Phosphate Mine Tailings

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Courtesy of TenCate Geosynthetics Netherlands bv

THE CHALLENGE

A typical phosphate mining operation can produce between 180,000 and 225,000 gallons per minute of fine phosphatic clay tailings. This material has a solids concentration of between 2% and 7% on a dry-solids basis. Currently, ponds and lagoons are used for settling and clarification of these materials. Many of these polishing ponds are approximately 200 to 300 acres in size, and daily maintenance is a large capital investment. The state of Florida, certain counties of Florida, and the Florida Phosphate Institute are interested in evaluating economical methods of filtration and volume-reduction that would reduce this present large land-use method.
Miratech was contacted by the institute to present information on its Geotube dewatering processes. Miratech was given a quantity of tailings for bench-scale testing.  Both Ciba and Hychem, Inc. provided the polymers.

OBJECTIVES

The objectives of the tests were to determine if this fine phosphatic clay material could be flocculated, captured, and filtered with the Geotube industrial fabric system. In addition, the other objectives were to achieve the highest cake dry solids as possible and to produce essentially clear filtrate.

TESTING

  • Samples of phosphate mining tailings are normally tested for:
  • Gradation of Solids
  • Water Content
  • Percent Solids
  • Density
  • pH

Several jar tests were conducted with various types of polymers and dosages. Numerous filter fabrics were tested in order to determine capture and filtrate quality. The phosphatic clay residue was conditioned utilizing Ciba Product No. 336 and Hychem product No. 2700.

It was decided to conduct separate tests with the Geotube GT500 polypropylene and the Geotube GT1000 polyester materials. The Geotube GT500 polypropylene material (see Table 1) is a more open woven fabric with an AOS of 40 (0.425mm). The Geotube GT 1000 polyester woven fabric has an AOS of 100 (0.150mm). Normally you would expect the fine particles of the clay to pass through a material, which has an AOS or sieve of 40. However this was not the case in our tests.

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