Re: Radioactivity in fertilizer

["Bruce A. Busby" <bbusby@umich.edu>]

Perhaps some of my learned fellows can answer this better, but I did work 
for a while at a phosphate to fertilizer plant in Idaho, so I will take 
my shot at it. Some EPA reg person can answer that part of the question 
though.                                      

The ore enters the plant with about 17-32 percent phosphate of some type, 
is mixed with an acid such as Sulfuric. This allows the switching of ions 
and produces phosphoric acid. The phosphoric acid is mixed with various 
chemicals like ammonia to make the solid fertilizer, used straight as 
liquid, mixed with ammonium sulfate for a fire retardent, ect.

So, where is the radioactivity? Well, the good news is very little is 
actually transferred to the phoshoric acid, the bad news is most of it is 
either let off as gas (Po) or concentrated in the "gypsum" that is the by 
product of the acid vats. The gypsum is pretty much a hard rock like 
substance once dried, and has been uses in road construction, sidewalks, 
landfills, with a little problems.  Some places used it as a building 
material for house foundations, which adds to the radon load of the house.

So, I figure that some else can take it from here. Anyone have some 
numbers to through out.. levels, ect?

-Bruce Busby