The role of sodium silicate as depressant/dispersant on siliceous phosphate flotation was empirically evaluated. Factorial experimental design was used to investigate the effect of sodium silicate and its interactions with collector dosage and feed characteristics on phosphate recovery and silica depression. Analysis of variance (ANOVA) conducted on flotation results of unslimed feed showed the existence of synergistic effects between collector, sodium silicate and feed characteristics (P80) which emphasise the necessity to design a reagent suite for each specific feed characteristic. (C) 2009 Elsevier B.V. All rights reserved.