In this study, reverse flotation was applied to recover phosphate from a very low grade (5.01% of P(2)O(5)) sedimentary ore. Sodium silicate, starch, tannic acid, aluminum sulfate, (Na,K)Tartarat, sodium tripolyphosphate, H(3)PO(4), and H(2)SO(4) were used as phosphate mineral depressants in acidic and alkaline conditions. Oleic acid and Armac-T were added as carbonate and silicate collectors respectively, while pine oil was used as a frother and fuel oil as modifier. It was demonstrated that aluminum sulfate and (Na,K) Tartarat work synergistically to depress phosphate minerals. An experimental protocol was devised to optimize the grade and recovery of phosphate using two different methods: anionic-cationic and cationic-anionic. Anionic-cationic method was found more effective. (C) 2011 Elsevier B.V. All rights reserved.