Reply #170: #2: Iodine can be recovered and contained, but is it worth it to do so?

[NNadir]

There are many insoluble iodides and iodates. Here is a list of some of them and their solubility products, which as chemists know, are very small numbers for essentially insoluble compounds:

Barium iodate: Ksp = 1.57 X 10^(-9)
Copper (I) iodide: Ksp = 1 X 10^(-12)
Lanthanum iodate: Ksp = 1 X 10^(-11)
Lead iodide: Ksp = 7.9 X 10^(-9)
Silver iodate: Ksp = 3.1 X 10^(-8)
Silver iodide: Ksp = 8.3 X 10^(-17).

Here’s a cool one, mercury (I) iodide, Ksp = 4.7 X 10-29.

If one has not wasted one’s college career attending campus anti-environmental Greenpeace rallies instead of doing one’s Chemistry 1 homework, one may be able to use this last figure to calculate how much water would be required to dissolve one gram of mercury (I) iodide. (To do this one needs to be reminded that the mercurous ion is actually dimeric, having an overall charge of +2, meaning that the formula for mercurous iodide is actually Hg2I2.) One can show that the amount of water to dissolve 1 gram of Hg2I2 is over 6.7 million liters. Moreover of this one gram, assuming that all of it was radioactive I-129, (which is actually not very likely) only about 38%, or 380 milligrams (0.38 grams) would actually be represented by I-129. The rest would be mercury. As I showed in post #167 (#1 of this series), the amount of radioactivity represented by this iodide that one would get from drinking 6.7 million liters would still be trivial. The mercury would probably kill you first.

This suggests an interesting use for the iodine produced in nuclear reactors: Sequestering the mercury that rains down on our heads minute after minute, day after day, 365.24 days a year, 10 years a decade, ten decades a century without let up. I have just posted in post #169 a link to some rough numbers on the amount of mercury released into the environment by coal processing and coal burning each year in the United States: About 200,000 pounds, which translates into civilized units as about 90 MT per year. Now, even though scientifically illiterate Greenpeace twits spend nowhere near as much time addressing the real danger of mercury, which actually kills, maims and otherwise injures people, as they do representing a “danger” of so called “nuclear waste,” which has actually killed no one, it actually happens that mercury is a very serious problem.

It is therefore a valid question to ask how much mercury can be sequestered by nuclear generated iodine. A reasonable estimate for the amount of all the iodine produced in nuclear reactors for the entire history of commercial nuclear power worldwide, I-127 (non-radioactive) and I-129 (long lived radioactive) inclusive, is roughly 60 MT, of which more than 2/3, or more than 40 tons, is the radioactive isotope. If one does a little stoichiometry one sees that, even if one could somehow capture all of the mercury released by coal use in the United States, all of the world’s nuclear generated iodine would just be to sequester even a year’s worth of US coal related mercury releases. (It happens, that irrespective of what “clean coal” liars tell you, trusting in your credulity, it is actually not feasible to capture “all” of the mercury released by coal burning and processing. And even if they do capture it, all they do is dump it somewhere, and probably not, one guesses as an insoluble iodide.)

Of course, were one to use mixed iodine isotopes from spent nuclear fuel for this purpose, one would actually have to recover it. This is certainly technically feasible. However as I noted in post #159 (#2 in the series on Iodine risks), the Purex process that is now commercially used to reprocess nuclear fuel allows for the release of I-129 to the environment. Over 2 metric tons, or 5% of the I-129 generated, has already been released into the environment and has been distributed worldwide. As I noted also in post #159, this iodine accounts for about one in every three billion iodine atoms found in the Mississippi River today. But then I showed in post #167 (#1 in the present series) that the risk of this iodine is actually less than one forty millionth of the risk associated with the potassium in our bodies, some of which is also radioactive. This raises an important question. Is it worth it to capture I-129 at all?

People do not often actually think too much about the costs of risk mitigation, since everyone seems to operate under the tacit, albeit ridiculous, notion that every life has infinite worth. Still there is fantasy and then there is the real world. Let us assume that it takes ten million dollars a year to install and operate iodine scrubbers on the world’s Purex reprocessing reactors. Let us also assume in the absence of any real evidence that this is actually the case, that the tiny amount of radioactivity associated with the release of I-129 to the environment actually causes the death of one person per year somewhere on the planet. Then the cost of saving this life is ten million dollars. Now, I fully recognize that among the scientifically illiterate Greenpeace twits, one life lost to a causation related to nuclear technology is worth millions of lives lost to other forms of pollution, but I am not addressing scientifically illiterate Greenpeace twits. Instead I am addressing reasonable people. How many lives can be saved by the use of ten million dollars a year for the purpose of extending health benefits to uninsured children?

I ask again, is it really worth it to remove one slightly radioactive atom out of every three billion from the Mississippi River?