This study examines main and interaction effects of frother type, collector and pH on the efficiency of column flotation of Florida phosphate. Two types of frothers are used including sodium alkyl ether sulfate, as an anionic frother, and mixed polyglycols as a nonionic frother. A mixture of fatty acid and fuel oil is used as a collector. The results show that column flotation, depending on the operating conditions, can give phosphate concentrates of high grade (similar to 31% P2O5) at a recovery as high as (similar to 99%). However, interaction between frothers and the collector and consequently the flotation efficiency were found to be dependent on frother type. Specifically, anionic frother was found to lose its ability to stabilize the froth in the presence of low dosages of collector. An anionic frother used in the presence of conditioning water containing residual collector (i.e., supernatant water after conditioning solids with collector) resulted in a significant reduction in recovery. This phenomenon does not occur with the polyglycol (nonionic) frother. Flotation results of the three-phase system have been confirmed by results obtained in two-phase experiments where a low dosage of collector is added while measuring air hold-up in the presence of different frothers. The residual collector reduces air hold-up and increases bubble size when added with the alkyl ether sulfate (anionic) frother. On the other hand, a synergistic effect was obtained in the presence of the nonionic frother. (C) 2000 Elsevier Science B.V. All rights reserved.