Understanding Phosphogypsum and Phosphogypsum Stacks

• Phosphogypsum is an industrial by-product in the production of phosphate fertilizer from naturally occurring phosphate rock.
•  1 ton of phosphoric acid produces about 5 tons of phosphogypsum.
• Phosphogypsum is considered toxic and radioactive. 
• Globally, 15% of world phosphogypsum production is recycled while the remaining 85% is disposed of without any treatment. Specifically, use of phosphogypsum in the U.S. is limited due to the 1989 ban and 1992 modification of the ban on its use by the U.S. Environmental Protection Agency. Other countries, such as India, Australia, Brazil, and Spain, recycle it for use "as building materials, agricultural fertilizers or soil stabilization amendments and as set controller in the manufacture of Portland cement."
• In instances when it is not recycled, miners stack it into mountainous piles, or stacks, next to the plant/factory.

Phosphogypsum Stacks in Florida, U.S.

• There are more than 20 phosphogypsum stacks in the vicinity of Lakeland and Tampa in the U.S.
• Environmental groups have documented 11 gypstack failures between 1994 and 2016 in Florida, including pollution of the Floridan Aquifer in August 2016, when 215 million gallons of acidic water and phosphogypsum was disgorged into it through a sink-hole.
•  The Mosaic Company is the “biggest phosphate company in the world and a major presence in Florida, mining phosphate rock on more than 70,000 of the 380,000 acres it owns in Manatee, Hillsborough, Polk and Hardee counties.”
• Most Floridians never see the stacks because they exist far away from the beaches and theme parks.
• The perception of the Mosaic Company to the local inhabitants in Florida is one of preferred and top employer and generous donor to local projects.

Phosphogypsum Stacks in Zelzate

• The phosphogypsum stack located on the boundary of the municipalities of Zelzate and Ghent, in Belgium, covers approximately 65 hectares and the total volume of phosphogypsum is estimated to be 18 million tons.
• The groundwater and leachate of this stack are assessed every 6 months, and as of 2018, the value of radioactivity parameters in the leachate have significantly decreased due to the rehabilitation and development measures for the stacks implemented since 2010.
• The Federal Agency for Nuclear Control (FANC) in Belgium also continues to follow the issue of the soil contamination outside of the stack within the perimeter of the old production units.
• Studies caution that if conversion of these former phosphogypsum stacks for construction purposes (whether residential houses or workplaces) should occur, there could be a significant exposure to the radio active gas, radon, if no precaution against its infiltration is taken during the construction.

Encapsulation of Phosphogypsum Stacks

• "Encapsulation technologies have been used to passivate reactive minerals by depositing non-reactive minerals as surface coatings (e.g., silica encapsulation of pyrite in mine tailings), either by injection of appropriate reagents or by more thorough mechanical mixing. "

• "Examples of successful phosphogypsum encapsulation have not been found."

Summary of Findings

• From our preliminary research, we were able to determine that information on the phosphogypsum stacks in Florida is readily available, while that of Zelzate is relatively available. We were unable to find publicly available information for analysis on the phosphogypsum stacks in Le Grand Quevilly, except a mention that had a highly developed phosphate industry in the early 1990s.  
• Further, from our research, we were unable to find any publicly available information on projects on encapsulation of phosphogypsum stacks in Tampa/Florida, Zelzate, and Le Grand Quevilly. Available information does not show such projects in Tampa. Additionally, a report prepared for the U.S. Environmental Protection Agency notes that "successful phosphogypsum encapsulation have not been found." In Zelzate, the stack is monitored and may be considered for construction of buildings in the future.
• We suggest a pivot on the research as detailed below: