Phosphoric Esters as Carbonate Collectors in the Flotation of Sedimentary Phosphate Ores

Ethoxylated phosphoric ester surfactants were evaluated as collectors for flotation of carbonates from sedimentary phosphate ores, at slightly acidic pulp pH, using sulfuric acid or sodium fluorosilicate as a phosphate depressant. With 12 to 15 carbon atoms in the hydrophobic chain, maximum collecting power was observed for 9 to 10 ethylene oxide units. Only fine carbonates, ranging in size from about 20 to 160 µm or 40 to 200 µm, were effectively removed with phosphoric ester collectors. Utilization of seawater, or water of extremely high hardness, did not detrimentally affect selectivity. Silica, silicates, and residual fine carbonates can be separated in a second flotation stage, with primary amine as a collector. Coarse carbonates are separated by direct flotation of phosphate with fluoride ion as a phosphate activator and primary amine as a collector. In a seawater pulp, fluoride ion was not required. Typical examples of laboratory and pilot- scale test results are given to illustrate capabilities of the various flotation flowsheets.