- Ca5(PO4)3X + 5 H2SO4 + 10 H2O → 3 H3PO4 + 5 CaSO4 · 2 H2O + HX
- where X may include OH, F, Cl, or Br
Marine-deposited phosphate typically has a higher level of radioactivity than igneous phosphate deposits, because uranium is present in seawater.
In the United States
The United States Environmental Protection Agency has banned most applications of phosphogypsum with a radium-226 concentration of greater than 10 picocurie/gram (0.4 Bq/g). As a result, phosphogypsum which exceeds this limit is stored in large stacks.
Florida has a large quantity of phosphate deposits, particularly in Bone Valley region. However, the marine-deposited phosphate ore from central Florida is highly radioactive, and as such, the phosphogypsum by-product is too radioactive to be used for most applications. As a result, there are about 1 billion tons of phosphogypsum stacked in 25 stacks in Florida (22 are in central Florida) and about 30 million new tons are generated each year.
Various applications have been proposed for using phosphogypsum, including using it as material for:
- Health Physics Society. "Answer to Question #629 Submitted to "Ask the Experts"." Posted on February 9, 2001. Last accessed June 19, 2007.
- Florida Institute of Phosphate Research. "Phosphogypsum and the EPA Ban." Last accessed June 19, 2007.