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Science Corner: Phosphate Mining’s Mark On Florida

Aerial view of Mosaic-New Wales' south stack and north stack, both more than 360 feet high.
Aerial view of Mosaic-New Wales' south stack (left) and north stack (right), both 360+ feet high. Image captured via Google Earth, 7/31/2023.

by Cheyenne Canon, Program Project Coordinator

Phosphate refers to several naturally occurring minerals that contain phosphorus. It is mined to extract phosphorus, one of the chemical elements that is a building block of life and is one of three primary ingredients in all fertilizers. Most phosphate mining in the U.S. occurs in Florida, especially in Central Florida, with one additional mine located in North Florida. These mines, both active and inactive, cover 450,000 acres, according to the Florida Department of Environmental Protection.

Putting aside the direct damage of mining activities to the environment, processing phosphate to produce fertilizer also creates a dangerous byproduct: phosphogypsum. Phosphogypsum (pronounced Fos-Fo-Jip-Suhm) is created when an acidic solution is used to dissolve phosphate rocks into a usable form of phosphorus called phosphoric acid. The waste product is calcium sulfate (or gypsum) which contains radioactive uranium and thorium that decay to become radium, which decays more to become radon, a radioactive gas. This process also creates a significant amount of waste—for every ton of phosphoric acid yielded, five tons of phosphogypsum waste is also created.

Because it is radioactive, this waste must be disposed of in a particular way to reduce its impact on people and the environment. To start, a liner is placed on the ground in the area where the waste will be stored to help prevent any leaching into the soil and groundwater. Then phosphogypsum is “stacked” in large, stepped piles, with the top of the stack slightly recessed, lined with plastic, and filled with untreated process water left over from other steps in the manufacturing process. The side of the stack will dry out and form a “crust” that helps to block the emission of radon gas.

An industrial dragline digs up and disposes of the first 15 to 30 feet of soil, then it digs out the phosphate-containing material to be processed.
A dragline digs up and disposes of the first 15-30 feet of soil, then it digs out the phosphate-containing material to be processed. Photo from People Protecting Peace River, Inc.

Florida currently has two dozen of these stacks and they each pose a significant threat to human health and the environment. You may recall news articles from back in 2021 regarding a leak at the Piney Point phosphogypsum stack. A significant amount of rainfall caused this stack to near 100% capacity and created a tear in the liner, leading to a leak. To prevent local contamination, 215 million gallons of the process water were diverted and released into Tampa Bay. This successfully relieved pressure at Piney Point but has since been linked to red tide outbreaks in and around Tampa Bay. The nutrient rich water is a veritable feast for the algae that form red tides. While this particular stack was unique in how under-managed it was, the same risk is present at all stacks. Their mere presence in a state which is prone to extreme flooding and sinkholes, and which has shallow freshwater aquifers where most Floridians get their drinking water, is a dangerous combination.

The solution to handling all this toxic waste is still uncertain. At least one company has been developing a new processing technique for the last decade that would eliminate the creation of phosphogypsum waste. However, the process involves intense heat, which would require more energy input and doesn’t address the destruction caused by surface mining. In Piney Point, officials are working to permanently close down the facility by building a deep injection well, which is expected to dispose of the process water in a confined saltwater aquifer 3,300 feet underground. Another “solution” recently approved by the Florida Legislature in HB 1191 is to study the use of phosphogypsum as a road base material. But opponents say the bill is a corporate handout, allowing billion-dollar companies to eventually sell their toxic waste to transportation departments while taxpayers foot the bill for it and for the original study required by HB 1191.

Save the Manatee Club’s Fertilizer-Free for Manatees campaign focuses on the use and consequence of fertilizers in Florida, but it’s clear that the consequences of their use span their entire life cycle—from mining phosphate to feeding algae blooms. Reducing the excessive use of fertilizers is the only sustainable solution.

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