degree of separation required and other variables in one preferred form of the invention a cyclone type centrifugal separator is used within the centrifugal separator 4 the feed liquid is split between the overflow line 10 and the underflow line 11 the split between these lines 10 and 11 can be controlled as appropriate by varying several operating parameters of the centrifugal separator 4 including the diameter of the separator the separator length the angle of the separator barrel the size of the inlet underflow and internal nozzles the feed pressure and the feed density in testing it has been found somewhat surprisingly that with a partially aerated feed liquid and approximately tuned operating parameters a relatively small overflow stream can be produced which contains the vast majority of the froth leaving a proportionately large volume of de aerated underflow liquid having a density similar to that of the feed liquid in the preferred embodiment of the invention the underflow 11 feeds the de aerated liquid from the centrifugal separator 4 to a thickener not shown this obviates the problem of accumulation of excess from in the thickener and the associated feedwell which in prior art devices significantly reduces the efficiency of the thickening process the froth stream from the centrifugal separator overflow line 10 is fed to a launder 15 and broken down with fine water spray jets 16 this produces a third components consisting of liquid from the spray jets 16 mixed with the liquid from the collapsed froth which may be.