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