Development of Innovative Processes for Enhanced Recovery of Coarse and Fine Phosphate

The Florida phosphate industry generates up to 85% of the United States phosphate rock. In a typical central Florida phosphate beneficiation plant the phosphate ore is washed and classified into three major size fractions. The coarse +1.18 mm (+16 mesh) portion is primarily phosphate pebbles and no further upgrading is needed. The fine -106 ~lm phosphate (-150 mesh) portion contains virtually all of the clay minerals and is discarded as the slimes. The lost phosphate in the phosphatic clay accounts for 20% to one third of the matrix phosphate value. The intermediate -1 rom + 106 /lm (-16 +150 mesh) portion is a mixture of quartz and phosphate minerals. Beneficiation of this size fraction is often accomplished using the "Craigo" two-stage froth flotation process. It is well known that flotation recovery of coars~ flotation feed (-16 + 35 mesh) is often below 60%. The combined loss of phosphate in flotation tailings and fine phosphate slimes usually amounts to about 40% of the original phosphate value. The particle-bubble collision, attachment and detachment are the most critical steps in the flotation process. The low flotation recovery of fine particles is mainly due to the low probability of bubble-particle collision while the main reason for poor flotation recovery of coarse particles is the high probability of detachment of particles from bubble surface.. Fundamental analysis indicated that use of smaller bubbles is the most effective approach to increase the probability of collision and reduce the probability of detachment. The main goal of the proposed project is to develop practical and effective techniques for enhanced recovery of coarse phosphate particles. A specially designed column that integrates centrifugal gravity separation and picobubble column flotation will be developed to achieve the goal. Picobubbles will be produced using the hydrodynamic cavitation principle. They are selectively attached onto the hydrophobic particles, reducing the effective density of the bubble particle aggregate and enhancing the centrifugal gravity separation. Cavitation generated picobubbles are characterized by inherently high probability of collision and high probability of attachment and low probability of detachment due to their tiny size, and therefore are very effective for enhancing flotation recovery of fine and coarse phosphate particles. Other major advantages of the proposed technique include much lower collector dosage and air consumption since picobubbles are produced from air naturally dissolved in water and they act as the secondary collector on particle surface, resulting in considerably reduced operating cost.