The use of relatively cheap composite additives to separate impurities and reduce the viscosity of concentrated iron ore slurries, if adopted for similar types of iron ores to those tested, might upgrade the quality of iron ore, and reduce water use and the size of tailings dams. These composite additives based on NaOH and phosphate-based chemicals, reduced the viscosity and yield stress of these slurries by more than 90%. It separates the impurities particularly clay minerals from iron oxide particles by electric double layer repulsion enhancing the beneficiation performance. The ease of significant yield stress enhancement of dispersed concentrated tailings by the addition of low cost lime was demonstrated. High yield stress tailings are much less dangerous in the event of a dam wall failure due to slow flow and continually increasing yield stress as they gather more soil material along their flow path. In this paper we suggest how composite additives of NaOH and phosphate-based chemicals can be used to effectively reduce the viscosity and enhance impurity separation meeting all the environmental requirements in terms of pH and chemical leachate. CITATION:Leong, Y K, Drewett, J and Bensley, S, 2019. Reducing the viscosity of concentrated iron ore slurries with composite additives for quality upgrade, reduced power, safer tailings storage and smaller environmental footprint, in Proceedings Iron Ore 2019, pp 738743 (The Australasian Institute of Mining and Metallurgy: Melbourne).