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Sat Feb 4, 2017, 12:37 AM

An interesting inversion in the distribution of lanthanides, (RRE) in Kentucky coal ash.

In my position as a student and an advocate of nuclear energy I get to hear a lot of, um, what has come to be known as "alternate facts" although I still prefer the word "lie" to "alternate fact."

One of my least favorite "alternate facts" about nuclear energy is very popular in spite of being, um, delusional, is the one that goes "Nobody knows what to do with nuclear waste," even though I and lots of other people whose work I've read and studied know very well what to do with so called "nuclear waste." Lots of people know what to do with fission products and actinides, and it's not their fault that their critics are completely ignorant of their work and are just doing a Kelly Conway and "making stuff up." The treatment of used nuclear fuel has been the subject of study for more than half a century by some of the finest minds one can find.

I would submit that the first step in understanding "what to do with" so called "nuclear waste," is to recognize that nothing which is useful, in many cases, extremely useful can be considered "waste." For example, one of the world's great environmental problems among many great environmental problems, concerns halocarbons, chlorocarbons (including chlorofluorocarbons to be sure) which are a problem because of their long half lives and stability on a human lifetime scale, and worse, fluorocarbons, not just atmospheric varieties but also water born and living tissue born perfluorocarbons like PFOS and PFOA (respectively, perfluorooctanoyl sulfonate and perfluorooctanoic acid) and their analogues and degradants.

I would submit, if you look into it, that there is nothing that can break a carbon fluorine bond quite like gamma radiation, and an excellent source of gamma radiation is fission products.

But I'm not here presently only to complain about anti-nuke ignorance and stupidity, but to note some issues with a form of waste that, unlike used nuclear fuel which is remarkable only inasmuch as it hasn't killed anyone, to remark on a recent publication about a real form of waste with which nobody knows how to deal, coal waste.

Fossil fuels, especially coal, are responsible for the seven million deaths that take place each year from air pollution, and where air pollution deaths are concerned, coal's contribution is largely a function of particulates, which are often carbon particles that have reactive species like dibenzofurans, dibenzodioxins and a bunch of other nasty stuff.

But another function of the death and destruction and health impact of coal waste concerns the ash and fly ash, which often includes powerfully toxic volatile elements, the most famous of which is the neurotoxic element mercury, but also includes other toxic elements like arsenic and selenium.

The accumulation of coal ash is a very, very serious problem, involving billions of tons of waste, that leads to events like the Martin County coal slurry disaster which destroyed hundreds of miles of rivers, contaminated the water supply of 27,000 people and resulted in a fine of $5,600 levied by the wife of the asinine thug who now runs our Senate, rubber face gorgon himself, Mitch McConnell.

(If you look, you might begin to harbor suspicions about the role that coal based mercury plays in inducing insanity by comparing the map of the States carried by Trump with distribution of national coal plants. I'm not saying it's cause and effect, but it is an interesting speculation, now that mass insanity in the United States is on display for all the world to see.)

Anyway. Is coal waste really "waste?" I think it is, but that doesn't mean it's entirely useless. For instance, W. Alex Gabbard at ORNL in a rather famous article in the Oak Ridge National Laboratory Review pointed out that some forms of coal ash actually contain more energy content in the uranium present in the ash than was present in the original fuel.

This brings me to the lanthanides, which are often called the "rare earth elements" "REE" even though many of them are not really rare at all, although some are.

In general, many of the lighter lanthanides, lanthanum itself, cerium, praseodymium, and neodymium, are readily available, although the so called "renewable energy" industry, as well as the electric car industry are putting a certain amount of pressure on their supplies. The heavier lanthanides are somewhat rarer, and notable among the elements of concern are europium, used in phosphors for low energy lighting such as LEDs, and dysprosium, which is a component of very high quality magnets used in things like, um, "renewable" wind turbines. The wind industry has proved useless in addressing climate change, more or less, but would be even more useless without lanthanide based magnets, and dysprosium is very much an element of concern, in particular because the majority of the world's high quality lanthanide ores are enriched with respect to the lighter lanthanides (lanthanum through samarium) and depleted with respect to the heavy lanthanides (gadolinium through lutetium).

It was therefore with some interest that I read the following paper in the primary scientific literature in the current edition of the fun journal Energy and Fuels where you can find all kinds of people playing around with dangerous fossil fuels, biofuels, carbon dioxide and stuff like that.

The paper in question is this one:

Size-Dependent Variations in Fly Ash Trace Element Chemistry: Examples from a Kentucky Power Plant and with Emphasis on Rare Earth Elements (Energy Fuels, 2017, 31 (1), pp 438–447)

It's written by Chinese scientists - the world's most knowledgeable scientists where lanthanide chemistry is concerned are in China - collaborating with scientists in Mitch McConnell's home state. (That can't be pleasant, being a scientist in a state that elected Mitch McConnell.)

One of the major environmental problems with lanthanide processing, which despite the "green" label attached to so called "renewable energy" is separations, and one of the major separations that one seeks is to separate the heavies from the lights.

Apparently coal combustion can do that.

Some excerpts from the paper:

In general, the partitioning of trace elements in coal combustion is a function of the volatility of the elements, with low volatile elements, such as the rare earth elements (REEs, or REY if Y is included), Sc, Hf, Mn, Rb, Th, and Zr, being distributed evenly across bottom ash and fly ash (group 1 after Clarke and Sloss(1) and Meij(2)), intermediate volatility elements, such as Zn and As, which are enriched in fly ash relative to bottom ash (group 2), and the halogens, Hg, Se, and B, among the most volatile elements (group 3). Among other factors, the concentration of an element in fly ash depends first upon the element abundance in the feed coal then upon combustion conditions, the type of fly ash generated (such as the amount of carbon), the particle size and surface area of the fly ash, and the flue gas temperature at the point of ash collection.(1, 3, 4) Further discussion of trace element partitioning can be found in the studies by Martinez-Tarazona and Spears,(5) Vassilev and Vassileva,(6) Senior et al.,(7-9) Yan et al.,(10) Vassilev et al.,(11, 12) Karayigit et al.,(13) Narukawa et al.,(14) Li et al.,(15) Pires and Querol,(16) López-Antón et al.,(17) and Hower et al.,(18-20) among others.

In recent years, REEs in coal and coal combustion products (CCPs) have attracted much attention because (1) the rapidly grown demand for REY as a result of their wide applications as metal catalysts, permanent magnets, light-emitting diodes, batteries, phosphors, and various components for renewable energy equipment,(21-24) (2) the supply crisis of 2010 and the price spike of 2011,(25) which was caused by the export restrictions from China and initiated a treasure hunt by way of exploration for REY deposits all over the world,(26) (3) highly elevated concentrations of REY in some coals and CCPs that are comparable to or even higher than those in conventional economic deposits,(27, 28) and (4) preliminary REY extraction experiments (e.g., studies by Taggart et al.(29) and Rozelle et al.(30)) that showed that CCPs may be technically suitable as REE ores.


Some comments on the volatile elements in coal waste, including the toxic elements arsenic, selenium, lead and uranium, coal waste being a subject about which most people could care less, even thought they can wax stupid for hours about so called "nuclear waste," with used nuclear fuel being comparatively easy to contain since in more than half a century less than 75,000 metric tons of used nuclear fuel have accumulated, whereas billions of tons of coal ash have accumulated or been vaporized:

3.2.1Some Volatile Elements (As, Se, Cr, Co, Ni, Zn, Pb, and U)
The behavior of trace elements in the ash collection system at coal-fired power plants takes on at least three different modes of behavior. Trace elements, such as arsenic, are volatilized in the boiler and then captured by the ESP or baghouse fly ash.(32, 41-43) Figure 3 based on Table 6 in the study by Sakulpitakphon et al. (with one correction that the ESP 10/325–500 mesh ash has 1949 ppm of As and not 1494 ppm as published)(32) shows the distribution of As by the ash collection hopper and by mesh size within each hopper. Not unexpected, the As concentration is higher in the second and third row ESP hoppers than in the economizer and mechanical hoppers, a function of the lower flue gas temperature in the ESP hoppers. With the caveat that every coal and every unit is different and will produce different trace element distributions, this is in line with the increases from <100 ppm of As in the mechanical hoppers to 545, 703, and 1259 ppm in the first through third ESP hoppers in another unit burning eastern Kentucky coal.(42)...

....Other volatile elements, such as Se(18, 44) and Hg,(19, 32, 41, 42) exhibit more complex behavioral patterns. Mercury concentrations in fly ash, for example, are a function of not only the Hg (and Cl) concentration in the feed coal but also (1) the flue gas T at the point of collection, (2) the amount of carbon in the fly ash, and (3) the form of carbon...

...With respect to the U concentration in the same suite of sized fly ashes, it generally shows a similar negligible variation pattern as the REE, as mentioned below. Hower et al.(20) noted a particle-size-dependent trend toward higher U in finer sizes in both the mechanical fly ash and in the second row ESP fly ash. Because the mechanical fly ash is coarser than the ESP ash, the variation in the U concentration in the ash sizes influences the overall U concentration...


And now to the interesting point:

The REEs do not show significant variation between rows of ash collection systems. With re-examination of the Ce data from the Mardon and Hower study,(42) no definitive trend in Ce variation was observed between the rows. The LREE/HREE, however, decreases from the economizer and mechanical rows to the third ESP row. Considering the fly ashes in this study, while the Ce content generally does not vary significantly between rows or between particle sizes within the individual hoppers, for the <200 mesh ashes, LREE/HREE decreases with a decrease in the particle size.

The decrease in LREE/HREE from 7.15 in the economizer hopper to 4.74 in the ESP hopper is a function of the relative LREE/HREE of the size fractions within each fly ash. The 100–500 mesh economizer ash fractions, accounting for over 78% of the ash, range from 6.93 to 7.79 LREE/HREE. In contrast, the <500 mesh fly ash, with a light LREE/HREE signature, comprises 96% of the ESP fly ash.


This graph below shows the distribution of lanthanides in particles of various sizes:



In every case, the graphs show distributions that look quite different than those found in worked ores including the most economically important today, those in China.

Of course, these coal ash particles are not really "ores" since they are still dilute when compared to mineral sources of the elements. While it might be economic at some point to extract the uranium, if only because the extremely high energy to mass ratio associated with uranium which is responsible for its environmental superiority to all other forms of energy, this is probably not the case with things like wind turbines, which have an extremely low energy to mass ratio, which accounts in part for their poor performance in arresting climate change.

Have a nice weekend.

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