Separation of Uranium from Lanthanide (Rare Earth) Ores.
Last edited Mon Feb 11, 2019, 05:03 AM - Edit history (1)
The paper I'll discuss in this post is this one: Selective Removal of Uranium from Rare Earth Leachates via Magnetic Solid-Phase Extraction Using Schiff Base Ligands (Laurence Whitty-Léveill醇, Nicolas Reynier†‡, and Dominic Larivière*‡ Ind. Eng. Chem. Res., 2019, 58 (1), pp 306–315).
In two previous posts in this space, I discussed the properties of the element cerium, one of the 14 (15 if you count yttrium, 16 if you add scandium) lanthanide or rare earth elements.
Polymers of Cerium and Plutonium.
Cerium Requirements to Split One Billion Tons of Carbon Dioxide, the Nuclear v Solar Thermal cases.
In the latter post, I pointed out that there is not enough cerium in the world to reliably split even a minor fraction carbon dioxide released each year while we wait like Godot, for the "Green New Deals," "Gazillion Solar Roofs," "Energiewende..." ...blah...blah...blah...blah...programs to slow climate change which, even as people around the world have thrown trillions of dollars at them, have failed, completely and totally, to have any effect on climate change.
They haven't worked, they aren't working, and they won't work. The reason is physics.
They, schemes centered on so called "renewable energy" nonetheless remain very popular, which goes to show you that very often - this should be very obvious - what is popular is neither good, effective, realistic, or remotely honest.
In rhetoric, the fallacy underlying this sort of situation is known as the bandwagon fallacy, which is a feature widely exploited in advertising, since it is not true that the "Best selling car," is actually a good, reliable or safe car, or that the "best selling nutritional drink" is good for you, or that "the best selling acne treatment" is effective at treating acne, and so on.
In my tenure here at Democratic Underground going back to 2002, I've had a lot of very unpleasant interactions with people embracing this fallacy, the sort who like to point out that somewhere a huge bird and bug and bat grinding wind farm is being built somewhere while elsewhere a nuclear plant is being shut.
I have always struggled against my own stupidity in many ways and sometimes - not always, but sometimes - I have succeeded in overcoming it: Here, I've learned to use the wonderful "ignore" button to avoid interacting with the preternaturally stupid people who are different from me only in that they are satisfied with their stupidity, revel and wallow in it, assert it as a positive good, and are proud of it. The person currently described as the "President of the United States" is famously such a person, but there are many other examples of similar people and frankly - I say this as a life long Democrat who has always voted Democratic, even at some pain - we have examples of such people in our party, and in fact, on this website. We all know them here and elsewhere, at work, at school, in our neighborhoods, even if we never turn on the TV to watch words drool out of the criminal babied orange fool who has described himself as a "real stable genius."
Anyway...
Despite the advertising success of so called "Renewable Energy!!!!!" - a brand name that is itself a lie since this form of energy is neither "renewable" or sustainable because of the low energy to mass ratio involved in the devices to collect and store it - the degradation of the planetary atmosphere is accelerating: The rate of increase has now reached an average of 2.3 ppm per year.
Even if you can sell electric cars by putting pictures of solar cells in the ad, or wind turbines, or both, here is what it says on the Mauna Loa Carbon Dioxide Observatory website as of this writing:
Week beginning on February 3, 2019: 411.63 ppm
Weekly value from 1 year ago: 407.81 ppm
Weekly value from 10 years ago: 386.99 ppm
Last updated: February 10, 2019
The type of data reported here, by the way, is one of 2,245 such data points recorded and posted by the Mauna Loa Carbon Dioxide Observatories website, going back to 1974. The increase over the same date of the previous year, 3.82 ppm, is the 29th largest ever recorded. Of the top 50 such data points, 32 have been recorded in the last 5 years, 37 in the last ten years, and 40 in this century.
We have no realistic plan to stop what we are doing to all future human beings, and in fact, all future living things, because we cannot do what Abraham Lincoln told the country to do in other, far less deadly and dire circumstances, "think anew."
I have deliberately macerated the following text to take it out of the context of the American Civil War and an address to congress, to choose the phrases that appeal to any generation faced by seemingly insurmountable tragedy, and let's be clear, that the risk Lincoln faced, the destruction of the United States and its government is an inconsequential think when compared to the destruction of the planetary atmosphere:
...Fellow-citizens, we can not escape history. We... ... will be remembered in spite of ourselves. No personal significance or insignificance can spare one or another of us. The fiery trial through which we pass will light us down in honor or dishonor to the latest generation...
...We shall nobly save or meanly lose the last best hope of earth.
This text is always on my mind, not just because of the history of the American Civil War, but because of how the same ideas apply to climate change.
I steal that beautiful locution, "last best hope of earth," all the time, taking it far out of any context Lincoln could have known, to describe nuclear energy.
This brings me closer to the scientific paper referenced at the opening of this post.
My previous post in this space referenced above, the one about cerium as a carbon dioxide splitting catalyst, contained the following text, repeated here for convenience, since ores is referenced in the paper under discussion.:
Neodymium in neodymium iron boride magnets is often utilized in generators, including those in bird and bat grinders in the sky, a.k.a. wind turbines, marketed as being "green," even though they are no such thing. Neodymium is not really a "rare" element, and the common locution (with which I'm not comfortable) "rare earth" does not apply. It cannot be called a common element either; there are limits to how much can be recovered, and in any case, its recovery is environmentally onerous as I noted previously in this space:
Some life cycle graphics on so called "rare earth elements," i.e. the lanthanides.
Magnets utilizing dysprosium are somewhat superior to neodymium iron boride magnets, but more expensive. Probably the locution "rare earth" applies better to dysprosium, the main source of which is the less common mineral (compared to monazite and Bastnaesite), xenotine.
The external costs of isolating lanthanide elements is higher if the device running them spends a lot of time off line, put another way, if the capacity utilization is lower. The capacity utilization of wind turbines in most locations typically falls into the range of 30%-40%, meaning that 60% to 70% of time, the lanthanides in wind turbines do nothing. When they do nothing, power companies burn dangerous natural gas these days. Nuclear plants, by contrast, routinely run at better than 90% capacity utilization.
The paper discussed refers to the fact that in many cases lanthanide mine tailings are radioactive. (I have long been familiar with the radioactive thorium (and decay daughter) content of lanthanide ores, but the fact that lanthanide ores contain uranium as well, and, of course, all of its radioactive daughters is somewhat new to me. One learns something every day, if one is lucky.)
From the paper's introductory text:
The presence of naturally occurring radioactive materials (NORM), including U and Th, in these minerals is problematic from both a regulatory and health physics perspective for the mine operator.(4,5) Thus, effective methods to separate NORM from valuable REE constituents are essential.(6) While most of the short-lived decay products from Th- and U-series, such as Ra, Pb, Po, and Bi, could be segregated from REEs as they exhibit different chemical behavior during acid leaching and separation steps,(7) the separation of naturally occurring actinides from lanthanides still needs to be addressed.
Numerous strategies have been published to segregate U/Th from REE leach liquor. As an example, Sadri et al. recently reported that precipitation through pH adjustment followed by selective redissolution could be applied to REE leach liquor to isolate U, Th, and REE in distinct fractions.(7) However, these steps require precise pH adjustment and multiple phase separation to obtain the proper level of separation. Zhu et al. also reported that the combination of solvent extraction, selective dissolution and ion-exchange resin could be used to purify REE fractions from U/Th impurities.(6) However, this separation strategy, in addition to being cumbersome, generates significant volumes of radioactive acidic liquid wastes.
In the paper the authors describe a process whereby uranium can be removed from lanthanide ores by the use of ligands attached to magnetic particles. This type of process, widely utilized in analytical chemistry, of which it is a key component, as well as in some large scale processes, is called "solid phase extraction."
In this case, the solid phase particles are iron oxides supported on silica, "Fe3O4@SiO2."
Quoth the authors:
However...
The general scheme of what they propose is suggested by this cartoon from the paper's abstract:
The authors set out to address this lack of selectivity by covalently known organic extraction ligands showing selectivity to lanthanides and actinides to the magnetic particles. They have the following structure:
The caption:
The selectivity of these ligands can be controlled by the size and geometry of the binding sites.
Appealing to in silico modeling the authors explore the use of substitutents on the basic system, where the "R" designated groups, as is customary in the organic chemical literature refer to "wild card" function groups that can be attached.
The caption:
Scheme 2. General Structure of the Schiff Base Family Ligands and Its Coordination of the Uranyl Ion
Substituents on the phenyl rings (R1–R4, R1′–R4′ ) are freely modified and may be used for easy control over the ligand properties.
Exploring the ligand structures from "Scheme 1" the authors identify the uranium capacity for these derivatives.
The caption:
They evaluate the effect of ions that may commonly be found during the extraction processes used to isolate lanthanides from ores because of the high strength acids used to dissolve them, and the adjustments to the pH of the system that may be required:
The caption:
"Qe" in the ordinate of this graph refers to the binding capacity.
The kinetics of the reaction are not incredibly fast:
The caption:
One can imagine that this might be adjusted by adding excesses of the magnetic particles, or perhaps using an industrial flow system, should this technology ever come to industrial scale.
But the big issues is selectivity.
It's actually quite good, showing the ratios (the distribution coefficient) of the various elements captured by the particles.
The caption:
The authors conclude:
Most of the world's lanthanides come from China, but occasionally China threatens the rest of the planet with export bans. This raises interest in opening mines in other countries, including both the United States and Canada.
The mining leachate used in the experiments here were Canadian in origin, and besides uranium, contained in higher concentrations other elements, including lead, thorium and cadmium.
Lanthanides are, by the way, common fission products found in used nuclear fuels and this separation technique could conceivably be modified for nuclear fuel reprocessing should we ever get serious about climate change, which we currently not even close to doing.
I have convinced myself that the only serious approach will involve mostly the recovery of uranium and thorium, as well as neptunium, plutonium, americium and curium from used nuclear fuels.
Under breeding conditions, the uranium and thorium already mined - the latter residing mostly in lanthanide mine tailings - are sufficient to shut every oil well, every gas well, and every coal mine on the planet for centuries.
I trust you're having a pleasant Sunday afternoon.
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