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

02-172-240Final

Abstract

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.