Optimization of the spectrophotometry determination of Aqueous Cyanide: Application on Samira (Niger) Gold Mine Groundwater Analysis

摘要

Cyanide is very toxic to humans, and its usage in gold mining potentially poses serious environmental threats. In this paper, by revising the well-known colorimetric method based on the chlorination of cyanide with chloramine-T and subsequent reactions with pyridine-barbituric acid reagent, we have developed a robust and sensitive UV-Visible spectrophotometric method for cyanide determination in aqueous media. The optimization of some analytical parameters, like the duration of the colored complex formation (50 min), the amount of chloramine-T (1 mL) and the medium sodium hydroxide concentration (0.05 M), has allowed us to highly improve the stability and exaltation of the colored complex absorption signal. The obtained limits of detection (LOD) and quantification (LOQ) are respectively 0.2 and 0.7 μg L~(-1). In addition to this sensitivity, our approach seems to be one of the most reliable methods for free cyanides determination in environmental matrices. The recovery rate in spiked solutions is more than 95%. Application on thirteen (13) groundwater samples (drillings, piezometers and open pit mining waters), adjacent to and around the Samira (Niger) gold mine, has shown that the obtained cyanide rates are less than the World Health Organization (WHO) bWnking-water quality guideline value (70 μg L~(-1)). Nevertheless, the observed values indicate a potential contamination of the ground water resources, which previously not contained this pollutant.