The effect of Fe and Mn contents on precipitation and sedimentation of primary alpha-Al(FeMn) Si phase in liquid Al-11.5Si-0.4Mg (wt%) alloy has been investigated at 600degreesC in convection-free conditions. Almost all primary alpha-Al( FeMn) Si particles and some oxide films seem to completely settle to the base of the melts. With the increase of original iron equivalent values (IEV) or Mn/Fe ratio at a given Fe level there are increases in particle weight, number and size. The particle volume fraction and depth of sediment also increase with IEV or Mn/Fe ratio at a given iron level. However, the particle volume fraction and average sizes probably remain plateaus with IEVs from 2 to 5.5. There is an equilibrium Mn content corresponding to a precipitation temperature for a given alloy. In Al-11.5Si-0.4Mg alloy containing 0.7 - 1.22Fe and 0.3 - 2.15Mn, Mn is approximately 0.3% after sedimentation at 600degreesC. The removal efficiency of Fe and Mn increases with original IEV or Mn/Fe ratio at a given Fe level. Mn has higher removal efficiency than Fe. Experimental results for primary particle amounts and compositions were compared to predictions from software JMatPro. Good agreement was found suggesting that the modelling route could be used to explore different alloys where sedimentation would take place. (C) 2004 Kluwer Academic Publishers.