EXTRACTION OF GOLD(III) FROM LOW-GRADE ORES WITH AMIDINES FOLLOWED BY ITS SPECTROPHOTOMETRIC DETERMINATION WITH METHYLENE-BLUE

A procedure is described in which gold(III) is quantitatively extracted with an amidine into chloroform over the acidity range pH 3.0-11.0 M HCl, followed by its selective spectrophotometric determination by interaction of the extract with methylene blue in the pH range 3.0-9.0. The molar absorptivity of the coloured complex formed by extraction with ten different amidines and methylene blue reaction lie in the range 1.1 × 104-6.5 × 104 1 mol-1 cm-1 at λmax (650 nm) in chloroform. The simplest compound, N, N′-diphenylbenzamidine, was chosen for detailed study. The limit of detection is 5 μg Au l-1. The method is free from interferences from the metals that are generally associated with gold. The method is simple, reproducible and applicable to the accurate recovery of gold from low-grade ores containing the metal at levels of > 1.5 μg g-1. © 1990.