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Pilot-Scale Testing and Demonstration of Picobubble-Enhanced Flotation of Phosphate for Increased Recovery and Reduced Reagent Consumption



The United States is the largest phosphate rock producer in the world. 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 -106µm (-150 mesh) phosphate portion contains virtually all of the clay minerals and is discarded as slimes due to lack of cost-effective beneficiation processes. The intermediate -1.18 mm +106µm (-16 +150 mesh) portion is a mixture of quartz and phosphate minerals. Beneficiation of this size fraction is often accomplished using the “Crago” two-stage froth flotation process. The flotation recovery of coarse flotation feed (-16 +35 mesh) is often below 60%.

In this investigation, significant recovery improvement of coarse phosphate flotation was achieved with laboratory- and pilot-scale flotation columns. The laboratory-scale flotation column tests showed that picobubbles increased P2O5 recovery by up to 23%~30% for a given acid-insoluble (A.I.) rejection, depending on the characteristics of the phosphate samples. Picobubbles reduced the collector dosage by ⅓ to ½. Picobubbles almost doubled the coarse phosphate flotation rate constant and increased the flotation selectivity index by up to 25%. The pilot-scale picobubble-enhanced flotation tests with the unsized plant feed indicated that the use of picobubbles increased P2O5 recovery and flotation separation efficiency by up to about 5 absolute percentage points. A size-by-size analysis of flotation products revealed that the presence of picobubbles at a high flow ratio improved the flotation efficiency by 4.4% and 8.7% for the phosphate particles of 0.6 mm and 0.8 mm, respectively. It was found from fundamental studies using cavitation-generated picobubbles (<1µm) in a specially designed monobubble flotation column that both the low attachment probability and high detachment probability were responsible for the low flotation recovery of coarse phosphate particles.