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The Bone Valley is a region of central Florida, encompassing portions of present-day Hardee, Hillsborough, Manatee, and Polk counties, in which phosphate is mined for use in the production of agricultural fertilizer. Florida currently contains the largest known deposits of phosphate in the United States. ==Process== Large walking draglines, operating twenty-four hours a day in surface mines, excavate raw pebble phosphate mixed with clay and sand (known as matrix). The matrix contains a number of chemical impurities, including naturally occurring uranium at concentrations of approximately 100 ppm. Because this phosphogypsum is slightly radioactive, its use is banned in most situations.〔()〕 The matrix is then dropped into a pit where it is mixed with water to create a slurry, which is then pumped through miles of large steel pipes to washing plants. These plants crush, sift, and separate the phosphate from the sand, clay, and other materials, and mix in more water to create a granular rock termed wetrock. The wetrock, which is typically of little use in raw form, is then moved largely by rail to fertilizer plants where it is processed. The final products include, but are not limited to, diammonium phosphate (DAP), monoammonium phosphate (MAP) and triple superphosphate (TSP). Waste byproducts are stored in large phosphogypsum stacks and settling ponds, often hundreds of acres in size, and up to tall. Phosphate processing produces significant amounts of fluorine gas, which must be treated by filtering through special scrubbers. Much of the final product (known within the industry as 'dryrock') is transported by rail to facilities along Tampa Bay, where they are transloaded onto ships destined for countries such as China. Phosphate product intended for domestic use is assembled into long trains of covered hopper cars for northbound movement. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bone Valley」の詳細全文を読む スポンサード リンク
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