Abstract

Mineral industries in common generate a lot of rejects in the form of fines and slimes, which ultimately create environmental and social problems besides causing losses of mineral values. In view of the recent stringent policy imposed on the environment, there is an urgent need to attempt possible simple and cheap solutions to such problems. These slimes have long been considered in the industry to be unrecoverable. It has been standard practice over many years in the phosphate industry to separate and discard the fines and ultrafine particles.

In this respect, the present study shed light on the recovery of super and ultrafine phosphate of a phosphomud produced after the processing of an East Mediterranean phosphate ore. Falcon Concentrator model SB40-VFD (semi-continuous with variable frequency drive) was used in this study to recover the -32 micron phosphate fines of D50=11 micron. The effect of the main variables of the semi-continuous Falcon concentrator model SB40-VFD, including the bowl rotation frequency Hz, the fluidizing water pressure psi, and feeding rate g/min on the separation efficiency were followed up. In addition, two feeding modes based on a particle size-by-size were tried in this study: The sample was fed as a global -32 micron sample or as two fractions, -32+11 micron, and -11 micron samples. Central Composite Rotatable Design (CCRD) was applied on the Falcon separation of the -11 micron fraction with D50 < 3 micron alone to model and optimize the separation process for the two responses: the recovered phosphate grade and recovery.

Results showed that the phosphate fines containing 14.73% P₂O₅, 15.03% acid insoluble, and 19.07% loss in ignition was recovered with grade and P₂O₅ recovery reaching 28.29%, and 95.97% in case of separating the overall -32 micron sample as one feed. In case of the fractionated feeding samples, the total grade and recovery reached 29.21%, and 88.42%, respectively. The application of the CCRD results showed that the bowl rotation frequency showed to have the main irreversible effect on the product grade, where the fluidizing water pressure had the main reversible effect on the recovery. On the other hand, feeding rate showed some effect on the product grade with almost no effect on its P₂O₅ recovery%.

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