 The synergies between foam fractionation and froth flotation have been explored in a 2009 special issue of the Asia Pacific Journal of Chemical Engineering.Robert Lemlich showed how foam fractionation columns can be operated in stripping, enriching, or combined modes (depending on whether the feed is sent to the top, bottom or middle of the column), and can be operated with or without an external reflux stream at the top of the column.It helps to think of the process as similar to a gas-liquid absorption column.