Effect of ethylenediaminetetraacetate on the oxidation of cyanide in an electrochemical process.

The effect of ethylenediaminetetraacetate (EDTA) on the removal of cyanide (CN-) from electroplating wastewater was investigated using an electrochemical process. Decay of 100 mg/L CN- was carried out as a function of electrical current (I = 0.5-5.0 A) and molar ratios of EDTA to CN- (2.6-15.7) at pH 13.0. The experiments showed that electrooxidation of CN- follows first-order kinetics with respect to CN- ion. The first-order rate constant, k, showed linearity with the applied current (r(2) = 0.99). At a molar ratio of 2.6 ([EDTA]: [CN-]) and electric current, I = 2.5 A, the oxidation of CN- proceeded by a slower rate than in the absence of EDTA. Under similar conditions, the oxidation rate of cyanide increased at molar ratios ranging from 5.2 to 15.7. Consequently, the energy consumption for the electrooxidation of CN- varies with the amount of EDTA present in the solution.