Improved derivatisation methods for the determination of free cyanide and cyanate in mine effluent

Generally, the level of cyanide in waste effluents is too high to be discharged into the environment. Consequently, treatment regimes are necessary in order to protect the environment. However, the cost of most of the treatment methods is expensive and not sensitive enough and, therefore, cannot always be justified. In this research, cyanide speciation products, free cyanide (CN−) and cyanate (CNO−) were determined by highly sensitive derivatisation methods followed by spectrometric analysis. Spectral scans were carried out for pure and environmental samples derivatives in order to evaluate the possibility of interfering species. For CN− a linear range from 0.01 to 80.0 mg/L was determined. In the case of CNO−, the linear range was between 0.02 and 80.0 mg/L. The detection limits were 0.05 and 0.20 mg/L for CN− and CNO−, respectively. These values are in good agreement with those reported in literature. The concentration ranges of the speciation products in environmental samples were 0.70-52.0 mg/L and 0.50-76.0 mg/L for CN− and CNO−, respectively. These values were well above their acute toxicity levels. Increase in cyanate levels in the effluent with time was clearly observed while the concentration of cyanide decreased. This was attributed to the oxidation of CN− to CNO−.