New Technology for Disaggregation and Slurrying of Florida Phosphate Matrix

Phosphate mining represents a significant industry in the State of Florida. In view of the great demand for resources, the industry is in a strong public focus. In mining and processing, the phosphate ore mining process alone is responsible for about 45% of the total energy consumption. Slurry pumping to the processing plant accounts for one third of the energy consumption during mining. Various studies have shown that the optimum solid-water ratio for slurry pumping is approximately 60 wt%. It is difficult to achieve this value with the technology of hydraulic monitor operations applied at the present time. For operational reasons, more precise control of the solids content is almost impossible. The Florida Industrial and Phosphate Research Institute therefore funded this research project.Disaggregation and slurrying of phosphate matrix represents the principle problem in pumping slurry. It is still state of the art to use draglines in phosphate ore mining. The dragline dumps the phosphate matrix in the pit, where it is slurried with the help of hydraulic monitors and conveyed to a static grizzly. The grizzly is used to scalp larger rocks and roots. It requires cleaning at regular intervals. A suction pump situated behind the grizzly, pumps the slurry to the processing plant. The average solids content of the slurry is only about 25-35wt%, and varies widely depending on the material properties.Under this investigation, four different types of phosphate ore were examined. In the first step the phosphate ores were analyzed and characterized. Then two different methods were evaluated to improve the slurrying process. First, tests were performed using high pressure water jets of up to 200 bars in order to disaggregate the phosphate matrix. In principle, it is possible to achieve disaggregation and slurrying using this technology, but the necessary throughput cannot be acquired due to the long retention time required. Second, selective crushing tests were carried out using a wet hammer mill. This technology was able to achieve a solids content of 60 wt%, while still producing a high degree of disaggregation of the clay agglomerates, without destroying the valuable material. A preliminary design for a mobile disaggregation and slurrying unit was developed on the basis of these test results. The new technology could reduce water demand from 2.16 m3/t to only 0.58 m3/t and energy consumption from 1.32 kWh/t to 0.36 kWh/t.