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
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