Glass, poly(vinyl chloride), polyethylene and/or polypropylene beads were suspended in water by mech. stirring under lab. conditions to select the most efficient construction of mixers and shape of mixing blades in the case when both light and heavy beads were suspended. The optimum geometry showed a 2-turbine agitator with inclined blades which allowed for simultaneous down and up motion of suspensions (energy consumption below 200 W/m(3)).