Removal of Ferricyanide and Ferrocyanide Ions from Waste Water by Means of Ion Flotation Technique

Abstract

Some experimental results are presented in which ferricyanide and ferrocyanide ions (initial concentration being 5.3 ppm) were removed from their aqueous solutions by means of ion flotation technique. Ferricyanide ion can form a sparingly soluble and hydrophobic precipitate by the addition of cetyltrimethylammonium bromide (CTMAB), thereby ferricyanide ion can be removed as a scum in a column separator or Denver type flotator. The latter required less flotation time than the former. Solubility products of the precipitates, of ferricyanide-CTMA, the composition of which being {Fe (CN), } (CTMA)3, was determined to be 4.3 x 10-22.The most successful result was obtained under the condition that the molar ratio of ferricyanide ion to CTMAB was from 1.0 to 1.5 and the range of pH of solutions was from 5 to 8. In the above condition, the residual concentration of ferricyanide ion was found to be less than 0.5 ppm. Equally successful results were obtained with the solution containing ferrocyanide ion. Ion flotation of ferricyanide ion by CTMAB was not appreciably influenced by the presence of sulfate ion up to the sulfate concentration of 1000 ppm.In the case of ion flotation of ferricyanide ion where dodecylbenzyltrimethylammonium chloride (DBTMAC) was used as a collector, no successful removal of ferricyanide ion was achieved by the use of Denver type flotator. This may be interpreted in terms of the higher solubility of the precipitate (solubility products 6.5x 10-12) of ferricyanide-DBTMAC; no scum was formed in the above system. However, in the case where DBTMAC was used as a collector, satisfactory results were obtained by making use of the column separator. The present results seem to indicate that Denver type flotator is preferable to the case where ions to be removed can form a scum, whereas column separator is suitable for the case where no scum is formed.