Negatively charged ions can be separated successfully by foam fractionation. Among them, free cyanide ions were removed by cetyl trimethyl ammonium bromide or a similar compound. At low concentrations (<5 mg/L), quantitative removal of free cyanide ions was observed. Further observations revealed that when the concentration was increased to 57 mg/L, a reduction in concentration equivalent to 47% could be achieved. Finally, a correlation between cyanide separation and surfactant concentration was found.