About Radioactive Material from Fertilizer Production
Phosphate rock contains the mineral phosphorus, an ingredient used in some fertilizers to help plants grow strong roots. Phosphate rock contains small amounts of naturally-occurring radionuclides, mostly uranium and radium. When processing phosphate rock to make fertilizer, the phosphorous is removed by dissolving the rock in an acidic solution. The waste that is left behind is called phosphogypsum. Most of the naturally-occurring uranium, thorium and radium found in phosphate rock ends up in this waste. Uranium and thorium decay to radium and radium decays to radon, a radioactive gas. Because the wastes are concentrated, phosphogypsum is more radioactive than the original phosphate rock.
The waste that is created during fertilizer production is stored in large piles called stacks. Some stacks cover hundreds of acres and are hundreds of feet high. In the aerial photo, you can see that the top of a phosphogypsum stack is covered in water.
Phosphogypsum is very watery when it is first put on the stack. As the phosphogypsum dries out, a crust forms on the stack. The crust thickens over time, reducing the amount of radon that can escape and helping keep the waste from blowing in the wind. Some of the water can leak out the bottom and pollute local groundwater.