Removal of Cyanide in Ni(II)�CCyanide, Ni(II)�CCyanide�CEDTA, and Electroplating Rinse Wastewater by Ferrate(VI)

Cyanide is found as free cyanide and metal?Ccyanide complexes in metal finishing rinse wastewaters. Experiments were performed to seek removal of cyanide in Ni(II)?Ccyanide and Ni(II)?Ccyanide?Cethylenediaminetetraacetate (EDTA) solutions by the environmentally friendly oxidant, ferrate(VI) (FeO ₄ ^2? , Fe(VI)) as a function of pH (8.0?C11.0). Incomplete removal of cyanide in Ni(II)?Ccyanide solutions (??60%) was observed at the studied pH range. However, cyanide removal efficiency approached to 100% in Ni(II)?Ccyanide?CEDTA solutions. Formation of Ni(II)?Ccyanide and Ni(II)?CEDTA complexes and relative rates of the reactions of Fe(VI) with various species (water, cyanide, Ni(II)?Ccyanide, and EDTA) present in solutions were responsible for the variation in removal efficiencies in mixtures at various pH. The oxidation of cyanide by Fe(VI) produced cyanate. Tests using electroplating rinse wastewaters demonstrated that Fe(VI) was highly effective in removing cyanide.