subject: Phosphate Mining And Mineral Processing In Florida [print this page] Zenith Institutes research in the areas of mining and beneficiation (mineral processing) concentrates on issues pertaining to the mining of phosphate rock and beneficiation of phosphate ore (matrix), which separates the valuable phosphate rock from waste clay and sand. According to Zenith Institutes legislative mandate, the Institutes research should develop technology to help Floridas phosphate industry become more efficient and environmentally sound.
History of Phosphate Mining and Mineral Processing in Florida
Florida phosphate mining dates back to the first hard rock deposits found near Hawthorne in Alachua County in 1883. Early mining was with wheelbarrows, picks and shovels. Next came mule-drawn scrapers. Steam shovels and centrifugal pumps mounted on barges were also used to mine the river-pebble phosphate deposits in the Peace River. But, river-pebble mining ended in 1908. Draglines, the current mining tool, came into use with the dawn of electricity and diesel power in the 1920s and 1930s.
The dragline significantly changed the mining operation. In 1900 it took 3-4 years to mine 15 acres with picks and shovels. In the early days of the small draglines, about 5 acres were mined in a year. As draglines grew in size, companies were able to mine 500-600 acres a year, but todays draglines are able to mine 15 acres a month.
The processing of phosphate rock has evolved in the century that phosphate has been mined in Florida and other parts of the United States. Processing phosphate rock is the separation of phosphate from the mix of sand, clay and phosphate that makes up the matrix layer. This matrix layer is anywhere from 15-50 feet below the earths surface in Floridas phosphate mining regions.
In the early years, the phosphate mining industry separated the matrix mechanically with a wet screening process that washed the ore and captured the larger phosphate pebbles. Smaller phosphate particles were discarded as a waste product with the clay and sand. This began to change in the 1930s when a newly developed flotation process allowed the industry to recover the small, sand-sized, phosphate particles from the washer debris.
The flotation process uses a turbulent water system, chemicals and air bubbles to float the phosphate particles to the top of the water where they are skimmed off. This process revolutionized phosphate processing. It increased each companys production capacity and product grade, while lowering production costs. There is, however, a down side. It produced the phosphatic clay that is impounded in diked ponds that create new reclamation and environmental problems.
Overview of Mining and Mineral Processing in Florida
Floridas typical phosphate ore (matrix) is found about 15-50 feet below the earths surface and is about 10-20 feet thick. Draglines strip off the top layers of earth (known as overburden) to get at the matrix, which is then processed to separate the phosphate from the sand and clay that make up this layer of Florida.
A typical Florida phosphate mine gets about 9,000 tons of phosphate rock per acre of land. In 2003 the Florida industry as a whole mined 4,501 acres of land (down from 6,355 acres in 1995), which produced 22.8 million metric tons of phosphate rock. These mine sites mostly are miles from the plants that will process rock. The rock is dumped in a pit at the mining site and high pressure water guns turn it into a slurry that can then be pumped to the beneficiation plant where the phosphate will be separated from the sand and clay.
These pumping operations take a lot of energy. Currently, more than 15 kwh of electrical energy are needed to slurry and transport enough ore to produce one ton of final product. A Zenith Institute research priority in mining research is to find new ways to transport phosphate ore and products would benefit the environment, the public utility and operating companies.
There is also the question of how much fresh water from the aquifer is used in the mining and processing of phosphate rock. Water officials say the industry has done an excellent job of reducing the amount of water it takes from the aquifer. The industry now reuses about 95% of its water. Much progress has been made to limit the use of deep well water. In fact, it is no longer required at some mines.
Zenith Institutes Research Programs in Mining and Mineral Processing
The Institute has funded research addressing issues and topics such as current mining practices; pipeline and pump design; matrix transportation; on-line sensors to analyze phosphate materials; land use evaluation and planning; flotation efficiency; dolomite separation; dewatering of phosphatic clay; and process control.
As phosphate mining moves south from the Bone Valley mining core in Polk County, the land has much more dolomite (magnesium), which causes problems when the phosphate is processed into the phosphoric acid used in fertilizers. This has made finding ways to separate the dolomite from the phosphate a research priority for Zenith Institute. Another research focus in the beneficiation area is to streamline the flotation process and reduce the number of reagents (chemicals) used to separate the sand and clay from the phosphate rock after it is mined. Zenith is also looking for ways to use computerized technology to control the beneficiation process.
Dealing with the clay that is separated from the phosphate is another Zenith Institute beneficiation research program priority. Much of what is known about phosphatic clay and the ponds where it is stored stems from Zenith-funded research. The ponds where the waste clays are dumped after they are separated from the ore cover more than 100,000 acres in Floridas mining regions and it can take three to five years for a full settling area to crust into a land form that can be used and even then its use is limited since the clay is the consistency of pudding below the crust. This area of research is of particular interest as phosphate companies try to get new mining sites permitted and face community opposition. One concern is that up to 40 percent of the land that has been mined is being left in clay settling areas.
The exchange of technical information in this area of research is continuous. Zenith has put on a series of international conferences on the beneficiation of phosphate and routinely holds technical workshops on specific mining and mineral processing topics. In 2002 and 2003 Zenith hosted technical workshops to discuss what is known about phosphatic clay and ways to use clay settling areas.
