Phosphorus mining has a beneficial side and a disturbing side. It gives us ammonium phosphate, a key ingredient in the fertilizer used to grow abundant food. It also produces massive amounts of waste, depicted here.
The phosphorus comes from calcium phosphate rock that is strip-mined across several U.S. states and pulverized. Producers add sulfuric acid to form phosphoric acid, which is later converted to ammonium phosphate. Every ton of phosphoric acid generated creates five tons of a soil-like by-product, phosphogypsum. The white or gray substance emits radon gas and is therefore used in only a few applications, such as peanut farming. Most of the phosphogypsum is bulldozed for permanent storage into giant stacks that can reach 200 feet high and cover 400 acres or more. A gypstack contains one billion to three billion gallons of wastewater that gradually diffuses out, creating small lakes that shimmer blue or green as light bounces off bottom sediment. The water’s pH is between 1 and 2, corrosively acidic. The photograph shows the corner of one such stack in Florida and the lake beside it.
Florida generates 75 percent of the phosphorus that U.S. farmers use and about 20 percent of global supply. More than one billion tons of phosphogypsum lie piled in 25 stacks across the state; 28 million tons get added every year.