""New and innovative process wastewater management and treatment methods to treat process water at gypsum stack systems can significantly reduce the environmental and economic liabilities posed by these systems by (a) reducing the inventory of process water capable of spilling into waters of the state; and (b) substantially reducing the costs of treating and disposing of process water when a gypsum stack system is closed. FIPR's process water technical advisory committee is an ideal forum through which new ideas on process water management and treatment can be scientifically evaluated."

Phil Coram
Chief
Florida Department of Environmental Protection
Bureau of Mine Reclamation

Process Water is the water used in the chemical process that turns the phosphate that is mined into the phosphoric acid that is used to make fertilizer. The wet process manufacture of phosphoric acid as practiced in Florida requires a large volume of process water that is used as a water source for phosphoric acid, gas scrubbing, transporting the phosphogypsum produced in the process to storage, operating barometric condensers, and a multitude of other uses in the chemical complex.

A major portion of the heat released in the process ends up in the process water and is lost to the atmosphere by evaporative cooling in the ponds. Process water is stored both in ponds on top of the phosphogypsum stack and in a below-ground level pond (cooling pond). The pond water is recycled back to the processing plant after it cools.

If heavy rains threaten to overflow the ponds or if an operating plant is shut down and it is necessary to close the phosphogypsum stack and pond water system, the water must be treated before it can be discharged. Process water is acidic, with a low pH of about 1 to 2, and contains a dilute mixture of phosphoric, sulfuric, and fluosilicic acids. It is saturated with calcium sulfate and contains numerous other ions found in the phosphate rock used as a raw material as well as ammonia from the solid fertilizer manufacturing process.

The volume of water in the pond system that would need to be treated to close a stack may be as much as 2 to 3 billion gallons. The stack will also be saturated with another 4 billion gallons of what is called "pore water" that will drain from the stacks and need treatment.

Improving the quality of process water and reducing the quantity of the water that is stored has become one of FIPR's priority research tasks since Mulberry Corporation notified the Florida Department of Environmental Protection (DEP) in February 2001 that it was in financial distress and abandoning its two phosphate fertilizer plants and three phosphogypsum stacks. The phosphogypsum stacks had ponds atop them full of process water with nowhere to go since the chemical processing plants are shut down and the rainy season was approaching. In the end, the state of Florida will have paid $160 million to close the abandoned stacks.

Early on, the phosphate industry and the DEP asked FIPR to form a special advisory committee to consider short-term solutions for cleaning the water at Piney Point in Manatee County (one of the abandoned plant sites) and long-term solutions for decreasing the volume and improving the quality of the process water associated with the chemical processing of phosphate rock in all Florida operations.

DEP reached an agreement with Cargill Crop Nutrition in 2002 to manage and close the two phosphogypsum stack systems at the Mulberry plant in Polk County. The Piney Point phosphogypsum stack has been another story.

Piney Point is located about a mile from the shores of Tampa Bay and heavy rains during 2002 and 2003 have hindered efforts to drain the process water from the phosphogypsum stack. Since the plant was not operating, the pond remained full and threatened to spill into Bishops Harbor, a prized estuary. Drainage efforts at Piney Point have included double-lime treatment of the water and dispersing it 140 miles offshore into the Gulf of Mexico in accordance with an emergency permit the U.S. Environmental Protection Agency (EPA) issued in April 2003. The dispersion plan was controversial and generated a significant amount of media interest.

Mulberry's story also sparked legislative interest in what could happen to the billions of gallons of process water stored on and around the more than 20 phosphogypsum stacks in Florida. During the 2003 session a bill was passed increasing the tax the phosphate industry pays on the phosphate it mines, changing the way the tax is distributed, and defining how phosphate companies will guarantee stack closure funding.

Here is what FIPR has been doing to help find solutions:

• In 2002/2003 FIPR put much of its research on hold to commit $900,000 to demonstrate a Reverse Osmosis (RO) process that promises to be substantially more effective than the RO process currently being used at Piney Point and will leave behind a reject water stream with fewer impurities. FIPR is also looking at potential uses for the reject water and ways to remove the ammonia from it. Application of this new technology likely will double the amount of water cleaned daily.
  
  After months of negotiation, the project was put in place at the end of December 2003 and is projected to potentially produce 700,000 gallons of clean water from each 1 million gallons of pond water it processes.
  
  
• FIPR is funding a study to determine if it is feasible to use an intermediary liner system in the pond to reduce the quantity of water stored in the stack.
  
  
• FIPR is reviewing research worldwide on wastewater treatment and disposal options.
  
  
• FIPR is reviewing proposals to change process technology to reduce the quantity and improve the quality of process water that is generated.
  
  
• FIPR has funded a study to evaluate the feasibility of irrigating grass with various types of undiluted and diluted effluent water.