Foam Fractionation of Orthophosphate with a Cationic Surfactant

An experimental investigation is presented of the foam fractionation of orthophosphate from aqueous solution using a cationic surface-active agent, ethylhexadecyldimethylammonium bromide. The effects of initial concentration of phosphate, of initial concentration of surfactant, of pH, and of the presence of competing anions are established. Initial concentrations of phosphate range from 12.5 to 150 mg/liter (as PO₄), initial concentrations of surfactant range from 50 to 600 mg/liter, and the pH is varied from 5.0 to 13.4. Results are discussed in terms of the residual concentration of phosphate, the collapsed foam volume, the phosphate removal ratio, and the “relative fractionation” of the phosphate and surfactant into the surface layers of the foam-producing bubbles. Optimum results are achieved between pH 8 and 9 and in the total absence of competing divalent anions. The removal of 99 per cent of 9.0 mg/liter phosphate can be accomplished with 100 mg/liter of surfactant; the removal of 99 per cent of 24.2 mg/liter phosphate can be accomplished with 600 nig/liter of surfactant. Results are compared with previous work on the foam fractionation of phenolate.