SBM uses separate beneficiation methods for different size fractions of ore. While beneficiation methods (except the patented heavy media separation plant) are similar to those used at other phosphate operations, the degree to which the specific methods are tailored to material size is unique to Four Corners. Beneficiation occurs in three separate plants: (1) the washing plant, (2) the heavy media separation plant, and (3) the flotation plant. Operations in each of these plants are discussed in the following sections
The washer plant provides for size separation of the matrix ore into clays, fine product, dolomite product, and oversized debris. A flow diagram for the washing plant is presented in Figure 5. In the washing plant, there are two washer circuits (the North and South washers). Each circuit can receive matrix ore from two of IMC's four draglines. The two draglines that feed a washer circuit alternate between mining matrix ore and removing topsoil and overburden such that the circuit is only receiving ore from one dragline at any given time.
In the heavy media separation plant, an unspecified volume of water is initially added to the dolomite product, which is then passed through two stages of hydraulic screening. The dolomite product is separated into: (1) greater than 5 mesh material, which is classified as waste , (2) less than 5 mesh to greater than 16 mesh material, which goes to heavy media separation, and (3) residual less than 16 mesh material, which goes to the flotation plant. The wastewater from the screening stages is recycled within the plant.
The less than 16 mesh material from the washer plant is pumped to two "unsized" feed bins (100-foot diameter and 45-foot height). These bins feed the flotation plant, where the material is initially separated into three size fractions; fine, coarse, and spiral. In the first separation stage, "fine" material (less than 35 to greater than 150 mesh) is hydraulically separated (by density). The remaining material (less than 16 and greater than 35 mesh) is then passed over Derrick screens to separate the "spiral" (less than 16 and greater than 24 mesh) and "coarse" (less than 24 and greater than 35 mesh) fractions.