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Development of Picobubble Flotation for Enhanced Revovery of Coarse Phosphate Particles



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 pebble with no further upgrading required, but the beneficiation of the -1.18mm (-16 mesh) fraction is needed. Froth flotation is the most widely used process for Florida phosphate beneficiation. However, flotation recovery of the coarse (16 + 35 mesh) phosphate is low (<80%), while the fine (-150 mesh or -106 microns) portion that contains virtually all of the clay minerals is discarded in the hydrocyclone overflow. The low flotation recovery of coarse particles is mainly due to the high probability of detachment of particles from the bubble surface.

The proposed project was aimed at developing practical and effective techniques for enhanced recovery of coarse phosphate particles. A specially designed flotation column that utilizes picobubbles (bubbles with a size under 1 ┬Ám that are characterized by high collision probability, low detachment probability, low ascending rate, and high free surface energy) was developed to achieve the goal. Cavitation-generated picobubbles are characterized by an inherently high probability of collision, a high probability of attachment and a low probability of detachment, and therefore are very effective for enhancing flotation recovery of fine and coarse phosphate particles. Other major advantages of the developed 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.

The test results of two CF Industries phosphate samples and one Mosaic phosphate sample indicate that the P2O5 recovery can be increased by up to ~23%-30%, depending on the characteristics of the phosphate samples. With picobubbles, collector dosage can be reduced by 1/3 or 1/2. The centrifugal force created by the specially designed column bottom further improves the separation performance.