For anyone who hasn’t already seen the news, a Mosaic Phosphate fertilizer plant in Florida, in Polk County, had a 40 ft diameter sink hole open up and swallow one of their “phosphogypsum stacks” I.e. a waste product pond full of gypsum byproduct from phosphate rock processing went down a natural sinkhole and back into the earth, and since Florida is a honeycomb of Karst rocks, into the groundwater. That Karst structure with dissolving rocks is, BTW, why they get sinkholes… Now you might ask just what the rock is that is dissolving, but I’ll leave that for another day. Though a bit of clue comes from the phosphate mine being right next to the drained ‘pond’ / stack, and that they mine phosphate rocks from between carbonate strata…
OK, this concerns me. Polk County was basically where I lived, fished, hung out, etc. most when in Florida. Fishing is good in the various ponds left behind by phosphate mining. I drank that ground water, and will again. So what is this “radiation” that’s gotten into the ground water and just how much ought I panic? That’s the question.
Oh, and a bit of chemistry. They dig up a Calcium Phosphate natural rock, crush it, add sulphuric acid, and get out phosphoric acid (used for fertilizers and in prior times laundry soap, though now that use is largely forbidden due to it also fertilizing wherever the city put your waste water and causing algae to be very happy…) This leaves Calcium Sulphate, that is also known as Gypsum. The white chalky stuff the drywall in pretty much all our homes is made from. Unfortunately, there is way more of it made than needed for wall board, and the natural gypsum has lower natural radiation levels, so this “phosphogypsum” mostly just piles up on it’s way to becoming a new gypsum rock deposit. Or eroding to return to the ocean from which it came when Florida was underwater a few tens of thousands of years ago.
My First Thought
My first thought was WTF is radiation doing at a fertilizer plant? Are they talking about K40? Bananas are radioactive due to the potassium 40 in them. I am radioactive for the same reason. So are you.
Well, it was only partly that. Partly too was that the phosphate rock they mine has some Radium, Uranium, and Thorium in it. Not really a surprise as sea water has those in it, and so do the sands from the mountains that make the monzanite sands of The Carolinas, Georgia, and down to the Florida coast. Nice sources of “rare earths” and Thorium. The decay products of U and Th also make basements without good ventilation a not-very-good-idea over much of that area too.
So ok, there’s U, Th, Ra and the breakdown product Rn Radon kicking around the place, and some of it ends up in the gypsum… somehow. Is it enough to be a worry? I go digging… but not in the phosphate mine…
Comes From, Goes To, Sizes
Things I always want to know about “stuff” and “data”:
Where’s the ‘comesouta” and the “goesinta” and how big is the flow?
All bolding, unless otherwise noted, done by me.
This article is about a plant in India, so we can assume the worst, with zero EPA oversight and few environmental standards. The Mosaic plant ought to be much better.
Natural radioactivity assessment of a phosphate fertilizer plant area
S.K. Sahu, P.Y. Ajmal, R.C. Bhangare, M. Tiwari, G.G. Pandit,
Environmental Monitoring and Assessment Section, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
Received 17 October 2013, Revised 1 January 2014, Accepted 2 January 2014, Available online 22 January 2014
Open Access funded by The Egyptian Society of Radiation Sciences and Applications
Under a Creative Commons license
Rock phosphate ore processing and disposal of phosphogypsum contribute to enhanced levels of natural radionuclides in the environment. The concentration of naturally occurring radionuclides in soil, rock phosphate and phosphogypsum samples collected around a phosphate fertilizer plant were determined. Also the external background gamma levels were surveyed.238U, 232Th, 226Ra and 40K activities in soil samples were 21–674 Bq/kg, 11–44 Bq/kg, 22–683 Bq/kg and 51–295 Bq/kg respectively. The external background gamma radiation levels in the plant premises were ranging from 48 to 133 nGy/h.
Rock phosphate; Phosphogypsum; TENORM; Radium equivalent activity
Phosphate rocks of sedimentary origin contain Uranium (238U), Thorium (232Th) and its decay products in addition to phosphate minerals (Roesseler, 1990). Considerable variations are found in the chemical composition of rock phosphate from different mining areas. In general, sedimentary phosphate rocks, or phosphorites, originated in a marine environment, are characterized by activity concentrations of uranium much higher than those of volcanic and biological rocks. Reported values of 238U in rock phosphate range from 1.0 to 5.7 Bq/g (Barisic et al., 1992, Guimond and Hardin, 1989 and Heijde et al., 1988). These phosphates are largely used for the production of phosphoric acid, fertilizers and hence phosphate fertilizer industries are considered to be a potential source of natural radionuclide contamination. Their radioactivity leading to health problems from radiation at the level of the industrial processes which involves mining and transportation of phosphate ores and production of fertilizers. At the usage level, when fertilizers dispersed into the geo and biospheres, have a potential to transfer to living beings. Leaching of the minerals and wastes is another potential source of radioactivity dissemination which may contribute to enhanced exposure of workers, public and the environment to these radionuclides.
Phosphogypsum is a waste by-product from the processing of phosphate rock by the ‘‘wet acid method’’ of fertilizer production, which currently accounts for over 90% of phosphoric acid production. The wet process is economic but generates a large amount of phosphogypsum (5 tons of phosphogypsum per ton of phosphoric acid produced)
3. Results and discussion
The levels of naturally occurring radionuclides (238U, 226Ra, 232Th and 40K) in soil samples are given in Table 1. The 238U activity in soil samples varied from 21.5 to 674.5 Bq/kg and that of 226Ra was ranging from 22.8 to 683.7 Bq/kg. At location 7 (gypsum pond) 226Ra values were found to be considerably higher than 238U, which is consistent with the nature of elemental distribution during chemical processes resulting in the generation of phosphoric acid. During acid attack of rock phosphate to produce phosphoric acid, majority of uranium along with thorium get partitioned with phosphoric acid while the radium, which follows calcium chemistry, finds its way with phosphogypsum (Poole, Allington, Baxter, & Young, 1995). The levels of 238U and 226Ra in soils at the two locations (location 4 and 7) were about 10–30 times higher than the rest of the plant locations and the average Indian soil levels of 20 Bq/kg. The open storage of such high radioactivity material could affect the surrounding in various pathways like emanation of 222Rn, atmospheric transport, leaching, dissolution and transport to aquatic environment (Bolivar et al., 1995). Activity concentration of all the nuclides except for 40K, were found to be maximum at location 4, at the Rock Silo, where phosphate rock is stored in large quantities. This is due to the fact that raw materials containing phosphorus show low activity concentrations of 40K but have significant activity concentrations of radionuclides belonging to 238U chain (Serena, Patrizia, & Luigi, 2005).
Gee… the majority of the radioactivity at a plant is in the rock INPUT to the process. The U and Th tend to end up with the phosphoric acid product, while the radium ends up in the gypsum. OK, so avoid the rock pile… which came out of the ground… where the ground water is percolating…
The article goes on with a fairly detailed and painful mapping of where there is how much of what. All nice to know, and yes, the gypsum pond is also hotter than ‘background’ at the natural surface, but not by all that much, and less than the natural input rock in the rock pile.
Radiation and Phosphogypsum
• Both natural gypsum and phosphogypsum contain radioactivity, but phosphogypsum contains more.
• In the manufacture of phosphoric acid, the acid is filtered through cloth to remove solids. The radium is filtered out with the solids. The solid portion is known as phosphogypsum.
• Phosphogypsum produced in North Florida contains roughly 5 – 10 picocuries per gram (pCi/g) of radium while phosphogypsum from Central Florida contains about 20 – 35 pCi/g radium.
• The U.S. EPA prohibits the use of phosphogypsum. An exception is made for phosphogypsum with an average concentration less than 10 pCi/g radium which can be used as an agricultural amendment. EPA’s ban was based on a single scenario which assumed that the by-product was used in road building or as an agricultural amendment and 100 years later a house was built on the farm field or the abandoned road and the homeowner lived in the house 70 years, staying in the house 18 hours a day. Under this scenario the homeowner’s risk of radon-related health concerns only slightly exceeded the EPA’s acceptable limits.
• Phosphogypsum is primarily calcium sulfate, and plants need the sulfur it contains. Since much of the North Florida phosphogypsum is below the EPA restriction level, it can be used as a crop amendment, but for no other use.
• The Central Florida phosphogypsum is restricted to storage on land in large piles called “stacks.”
• The overall radioactivity in the stacked phosphogypsum is actually less than what was in the original phosphate ore that was taken out of the ground.
OK, so this gypsum ‘stack’ (which is in Central Florida) is about 2 x 3 times the level that can be used to grow food… and if you are a prisoner in a home built on top of it, kept there for all but 6 hours a day, and live to 70 years old, you might, might be able to find some health impact base on EPA paranoid levels of concern.
The “stuff” is less radioactive than the rocks dug out of the ground under the plant, and through which the present ground water percolates.
It “moves with calcium” so will tend to bind into the rocks just like all the other calcium (which is likely why it was in the rocks to begin with).
IF it gets diluted by a factor of 2 or 3 as it runs into the huge ground water flows under Florida, it gets back to that “ok to put on food” level.
Somehow I’m not seeing much of a problem.
Though I’m pretty sure there will be panic all over central Florida, the EPA will be grandstanding and looking for ways to shut down phosphate production in the USA, the news will be endlessly Panties-In-A-Bunch about RADIATION!!!! in the groundwater of Florida, and a gazillion dollars of lawsuits will be filed.
Oh, and note that the quantity found in the soils and rocks in the first study were from 20 Bq/kg in clean soil up to a few hundred Bq/kg in ‘dirty’ places. Gee, that must be a lot..
China set standards on granite countertop materials, banning the export of
lower radiation level granites. They grade granite countertop material into four
grades : A, B, C, and below C. Only grade A can be used inside a home.
Grades B, C, and below C are allowed to be exported or used outside of homes
Finland 300 Ra bq/kg th 200 bq/kg 40K 3000
Latvia Residential interior use or Ra + Th 170 bq/kg 40K 1500 bq/kg
Industrial or exterior use residential ra + Th 250 bq/kg 40 K 2000 bq/kg
Industrial exterior or road use ra + Th 300 bq/kg 40 K 2500 bq/kg
Germany radium 226 levels below 300 Bq/Kg
Luxembourg Th less that 250 Bq/kg radon less than 350 bq/kg
Czech republic action level 150 -200 bq/kg for buildings occupied 1000 hrs or
more advisory level is 80 to 120.
Sweden says less than 200 Bq per cubic meter and gamma 0.5 uSv/h building
materials must be considered in the amount.
Nordic countries radium 300 thorium 200 40K 3000
Israel .5msv radium 150 thorium 185 40 K 3500
Oh… about as much in your granite counter top…