Recovery of phosphate from Florida beneficiation slimes I. Re-identifying the problem

Thirty phosphatic clay (slime) samples were collected from four operating plants in Florida. These samples were thoroughly characterized in order to identify feasible techniques for recovering the phosphate values. It was found that three major characterisrics of the slimes cause extreme difficuflty in recobvering the phosphate economically: the high content (30–50%) of clay minerals, the ultra-fine particle size (35–50% below 1 micron), and the nearly even distribution of phosphate among the different size fractions. Preliminary tests excluded magnetic separation and an electrical method as potential solutions. However, sizing tests using a six-inch hydrocyclone showed some encouraging results, generating an underflow product of approximately plus ten microns in size with 18% P2O5, 0.5% MgO, and 3.3.% Al2O3. Based on the detailed physicochemical analyses and some preliminary separation tests, the most viable approaches seem to be selective flocculation, sizing followed by flotation, and perhaps bioleaching.