Refining Uranium by the PUREX Process

PUREX is the major chemical technique for recovering uranium from spent nuclear fuel. Based on the highly-selective extraction of uranyl nitrate from aqueous solution by tributyl phosphate  (TBP) in a nonpolar organic solvent, the technique is straightforward for home chemists to exploit in order to refine their personal uranium stockpiles.  The photo illustrates the supplies used in the following procedure: nitric acid, tri-n-butyl phosphate (from QualityBiological.com), Kleen-Strip 1-K kerosene (Home Depot), and 4.8 g of homemade uranyl oxide.

Caution: the PUREX procedure involves intimately contacting nitric acid with highly-flammable organic material!  Work with small quantities.  Concentrated acid will form explosive oils, so always dilute it to 6M or less.  This discussion presupposes essential safety understanding of the chemicals and techniques involved.

New Crusher for Uranium Processing

Time to kick it up a notch in the uranium kitchen, since I got tired of crushing ore solely by hand with a hammer.  The new equipment to turn big rocks into very small rocks consists of a three-inch jaw crusher made by Al Yates, coupled to a 3.75-horsepower Briggs & Stratton Model #094202 gas engine.  To match the engine’s 3600 RPM at full throttle down to a safe speed at the crusher cam (and store some rotational energy for particularly resistant rocks), a 1.75″ pulley is used on the engine shaft and a heavy 11.75″ cast-iron pulley on the crusher shaft (both from McMaster-Carr).  The belt is a standard A50 size.  The whole deal is mounted on a wooden base.

This crusher can produce about 15 kg (a two-gallon pail) per hour of fine rock flour from 1-3″ Utah uranium ore.  It would take many tedious days to accomplish this with a hammer, seives, and a ball mill.  Now the slow step in my artisanal mining and processing scheme is acid leaching, and the attendant gravity filtration of sediment in the leachate.

Coming up soon…a look at the PUREX process—solvent extraction of uranyl nitrate into an organic phase.

Hand-Cranked X-Rays

A hand-cranked Wimshurst static generator, coupled with a modern-production “magnetic effect” Crookes tube, can produce just enough x-rays to make useful digital radiographs and excite Geiger counters.  The Wimshurst machine and the discharge tube can be readily obtained from online retailers in educational science apparatus for as little as $120.  To make radiographs, I employed a 6-inch fluoroscopy image intensifier tube with a custom mount for my Canon S3 IS digital camera.  All photos in the following gallery were 15-second exposures with moderate hand cranking.

Magnetic-effect tubes contain a slotted cathode that allows a beam of electrons, formed in a high-vacuum glow discharge, to impinge upon a phosphor screen at near-anode potential.  In the classic usage, the experimenter observes deflection of the electron beam when a magnet is brought near the tube.  The only contemporary American manufacturer of a magnetic-effect demo tube, Electro-Technic Products Inc., was enjoined from offering the product on the domestic market precisely because of x-rays.  So tubes of this type available in the US are invariably of Chinese or Indian manufacture—all the better because they’re cheap.  I bought mine from www.sci-supply.com for $79.95.

So what’s the possible utility of this?  Radiography in third-world outposts with no electrical supply?  Hardly…the image quality is too poor, 15 seconds too long for practical exposures, and ever since the vacuum tube went the way of the dinosaur it’s been easy to get enough power from batteries to energize small, intense, pulsed cold-cathode x-ray machines.  But the novelty factor is nice, and in museums or other didactic settings, the literal hands-on nature of this x-ray apparatus should be appealing.

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Fingers of a 28-year-old male hominid.  This hominid’s other hand was busy cranking the Wimshurst to power the tube for the exposure.  Field uniformity is poor, and the source-to-detector distance is a mere six inches–but contrast is OK and this is a perfectly serviceable human radiograph.  Exposure was approximately 100 μR.

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PVC and polyethylene hoses of the same size (left and right, respectively), vividly illustrating the x-ray attenuating power of the chlorine in PVC.

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Electronic stopwatch. Decent detail, including individual wires, can be discerned.  Remember, the x-ray source is a Crookes tube, not a modern line-focus x-ray tube!

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Iodine tincture (a few percent iodine in alcohol) from the drugstore is black to x-rays.

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Geiger tube from a CDV-700 civil-defense Geiger counter.  Prominent features visible by x-ray include the thin beta window in the middle of the tube’s active region, and the thin anode wire running down its axis.

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A hand tap set contained in a plastic box. No big surprises, but the taps are slightly magnetized and some resulting warpage of the image-intensifier output can be seen.

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The handle of a cheap steak knife, showing how the blade is anchored into the plastic.

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Package of “AA” lithium batteries.

Nuclear Collection (Part III)

Radioactive chemical reagents (and a bit of non-radioactive fake yellowcake) constitute this instalment of my Nuclear Collection feature.

Depleted uranium metal from United Nuclear. These two rough-hewn triangular slabs weigh in at about 13 g apiece.  No idea what Bob Lazar cut up to put these on the market, but they’re not a bad deal while they last. They sport very rough, sharp edges and have to be stored under oil because of the risk of pyrophoric ignition.  Uranium fires are a bummer, especially when they occur in your living room.

Fake yellowcake memento from the Conquista Project.  About 20 cm³ of a canary-yellow, non-radioactive powder that resembles a diuranate salt is contained in a small vial embedded in this commemorative plastic paperweight.  The Conoco-Pioneer strip mining and milling operations in Karnes County, Texas commenced in 1971, for a time producing most of that state’s uranium.

Real yellowcake, or actually a chemically-pure grade of depleted U₃O₈ in a 1-lb reagent bottle from Research Organic /Inorganic Chemical Corp.  After calcining, this is indeed what most modern “yellowcakes” resemble both in chemistry and appearance.  This bottle is a gift from Tim Koeth, builder and operator of the beautiful 12″ cyclotron at Rutgers University.

Uranyl acetate reagent bottles, also from Tim Koeth.  Uranyl acetate is still widely available as an electron-microscopy stain.  It’s a beautiful color, and like most uranyl salts, exhibits striking UV fluorescence.  The yellow crystals have a faint odor of vinegar.  Likely they taste accordingly (although taking uranium internally is generally frowned upon).

Vial of urea labeled with 50 microcuries of carbon-14.  C-14 is a weak beta emitter that is best known for its role in carbon dating.  Because of the importance of carbon in biological processes (durrrh!), C-14 is also useful as a tracer in research, which is the suspected purpose of this product from New England Nuclear.  The label says “Use only as authorized by Atomic Energy Commission,” effectively dating this carbon to 1974 or earlier.  Activity is only detectable by removing the lid and holding a Geiger tube over the opening.  A gift from Tim Koeth.

Calibrated bismuth-210 beta sources. Bi-210, or archaically “radium E”, appears in the uranium decay series.  The sources actually contain lead-210 (radium D) with a half-life of 22 years in secular equilibrium with the 5-day Bi-210 daughter.  The weak betas from Pb-210 are absorbed in the source, while the 1.2-MeV betas from Bi-210 are free to escape.  The set is incomplete; present are four sources ranging in activity from 7.73 nCi to 0.364 μCi (measured in 1962).  A gift from Tim Koeth.

Quarter pound of thorium nitrate. This bottle of Baker ACS-grade reagent is still sealed, preventing radon from escaping and allowing the delicious thorium decay chain to build up.  The penultimate thorium decay product, thallium-208, is responsible for one of the most energetic gamma rays found in nature: 2.62 MeV.  I use this bottle as a source of 2.62-MeV gamma radiation to calibrate the high end of the energy scale in scintillation spectrometry.

Cheap Chinese Induction Coils

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The induction coil, once an essential tool of modern physics that lay behind the discovery of the electron, x-rays and radio, has been relegated to the toybin.  Most of the modern ones are made in China like the rest of our toys.  While the coils of yore were mahogany-cased artisanal masterpieces destined for the most prestigious laboratories, today’s product is pitched at the Wal-Mart Shopper: sloppy mass production and everyday low prices.  I recently bought one such coil for use in an outreach program at Albuquerque’s Explora museum.  Billed as a 60-kV Ruhmkorff coil, the same product seems to have several outlets in the US.  This is a quick review.  Click below for more…