Picobubble enhanced flotation of coarse phosphate particles

Froth flotation is used widely for upgrading raw phosphate which separates phosphate particles from matrix phosphate on the basis of their differences in physical and surface chemistry. However, low recovery of coarse phosphate particles has been a longstanding problem in the Florida phosphate industry which generates up to 85% of the United States phosphate rock. The flotation recovery of coarse phosphate flotation feed (-1.18 + 0.425 mm) is much lower than that achieved on the -0.425+0.15 mm size fraction even if the coarse feed is conditioned and floated separately. The tailings contain more than 20% P2O5 which is higher than the grade in the overall flotation feed. Enhanced recovery of coarse phosphate particles is of great economic and environmental importance for the industry.;In this investigation, significant recovery improvement of coarse phosphate flotation was achieved using cavitation-generated picobubbles (<1microm) in a specially designed monobubble flotation column for fundamental study, a laboratory-scale flotation column and a bank of industrial scale mechanical flotation cells. It was found from theoretical analysis and experimental observations in this study that both the low attachment probability and high detachment probability were responsible for the low flotation recovery of coarse phosphate particles.;The fundamental study of phosphate particle-bubble attachment and detachment revealed that the existence of picobubbles in flotation slurry reduced the rinsing velocity of conventional-sized flotation bubble, which increased the bubble-particle sliding time, decreased the tangential velocities of particle sliding on bubble surface, and thus increased the bubble-particle attachment probability and decreased the detachment probability. The theoretical analysis and modified monobubble Hallimond tube flotation test results have demonstrated that the flotation recovery of coarse phosphate particles can be enhanced by using a combination of small and large bubbles. Specially designed monobubble column flotation test results proved that the presence of picobubble increased the coarse phosphate flotation probability.;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 characteristic of phosphate samples. Picobubbles reduced the collector dosage by 1/3 to 1/2. Picobubbles almost doubled the coarse phosphate flotation rate constant and increased the flotation selectivity index by up to 25%.;In-plant testing with a bank of industrial flotation cells treating unsized phosphate flotation feed revealed that the use of picobubbles increased P2O5 recovery, the flotation separation efficiency and concentrate grade by about 5.6, 5.2 and 0.2 absolute percentage points, respectively. The presence of picobubble increased the coarse phosphate particle flotation recovery by 4.2, 61.2 and 88.9 absolute percentage points for the -0.60+0.425 mm, -0.85+0.60 mm and -1.18+0.85 mm size fractions, respectively.;In summary, a remarkable enhancement of coarse phosphate flotation recovery was achieved by introducing picobubbles into a specially designed monobubble flotation column, a laboratory scale flotation column and a bank of industrial scale mechanical flotation cells. The commercial testing results showed that the application of picobubble enhanced phosphate flotation was economically feasible.;KEYWORDS: Froth Flotation, Coarse Particles, Cavitation, Picobubble, Phosphate...