Abstract
The effect of EDTA on the total cyanide distillation (JIS K 0102 38) has been studied. Cyanide ion could be recovered quantitatively by distillation from most of the cyanide compounds without EDTA. However some compounds, e.g., potassium hexacyanocobaltate (III), did not give good cyanide ion recovery either with or without EDTA. For ferri (ferro) cyanide in the presence of a large excess of some metal ions, EDTA was effective for the quantitative distillation of cyanide. It could therefore be presumed that EDTA prevented the formation of insoluble ferri (ferro) cyanide by the chelate formation with the metal ions added and did not dissociate the ferri (ferro) cyanide ion. The reagents used in Standard Methods (APHA) showed almost the same effects on the cyanide distillation as those given by the reagents used in the JIS method. For some actual waste waters, the JIS method (EDTA involved) gave the higher analytical values of cyanide than Standard Methods (EDTA not involved). This suggested the participation of EDTA in the formation reaction of cyanide ion.
