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Field Evaluation of Sand-Clay Mix Reclamation


The subject project involved field monitoring of the partial filling of Reclamation Area R-2 with sand-clay mix at CF Mining Corporation’s Hardee Phosphate Complex, Hardee County Florida. Figure 1.1 shows the general location of the reclamation area, which covers approximately 110 acres. The area was previously mined and is surrounded by earthen dikes with an average height of 25 feet above grade and a crest elevation of 135 feet (MSL). At the maximum design fluid elevation of 130 feet (MSL) the mix will average about 35 feet deep. In some of the isolated deep pits which were left in the bottom of the reclamation area, the depth will approach 50 feet when filled to the maximum design fluid level. The reclamation area has a total storage capacity of approximately 3600 acre-feet at maximum design fluid level and is constructed with a divider dike located approximately halfway between the east and west walls. The layout of the reclamation area is shown in Figure 1.2.

The sand-clay mix reclamation method utilized by CF is briefly discussed as follows. Waste phosphatic clays from the beneficiation plant enter Initial Settling Area N-l where they are allowed to thicken through the process of natural settling and consolidation to a solids content in the range of 12% to 18%. A dredge is then used to excavate the thickened clay and pump it to a mixing station where it is mixed with sand tailings. The sand tailings are pumped from the flotation plant to the mixing tank where they are dewatered by cyclone prior to mixing with the clay. After the dewatered sand tailings and thickened clays are mixed they are pumped to the reclamation area where they are used to fill the previously mined-out cut. Water is decanted from the surface of the sand-clay mix as the reclamation area is filled and the sand clay mix consolidates. After consolidation, the land is revegetated and reclaimed.