Monday, June 8, 2009

An Overview of Milling Uranium

Milling uranium is an energy intensive process. Even after the ore has arrived at the mill, massive energy is needed to mill the ore, to turn it into that desirable yellow cake. But don’t cut a slice just yet, and put down those candles.

An overview of the milling process will give you a better idea of what milling uranium entails as well as the quantities of chemicals involved. Calculating a mill’s carbon footprint (which should be mandatory for every new industrial project these days) needs to take a lot into account, including the heat used in milling, the transportation of ore and product to and from the mill, and the transport and manufacture of the chemicals used in the processes.

Throughout all of this, remember that the mill Energy Fuels is eager to build in Paradox Valley aims to process 1,000 tons (2,204,622.62 pounds – or about 143 large, African bull elephants) every day. That’s like grinding up 773 family cars, every day.

First off, though, the milling stages:

Grinding. You have to grind up the rock.

Pre-leaching & thickening. A fancy way of saying you need to treat the ground-up rock with acids, and then thicken the slurry.

Leaching. Add more caustic substances to the mix to dissolve the coveted minerals.

Uranium recovery. Precipitate the minerals with the addition of more chemicals.

Vanadium recovery. Repeat to get your vanadium oxides.

First, to grinding. Ore is dumped on stockpiles, shipped from area mines via truck. Using a front end loader, the rocky ore is lifted and dumped into a feed hopper. It is then fed via a conveyor to the Semi Autogenous Grinding (SAG) mill.

Here, the ore is combined with volumes of water, and tumbled with steel balls.

After tumbling to reduce particle size to around 0.03 inches, the slurry is ‘delivered’ to large, steel storage tanks, located outside the SAG mill. Then, more pumping, from the storage tanks to two rubber-lined steel pre-leach tanks. Now concentrated sulfuric acid (H2SO4) is sprayed in, to reduce the pulp density to 25% solids. (In other words, enough H2SO4 to be three-times the volume of the particles in solution. That’s a lot of acid.)

The slurry is then pumped to a 60 foot diameter, rubber-lined, steel thickener tank where the overflow is clarified, filtered, and sent to the feed tank for uranium recovery. The partially dewatered underflow is pumped into the leaching circuit to be re-concentrated.

Back in the SAG mill the slurry moves through eight tanks with agitators. Here the pulp is heated to 185ยบ F using steam. More H2SO4 is pumped in to leach out the uranium and vanadium minerals. Sodium chlorate is added as an oxidant, as needed. Wherever there is heat, there must also be pressure, so some emissions are necessary – or else the SAG mill would explode.

Now it’s time to separate the liquids and the solids, and purify the solution. The pulp is pumped to a series of 40 foot diameter ‘counter current decantation’ (CDD) thickeners. The ‘pregnant’ solution is separated from the solids, and pumped to the recovery feed tank. The solids, the tailings, are pumped into the tailings cells.

Then, in the Solvent Extraction Building (SX), extraction is performed to concentrate and recover the uranium. The solution is filtered, and the uranium is separated using a kerosene-based (as in oil and jet-fuel) solvent. This is then ‘washed’ with more H2SO4 and more water to remove impurities. Finally, the uranium is stripped from the kerosene-based solvent with sodium carbonate solution.

Now we move to the drying and packaging building, where the uranium is continuously precipitated from the stripping fluid by adding hydrogen peroxide. The yellow cake (triuranium octaoxide, (U3O8), uranium dioxide (UO2) and uranium trioxide (UO3), collectively known as ‘urania’) is partially dewatered, washed, filtered and dried in a steam dryer. Lots more heat. Lots more energy. Lots more byproducts.

Once dried, the yellow cake is packed and weighed in 55 gallon steel drums for shipment via the highway. Presently, each barrel (weighing around 900 pounds) is worth $44,100.00 to Energy Fuels. That’s not enough to be economically feasible. At current prices (of about $49/pound) the mill would generate daily revenues of $215,600.00. That’s still not enough. (Energy Fuels has spent more than $20 million in just researching the mill already.)

Finally, the drums of yellow cake are shipped to a conversion plant, to be made into uranium hexafluoride (enriched) and sent to market. There is only one conversion plant currently operating in the US, the ConverDyn facility in Metropolis, Illinois. There’s another in Ontario, and product can be shipped to Texas for processing overseas. But that’s still an enormous amount of gas used in transport. One estimate is 45 metric tons of CO2 per year just in transporting the milled ore to conversion. This doesn’t include shipping in the ore or the chemicals necessary for its processing.

But lets look at the tailings, too. Energy Fuels likes to point out that the tailings are not dangerous – after all, the majority of the uranium has been removed. If this was true, why are tailings so notoriously deadly around water wells? Isn’t kerosene bad to drink? Is it safe to bathe in concentrated sulfuric acid? You mean they’ve extracted 100% of the uranium they were concentrating? That’s amazing!

Anyway, the tailings piles will be state of the art, Energy Fuels is keen to observe. They will be lined with two 1.5 mm polyethylene (plastic) geomembranes. Not one, but two. (This is a vast improvement, apparently. In the old days they just dumped the waste into holes in the ground.) There is some leak detection system used that Energy Fuels has never been able to elaborate on, when asked. (It’s odd that they can’t answer that question on the spot, you’d think it would be a good one to know.)

Once full the tailings are covered with compacted soil and then an ‘erosion cap’ is placed on top. This is basically a kind of concrete. Then, they re-vegetate, hoping life will take hold (but not too tight, they don’t want root systems breaking up that erosion cap). The tailings only need to be engineered to provide 1,000 years of coverage, but leaks through the two plastic liners have occurred in the past. Just look at Canon City.

Basically there’s a lot more to this process than the presentations given by Energy Fuels elucidate. They’re fond of platitudes and overarching statements. One of my favorites is: “There have been a lot of changes in the milling industry. It’s like cars. A car today is much more advanced than a car of the 1940s.” Aside from mixing metaphors and admitting the previous incarnation of uranium mills were, sorry, terrible, this does little to present the data. It’s like walking into a bank and asking for a loan with “Give me a million dollars, I will repay it in time.”

Just as a banker wants to see a budget, any population that will be living beside a uranium mill deserves to be presented scientific, actual data. Not pie-in-the-sky rhetoric and patronizing reassurances. You would think these uranium pros would be over-brimming with technical data to share – heck, it’s their lives! If you talk to my friend Red about welding, watch out, you’ll get a tour of his truck! He can rattle off quantities of gases and materials that boggle the mind. But these guys come off as skirting the issue, repeating platitudinous metaphors as irrelevant as they are misleading.

I want to give these folks a chance to explain these “new technologies” that have “changed the industry” like never before. In fact, in Norwood last year, I cornered Energy Fuels President, George Glazier, and asked him for an example of this “new technology”. He revealed to me that one such example is the alarm on the storage tanks. When they get full, a light will go on which will show they’re full, so the slurry can be redirected. Wow, I thought. We’ve been doing that for years in the pipeline business. How can uranium – the futuristic, save-the-world science set to quash climate change – be so far behind? When pressed further he mentioned the leak detection in the tailings, but stopped short of explaining how it worked or what it was.

The way this works is the scientists who come to present the material don’t actually have the answers. They’re kinda’ like salesmen. So they give you a name for another scientist. But he (or she) can’t help because he (or she) doesn’t return calls.

In the end you get the impression no one really knows, or cares, because they’re too busy crunching future revenues, and juicy profits, to worry about the little things – like minimizing exposure to milling effluents. It’s odd, really. You’d think they’d jump at the chance to prove all this tech. Instead, it’s like hunting for a silhouette of truth in a room full of shadows.

Even if the uranium milling industry has improved immeasurably in the last 40 years, it’s hardly grounds for proving this mill. It’s like pointing to a cave from your tent and saying, “look how far we’ve come.”

Good luck weathering the storm!

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