Development of a fast and accurate method for testing of nigrosine

Nigrosine reagent is used for maximum elimination of graphitic carbon during flotation of RA Mines lead-zinc sulfide ore to produce Pb and Zn concentrates. The yearly consumption of Nigrosine is ~1400 mt. As of now, there is no chemical method for analyzing its purity. The only criterion for accepting the lot is its more than 99.80% solubility (1% aqueous solution) and its performance to eliminate minimum 92% of the graphite into final tailing. Literature survey undertaken for solution to the problem of purity/specification determination of Nigrosine has indicated the absorbance determination through U V Spectrophotometry method using absorbance property for a colored component of a product and this was selected as an appropriate answer to the problem. The method is simple in application. According to the developed method based on the principle, maximum absorbance of aqueous solution of standard Nigrosine sample in the visible region (400–800 nm) was found to be at 545 nm. Absorbance of each test sample at the same concentration as standard sample was compared at this wavelength and purity of test sample was established in terms of relative absorbance with the standard sample.