Abstract: Aggregate-forming suspensions containing a coagulant therefor, e.g., FeCl.sub.3, polyaluminum chloride or Al.sub.2 (SO.sub.4).sub.3, are coagulated/flocculated by stirring to provide mechanically strong flocs of greater average diameter size, without concomitant formation of irreversible microflocs, and wherein the stirring regime, in at least the initial stage of coagulation/flocculation, includes an initial operating stirring cycle comprising (i) a rapid stirring sequence at an average velocity gradient ranging from 300 to 1,000 s.sup.-1 for a period of time ranging from 30 to 200 seconds, and (ii) a slow stirring sequence at an average velocity gradient ranging from 40 to 100 s.sup.-1 for a period of time ranging from 5 to 40 minutes.