Phosphogypsum stack

• Large aboveground piles (up to 200 feet high) of by-product phosphogypsum located near phosphoric acid plants. The gypsum slurry is pumped to the top of the stack where it settles out and the slurry water returns to the plant as part of the system to cool process water. As the stack fills with deposited gypsum, the solids are scooped out to build up the sides, and the stack grows in height as the process is repeated. Since there is a required slope to the sides, a point is reached where no further material can economically be placed on the top, and the stack is then closed.

Source: FIPR