Phosphogypsum, Bone Valley's Moonscape

Phosphogypsum is an industrial byproduct of the phosphate mining and fertilizer manufacturing processes found in Northern and Central Florida, Louisiana and Mississippi. A majority of its production occurs in our Bone Valley. The late Richard Coleman, Bone Valley Issue Co-Chair and a former Director of the Florida Institute of Phosphate Research, asked Dr. Paul Clifford, Executive Director of FIPR, to write an article on phosphogypsum dealing with radioactivity, heavy metals, etc. As of now, there is no substantial, allowable use for phosphogypsum and we must understand its real properties so that some solution can be found. Phosphogypsum stacks represent a potential groundwater pollution hazard and are an aesthetic blight - just stacking it in Polk County is not acceptable.

The following is Dr. Clifford's article:

PHOSPHOGYPSUM BACKGROUND INFORMATION:

Phosphogypsum is a byproduct of the manufacture of phosphoric acid. It is produced when phosphate rock is treated with sulfuric acid to produce the acid. The phosphoric acid is then used to make fertilizer.

Approximately 30 million tons of phosphogypsum are produced in Florida each year. It is stored in stacks which range up to 200 feet in height and cover up to 400 acres. There currently are between 800 million and a billion tons of phosphogypsum stacked in Florida.

Chemically, phosphogypsum is calcium sulfate (CaSO4). It is identical to gypsum which occurs naturally throughout the world. All naturally occurring gypsum contains some impurities and the impurities differ from location to location. Similarly, gypsum produced from phosphate fertilizer manufacturing contains some impurities.

The impurities in phosphogypsum which cause the primary concern are radioactive materials. Uranium occurs naturally along with phosphate rock in Florida. Radioactive decay transforms uranium into other elements such as radium, polonium and lead. As a result, all of these radioactive materials are found in phosphogypsum.

These materials make phosphogypsum slightly radioactive. Phosphogypsum in Central Florida typically has a radioactivity level averaging about 26 pCi/g. Northern Florida phosphogypsum is less radioactive with typical levels about 10 pCi/g. By comparison, Portland cement, a common construction material, has a radioactivity level virtually identical to that of Northern Florida phosphogypsum. Ordinary construction bricks are about half as radioactive as Northern Florida phosphogypsum. Thus, 2 ordinary bricks are as radioactive as one Northern Florida phosphogypsum brick and 5 ordinary bricks are as radioactive as one Central Florida phosphogypsum brick.

Phosphogypsum contains several other impurities. One of the impurities is acid left over from the manufacture of phosphoric acid. Other impurities include low concentrations of heavy metals.

Although it is presently an unwanted byproduct, phosphogypsum has numerous potential uses. The Florida Institute of Phosphate Research (FIPR) has demonstrated that it is an effective road base construction material. Economic analysis has shown that use of phosphogypsum in a road base could significantly reduce road construction costs. In this use, it would also decrease the need for digging environmentally undesirable borrow pits.

Phosphogypsum can be used as a soil amendment to increase yields of fruits, vegetables and forage. Preliminary research has shown that it can be used as a daily cover in landfills to keep garbage from blowing around and reduce odors. In this use, it may be able to increase the capacity of landfills by up to 40%, thereby increasing the life of existing landfills and decreasing the need for construction of new landfills.

Sinkhole in IMC Agrico's New Wales Gypsum Stack - photo from Save our Springs Inc

In spite of these possible uses, there is little use of phosphogypsum at present. With one minor exception, E PA has banned the use of phosphogypsum. The EPA ban is based on EPA's concern about the radioactivity of phosphogypsum.

EPA calculated the risk to the public and workers from exposure to the radioactivity emitted from phosphogypsum. For road building, for example, EPA evaluated 8 different modes of exposure. It found an excessive risk in only one case. In that instance, EPA assumed that a road right of way would be abandoned some time in the future (e.g., in 100 years) and that a house would be built on that abandoned right of way. The agency also assumed that this house had no floor and a person would live in the house for 70 years and stay in the house 18 hours a day. Under these circumstances, EPA calculated that the risk was too high and banned the use of phosphogypsum.

FIPR has requested that EPA give it and Polk County an exemption to the ban in order to build a test road using phosphogypsum. FIPR and Polk County have agreed to EPA's request that the road right of way carry a deed restriction which would prevent building a house on the right of way. FIPR also conducted a series of site specific risk assessments specified by EPA. Each of these risk assessments showed the risks to be acceptable by EPA criteria.

The request for an exemption is now being considered by the Florida Department of Environmental Protection (DEP). DEP may be concerned about leaching of heavy metals. However, previous environmental studies on a road constructed with phosphogypsum before the ban went into effect showed that heavy metal leaching is not an environmental problem. In addition, tests conducted using an EPA approved leaching procedure show that heavy metal leaching will not be a concern.

Issue Chair Marian Ryan commends this site for its information about phosphate The Phosphate Risk