then it could be just what the engineer ordered.
"I can see five to ten years down the road there might be a real need to
recover the rhenium from that volcano," says Tom Millensifer of the
Illinois metals and minerals company Powmet, one of the bigger players
in the American rhenium market. "The need for rhenium is growing, but
the supplies aren't," he explains. The amount of rhenium produced these
days depends on the copper mines, several of which have closed down
in recent years. Meanwhile, demand for "superalloys" is going up,
primarily for use in aeroplane turbines, and rhenium has become an
essential component. Add a dash of rhenium to your metal recipe and
you get an alloy that has high strength at high temperatures, isn't brittle,
can be easily hammered into shape, minimises friction in a system, and
can be recycled thousands of times. With the high-tech industry
exploding, Millensifer predicts that demand for rhenium could very well
exceed the supply.
With such a buoyant market, other rhenium hunters have joined in the
search for volcanoes with valuable burps. Adams has had friends and
colleagues looking in Chile for another Kudriavy, but to no avail. If the
Russians pull it off, they may be the proud owners of the world's one and
only volcanic rhenium mine.
Still, it won't be easy. They'll have to ensure that their zeolites are not
clogged with chlorides and other metals, and somehow deal with the
changing landscape of an active volcano. While Kudriavy may not have
erupted since 1883, it still hiccups occasionally. Last year it blew a hole
30 metres across in the mountain top. The team would like to put in a
system of seismic monitors. In the meantime, says Solov'yow, "we hope
for good luck".
Most experts in the metal-mining world laugh a little when you bring up
the prospect of stuffing a cap over Kudriavy's head and sucking up the
rhenium. Not because it's a bad idea. But with the rotten-egg stench of
hydrogen sulphide belching out along with the volcano's treasure, at
temperatures of up to 950｡C and at pressures high enough to make the
belches roar and hiss, it might not be all that much fun. Adams shakes
his head over Steinberg's dedication to the burping volcano. "He's spent
most of his life up and down those islands," he says. "Rather him than
me."
Nicola Jones is a science writer based in Vancouver
From New Scientist magazine, 26 August 2000.
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