Fine coal froth flotation: Particle size experimental behavior and modeling

In response to documented need for ultrafine coal flotation data in order to map recovery functions this work investigated the behavior of particle size in conventional froth flotation of fine and ultrafine coal. Pilot plant and bench scale continuous flotation experiments varied particle size (5 to 150 ;Ultrafine coal particles floated much better than equivalent sized ash and pyrite while increasing aeration favored the recovery of finer particles. The interpretative framework chosen utilized FLOTE, a phenomenological, steady state, distributed rate constant, kinetic flotation model. FLOTE allows elaborate schemes for solids description but can be demanding in data and was found to greatly underpredict the recovery of ultrafine particles. Alternate particle-bubble capture efficiency functions were considered encompassing particle-bubble collision, attachment and detachment. The regressed bench test FLOTE parameters captured froth variation by estimating greater differences in the relative floatability of coal and ash for taller froths. The froth solids transmission coefficients were found to represent the deviation of the chemical conditions in an individual cell from average flotation plant values. Estimating these coefficients directly from the data significantly improved overall model performance and showed that the individual cell values may be linearly related. Turbulent intensity parameters acted as shape factors for the particle-bubble capture function used to predict size recoveries. The maximum floatable size was overpredicted by the suggested calibration method based on lognormal particle size distributions. All tested particle-bubble collision models overpredicted the recovery of the coarsest particles unless the average particle size of the coarsest class was fixed at values very close to the maximum particle size. On the other hand, recovery of the ultrafine sizes was underpredicted indicating that significant particle flocculation or alternative capture mechanisms may be operating in the ultrafine range.