The problem of Russia's resources of rhenium-a silvery- white transition metal with a very high melting point and very ductile-was discussed in our magazine on two recent occasions, in No. 3, 1999 and No. 4, 2000. As was pointed out by an expert in the field, Alexander Kremenetsky, Dr. Sc. (Geol. & Mineral.), of the Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Earths of the RF Ministry of Natural Resources and Russian Academy of Sciences, the country has practically no deposits of this strategic raw without which aerospace physical metallurgy is unthinkable. The situation can probably be remedied to a certain extent by a recently discovered new source of this metal - an active volcano by the name of Kudryavy on the Island of Iturup in the Kuriles. Its high-temperature gas discharges contain rhenium in high concentrations (1.5-5.1 g/g).

As Dr. Alexander Kremenetsky points out, the estimated resources in the above area amount to 20 t/year which is more than enough to meet Russia's needs for this strategic material in the 21st century. But in the opinion of Vladimir Znamensky, Cand. Sc. (Geol. & Mineral.), of the RAS Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, who visited the Kudryavy Volcano with a prospecting party when they discovered there considerable quantities of rhenium disulfate, the high-temperature ores from this volcano and its steam-and-gas emissions cannot be put to industrial uses for reasons of what he called an aggressive environment. In his view they are nothing but a material for studies by volcanologists, mineralogists and geochemists. Some time later the OBSHCHAYA GAZETA newspaper (No. 36, 2000) carried an article on the subject by Vladimir Pokrovsky, which we now reproduce in an abridged form.

Several days ago a unique experiment was launched on the Russian Island of Iturup in the Kuriles. Experts working on the Kudryavy volcano there are setting up the world's first pilot plant for extracting rhenium from volcanic gases...

The unit looks like a small pyramid, erected next to the crater, and needs no permanent crew. Technical crews will be coming and going about once a week to check on the plant's condition and retrieve the accumulated rhenium.

The really impressive thing about the project is that the producer plant is located right on top of the "supply" volcano and the method of mining, or extraction, is a far cry from the traditional. The main suppliers of rhenium, mainly from Latin America, are now on their guard because, if everything goes as planned in Russia, the price of the metal can drop by some 50 percent (it now stands at 1,400 US dollars a kilo) which will upset the world rhenium market...

The Kudryavy is not an active volcano with its last eruption registered back in 1883. But it is alive and kicking, to use the expression, with jets of white and hot volcanic steam

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constantly streaming up from the fumarole fields around the crater. By escaping into the atmosphere from a depth of several kilometers they help reduce the pressure in the subterranean "furnace", preventing its overheating and eventual eruptions. The Kudryavy "coughs" only from time to time when all of its vents are flooded by heavy rains. The last such "fit" occurred in October 1999.

The steam-gas jets from around the Kudryavy have a temperature of +600 to +900 ⁰ C, something that makes this volcano a truly unique and lavish "treasure trove". As Dr. Alexander Kremenetsky points out, it is only at such high temperatures that volcanic emissions carry with them to the surface rhenium and scores of other precious metals, including gold. According to current assessments the local fumarole fields contain some 20 tons of rhenium sulfate.

Dr. Alexander Kremenetsky says the original idea was to mine the mineral by open-cut methods. But in view of a small size of the deposit, which would have been quickly exhausted, our Institute suggested a method of extraction directly from the gas-steam mixture. It has to be blown through a zeolite layer which is a good absorbent, especially at high temperatures. And then by "rinsing" the zeolite column with a weak acid solution the metal could be extracted by means of standard technologies.

Bearing all these things in mind, the experts decided to follow the example of the Egyptian Pharaohs... and started building a pyramid. And the "edifice" does not have to be of some rare rocks, but of timber because of the highly aggressive local environment which ruins metal structures near the crater in no time. Timber has much better chances of survival; but for an industrial unit even logs will most likely have to be replaced with glass or concrete.

Thus, the experts engaged on this project are facing two problems: to prove that their technology will really "deliver" rhenium on an industrial scale and, second, to make sure that the venture will not end in yet another natural calamity of some sort. As for the latter, the experts are more or less at ease.

"We are not going to build a factory on the volcano," assures Dr. Kremenetsky. "The plant will be absolutely 'uninhabited' with the personnel residing a safe distance away and visiting the site only now and then to adjust the equipment."

The new "daredevil" technology of rhenium extraction from top a volcano has already caught the eye of foreign volcanologists and mineralogists. Other countries, too, could do with some of this rare metal... And even despite the skepticism expressed by many Western experts concerning this "extravagant" and "risky" business, rhenium hunters are already on the look-out climbing some local volcanoes. And they found one in the Hawaii, but its steam-and-gas jets turned out to be much cooler than on the Kudryavy.

The pilot experiment on the Kudryavy will be completed in a matter of some 40 days when a 100-kilo container with the precious raw will be ready for shipment to Moscow where experts will pass their final verdict.

Prepared by Vladimir GOLDMAN

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