River. Mining of these deposits was by hand labor and production was low 

 (Canterbury 1978). By 1888, however, production shifted from river deposits 

 to land-pebble deposits discovered in Bone Valley, about 25 miles east of 

 Tampa. Production was 2,700 metric tons in 1888, 275,500 metric tons in 1892, 

 680,000 metric tons in 1900, 3.3 million metric tons in 1930, and 36 million 

 metric tons in 1975 (Hoppe 1976; Canterbury 1978). 



As the demand for fertilizer grew and technology advanced, the volume and 

 efficiency of recovery increased. Nevertheless, the phosphate industry in 

 Florida is characterized by a small number of producers because of the large 

 capital investment required to mine phosphate (Canterbury 1978). The ten 

 major phosphate companies in Florida produced 80% of the U.S. total in the 

 1950's and 85% in the 1960's. In the 1970's, 15 companies mined over 95% of 

 the nation's phosphate rock (Canterbury 1978). 



PHOSPHATE PRODUCTION 



Three Southwest Florida counties fall within the 5-county Central Florida 

 Phosphate District, an area of approximately 5,180 km (2,000 mi^) (U.S. Envi- 

 ronmental Protection Agency 1978). This area, sometimes referred to as the 

 Pebble Phosphate District, or Bone Valley, is one of the world's largest 

 sources of phosphorite or amorphous phosphate rock (Figure 3). 



The rock occurs in sedimentary deposits of marine origin. Chemical 

 analysis of phosphate rock are reported as percent phosphorous pentoxide 

 (P2O5), tricalcium phosphate (CA3PO4), or bone phosphate of lime (BPL). One 

 percent BPL is equivalent to 0.46 P2O5. Fertilizers manufactured from triple 

 superphosphate and diammonium phosphate have about 46% P2O5 (Wilbur Smith and 

 Associates 1980). 



The production of the Bone Valley phosphate industry in Florida in 1976 

 accounts for about 80% of U.S. production and 33% of the world production. In 

 Southwest Florida, Hillsborough, Manatee, and DeSoto Counties produce the most 

 phosphorous. The principal activities associated with the phosphate industry 

 are mining, beneficiation, chemical and nonchemical processing, and mineral 

 transportation. The standard mining practice in the Florida land-pebble phos- 

 phate fields is to remove the overburden and mine the phosphate matrix with 

 electric powdered drag lines (U.S. Environmental Protection Agency 1978). 



The overburden is typically quartz, sand, and clay averaging 6 m (20 ft) 

 in thickness. In a typical 1-year operation, 162 ha (400 acres) of land are 

 mined and 9.9 million m-^ (13 million yd-^) of overburden and 6.9 million m^ (9 

 million yd3) of matrix are removed. In the Bone Valley area in 1976, about 

 2,000 ha (4,940 acres) were mined (U.S. Environmental Protection Agency 1978). 

 The phosphate industry currently owns either the land or mineral rights to 

 areas with enough phosphate deposits to continue the present rate of produc- 

 tion beyond the year 2000 (U.S. Environmental Protection Agency 1978). 



After the area is mined, land reclamation for strip-mine areas begins to 

 show effects within 2 to 3 years, but the reclamation of slime-holding ponds, 

 an integral part of the phosphate strip-mining process, may take as long as 10 

 years. In 1979, the following companies engaged in phosphate mining in South- 

 west Florida: International Minerals and Chemicals Corp. (IMC); Brewster 



132 



