Metal Oxide Sorbents for the Separation of Radium and Actinium

[NNadir]

(Note: This post, and many of my earlier posts in this space, contains some graphics which may not be accessible to Chrome users because of a recent upgrade to that browser, but should work in Firefox and Microsoft Edge. When my son has time, he will adjust the file system for a website he's building for me to make these graphics usable in Chrome, but he seldom has that much time on his hands. Interested parties, should they exist, can still read my posts including the graphics, but regrettably must use a browser other than Chrome. Apologies - NNadir)

The paper I'll discuss in this post is this one: Metal Oxide Sorbents for the Separation of Radium and Actinium (M. Alex Brown Ind. Eng. Chem. Res. 2020, 59, 46, 20472–20477)

One of the more interesting things about anti-nukes is the deep abiding concern they show for uranium ore tailings - which contain radium, most of which is Ra-226, the natural decay product of uranium-238, with a nearly vanishing fraction consisting of radium-223, from the uranium-235 decay chain.

On the other hand these same anti-nukes are spectacularly disinterested in a much larger source of radium that is associated with flowback water from natural gas fracking operations, particularly in the Marcellus Shale, which is a uranium formation. The same process that extracts natural gas, also extracts radium, and the flowback water is dumped right on the surface, with very little effort to control it, any more than there is any effort to contain the dangerous combustion combustion waste of dangerous natural natural gas, dangerous carbon dioxide.

Anti-nukes couldn't care less about dangerous natural gas, of course, since without access to it, the so called "renewable energy" industry would be exposed for the scam it has always been when the lights, refrigerators, theaters, home, public and surgical all go dark because the wind isn't blowing and the sun isn't shining. The Trump scale lie that's told about this crime against the future, burning natural gas, is that it's "transitional."

This is absurd, since the use of dangerous natural gas has continuously been growing at a vastly faster rate all through this century. (This is in terms of energy and not the often disingenuous and fraudulent appeal to peak capacity without reference to total capacity utilization, which for wind and solar is absurdly low, and thus materially wasteful, this while having no relation to demand.)

I have argued that the uranium (and thorium) already mined is sufficient to provide all of humanity's energy needs for centuries, at least in "breed and burn" scenarios, many of which are ready for commercial application, and thus uranium mining is not really necessary, and arguably will never be necessary again, at least in a world where attention to risk and the environment, and the facts of engineering are not subjects of derision and contempt, both on the political right and quite frankly, on the political left as well, albeit with different foci.

Because air pollution kills millions of people every year, and because the death toll from extreme heat is rising dramatically, the death toll associated with nuclear operations - which is clearly non-zero - is trivial compared with all other forms of energy. Nuclear energy, where it operates, saves lives. The argument that any or every nuclear death to which excessive attention is paid excuses millions of other deaths not associated with radioactivity which are ignored is not merely stupid; it is unethical in the extreme. It is in fact, equivalent that the two deaths at Bengazi outweigh the hundreds of thousands of Covid deaths, an argument the Republican party unashamedly makes much to the disgust of the entire civilized world.

Nuclear technology saves lives in other ways, most famously associated with medicinal use, both in imaging and in therapy and sometimes in the combined practice known as theranostics.

Radium-226, which has a half-life of about 1600 years, can be transmuted, in a neutron flux into the rare element actinium-227, which has a half-life of 21.77 years. This is the only naturally occurring actinium isotope that is present in large enough quantities in natural sources (uranium ores) to be isolated, but doing so is extremely expensive. Actinium-227 is too long lived to be of much use in medicine, although it would be an excellent fuel for a thermoelectric generator in bulk quantities, but the isolation of radium from either uranium mine tailings or flow back water itself is fairly expensive.

There has been a lot of interest however in another isotope of actinium, Ac-225, which has a half life of ten days and which is a powerful alpha particle emitter. Since alpha particles do not travel very far in matter, this means that any destruction associated with interaction with matter is highly localized, something that is clearly desirable in for instance, cancer treatment using an expedient like an ADC, an antibody drug conjugate, where the antibody has a CDR (complementarity determining region) associated with cell surface displays unique to cancer cells.

This paper is about Ac-225.

From the introduction:

Targeted alpha therapy utilizes the ionizing capabilities of alpha-emitting radioisotopes to treat a variety of infectious diseases and cancers, particularly prostate and bone cancers.(1,2) A promising candidate is 225Ac and its short-lived daughter product 213Bi alongside a potent alpha/beta cascade.(3) In aqueous solution, the stable trivalent valence of Ac3+ leads to a number of potentially useful bifunctional chelators that when conjugated to a targeting vector can drive the isotopes to various biological targets.(4) Consequently, large-scale production is under development by the Department of Energy’s Isotope Program and the National Isotope Development Center (NIDC), which currently produces 225Ac by high-energy proton spallation of thorium targets or aged stocks of 233U/229Th.(5−7) New production channels are being investigated including 226Ra(γ,n)225Ra → 225Ac, 226Ra(p,2n)225Ac, and 226Ra(n,2n)225Ra → 225Ac, all of which could potentially utilize up to 100 mg or more of a natural radium target.(8−10)

Regardless of the production channel and as 225Ac is scaled toward curie quantities, it must be considered that increased alpha dose rates could detrimentally affect the chemical processing of the targets and products. The separation of Th targets, Ra, Ac, and fission fragments have been executed using commercial ion-exchange and extraction chromatography resins.(11−14) However, the alpha-destructive nature of irradiated Ra and Ac can incur radiological damage on conventional organic/silica-supported resins.(15) It is well documented that mCi quantities of these isotopes (particularly Ra and subsequent daughter products) can effectively destroy such resins to the point that in some cases the material can no longer be recovered from a column.(16−20) The estimated daily dose of 20 mCi 225Ac (including daughter products) to 100 mg of cation-exchange resin is 2 × 108 cGy.(21) The reported absorbed dose threshold of cation-exchange resins is 108 cGy, after which diminished performances have been observed.(16) Further, curie quantities of 225Ac will certainly degrade polyvinyl supports and introduce organic impurities that could contaminate the product and ultimately affect chelation chemistry.

There may be advantages in using metal oxide sorbents (frequently used in high-performance liquid chromatography)(22) considering their high radiation stability and widespread application in the recovery and purification of fission 99Mo...(23)

...The focus of this work was to investigate if inorganic-based normal-phase sorbents can be used as a platform to retain selected +2 and +3 cations—starting with Ba and La nitrate surrogates then onto to 228Ra and 228Ac tracers.(30)

In this case, the authors isolated Ra-228 from aged isolated thorium using solvent extraction procedures with a TOGDA complexing agent. Radium is a decay product of the thorium decay chain as it is in uranium-235 decay chain. Radium-228, which has a half-life of 5.75 years, decays by beta emission to Ac-228, which has a half-life of about 6 hours. Thus this system is a surrogate for the production of Ac-225 by either Ra-226(n,2n)Ra225 -> Ac-225 reactions or Ra-226(p,n)Ac-225 reactions.

To model this system, given the difficulty of isolating Ac-228 and Ra-228, Barium/Lanthanum was used to model these reactions. The authors then attempted separation using metal oxides.

Some pictures from the text showing some results:

Separations on titania and alumina, the oxides respectively of titanium (as marvelous TiO2) and aluminum:



The caption:

Figure 1. Partition coefficients of La (purple diamond solid, [La]0 = 0.5 mM) and Ba (blue circle solid, [Ba]0 = 0.9 mM) on alumina and titania from HNO3 at room temperature. Uncertainties were derived from ICP–MS analysis.

The caption:

Figure 2. Partition coefficients of La (purple diamond solid, [La]0 = 0.5 mM) and Ba (blue circle solid, [Ba]0 = 0.9 mM) on alumina, titania, and zirconia from 0.20 M acetate at room temperature. Uncertainties were derived from ICP–MS analysis.

The surrogate barium/lanthanum system:



The caption:

Figure 3. Elution of La (purple diamond solid, [La]0 = 0.8 mM) and Ba (blue circle solid, [Ba]0 = 1.4 mM) from zirconia at room temperature using 0.20 M acetate and HCl at a flow rate of 2.0 mL/min. Resin mass = 1.0 g and column diameter = 1 cm. The elution curves serve as a visual aid.

The real thing:



The caption:

Figure 4. Elution of 228Ac (orange diamond solid), 228Ra (blue circle solid), and 212Pb (green triangle up solid) from zirconia at room temperature using 0.20 M acetate and HCl at a flow rate of 2.0 mL/min. Resin mass = 1.0 g and column diameter = 1 cm. The elution curves serve as a visual aid.

The caption:

Figure 5. Activity measurements of the HCl (pH 1.0) product solution in Figure 4 containing 228Ac (orange diamond solid) and 212Pb (green triangle up solid). The solid lines represent the half-lives of 6.15 and 10.6 h corresponding to 228Ac and 212Pb. Uncertainties were derived from counting statistics.

It is important to note that all of the radioisotopes mentioned in this paper occur naturally. When one fissions a naturally occurring nuclide, either as a transmutation product (Th-232 -> U-233 or U-238 -> Pu-239) or U-235 which occurs naturally, one eliminates all future members of the decay series. Although used nuclear fuel is highly radioactive owing to the short half-lives of most fission products, it can be shown, that in roughly 1000 years of continuously recycled nuclear fuel, the total radioactivity associated with nuclear fission energy will actually be lower than the natural radioactivity contained in radioactive ores of uranium and thorium. (This may or may not be a good thing.)

The conclusion of the paper:

A number of metal oxide sorbents were evaluated as radiation-resistant platforms for the purification of highly alpha-active Ra targets and 225Ac using surrogate elements and isotopes. It was demonstrated that alumina, titania, and zirconia are capable of fractionating Ba and La from dilute acids and in the presence of an acetate buffer—La was much more strongly retained than Ba. Titania was able to retain both Ba and La at pH 6, and alumina exhibited appreciable degradation below pH 4. Zirconia was chosen for a set of stationary column elution profiles and proved effective in both Ba/La and Ra/Ac separations, where the final product was recovered in dilute HCl. Notable differences in the elution behavior of Ba/Ra and La/Ac were observed. The chosen pH of an acetate feed for the separation of Ba/La was 5.1 followed by a pH 2 HCl La recovery. For Ra/Ac, a pH of 4.1 acetate was used to remove Ra followed by pH 1 HCl to recover Ac and Pb. The radiometric purity of the 228Ac product indicated good decontamination from the 228Ra parent. These results suggest that zirconia could be a feasible platform for the separation of bulk Ra targets for the purification of 225Ac.

Despite the rising Covid-19 numbers, I trust you will be safe and well and able to enjoy the many wonderful privileges of being alive. I wish you the happiest of Thanksgivings!

[Arne]

1. Thank you for this.

[CatLady78]

2. Did you watch "Planet of the Humans" NNadir?

I haven't seen it as it was pulled off of youtube before I could. It was generally panned.

I wondered if there was some overlap between your criticisms of the renewable fuel industry and theirs. They probably dissed nuclear energy too though.

I did like that they mentioned human overpopulation. Some sort of horrible blend of dominion theology and the most mindless kind of capitalist drive for more consumers at all costs, has made it "anti-human" to point out the obvious, even as we drive most non-human species to extinction.

If people on the left don't raise this issue, neo-nazis and far right tribalists across the world will be the only ones who do....it is so obvious to me that a 100 years down the line, this will be the rightist take on "green". We can't keep calling decent environmentalists/scientists- David Attenborough, Paul Ehrlich, Michael Moore etc. ecofascists for pointing out the obvious.

This is why I did not want a kid. Personal choice of course. But all of us at least should not rapaciously gobble up all of the planet. Some of us have got to take one for the team....Having fewer children should be recognized as a form of community service.

Advocacy for smaller families is hardly forcible sterilization. Like wearing masks or other eco-friendly choices (less meat, less consumption), it is an unselfish choice you make that so clearly benefits the planet. It is just not being recognized as one...

Of course it would be counterproductive to diss people for large families (i.e. > 2-3 kids). That just sets people's backs up since we are not yet evolved enough to see it as a selfish decision. But for those open to the idea, to frame having fewer kids as a positive contribution you could choose to make for the planet and society, might have more traction.

[NNadir]

3. No, I haven't seen it; I was not even aware of it.

One is seeing more and more criticisms of so called "renewable energy" now that the reality of this nightmare is coming home to roost.

Even someone as stupid as the anti-nuke pundit Benjamin Sovacool is beginning to get it, although his attachment to this chimera now includes mining undersea mineral formations, destroying the oceans with the same enthusiasm he shows for destroying terrestrial ecosystems and wilderness. (I don't consider him a scientist even though somehow he gets published in major scientific journals; his Ph.D. thesis from UVA is amusing as hell; it consisted of taking a poll of energy executives, some of whom remained anonymous.)

The reality is that so called "renewable energy" is not renewable, since it's energy to mass ratio is appallingly small and it requires two systems to do what one can do. (LCA & MFA for so called "renewable energy" seldom includes the economic and environment cost of the inherent redundancies required, including the pernicious toxic nonsense dreaming about batteries.

As for population; one hears this a lot as a kind of catch all phrase for all environmental issues. I don't fully credit this. I have argued that an ethical way to have addressed this problem would have been to meet human development goals: Population grows more slowly, and birth rates fall below the replacement rate in places where people can be secure in their homes and whence they are well provided with food, shelter, medical care, and the free flow of information. The embrace of human development goals would have been an ethical way to bring the population of the planet closer to its carrying capacity. As it is, the carrying capacity of the Earth has been vastly over extended, and the result will probably be population reduction via catastrophe, with the end carrying capacity being much lower than it was before it was over reached.

There are two kinds of people who vote for the likes of Donald Trump, those who are badly provided for and have nothing to lose, are badly educated, and those who lack a shred of concern for humanity and ethics and are only interested in personal acquisition. (All of these people must be racists or extremely tolerant of racism.)

I do not consider Michael Moore to be an environmentalist in any way. I have heard that he is coming around on so called "renewable energy" but otherwise, I regard him as an appalling fool, badly educated, glib, and prone to vast overestimation of his own morality.