Reverse flotation is a commonly used technique for separating carbonate impurities from sedimentary phosphate ores using fatty acids collectors. Although, oleic acid represents one of the famous fatty acids that have been used as a collector in phosphate flotation circuits, it is a non-selective collector. Therefore, the selection of depressing agent is the most controlling factor. In this study, sodium sulphate was used as a phosphate depressant. The role of sodium sulphate in separating phosphate from its impurities and producing an acceptable concentrate grade for phosphoric acid production (equals or more than 30% P2O5) was evaluated using augmented factorial design. The collector dose, depressant dose, solid %, flotation time and pH were chosen as main affecting variables. The results showed that the addition of sodium sulphate improves the phosphate grade and recovery especially at highly acidic pH. They showed also that the solid % and the pH represent additional key factors in achieving a good grade concentrate due to their role in controlling the amount of ionic species in the flotation pulp. A concentrate contains >32% P2O5 was obtained with a recovery ranges from 84% to 87%. (C) 2014 Elsevier B.V. All rights reserved.