Nitric Acid Treatment of a Pyrite Rougher Concentrate to Oxidise Differentially the Pyrite Types and Modify the Au:S Ratio in a Resulting Cleaner Concentrate

•Refractory gold ores may contain gold-rich pyrite and low gold pyrite types.•Novel hydrometallurgical approach developed to modify surfaces of pyrite types.•Treatment with nitric acid oxidises surfaces of different pyrite types differentially.•Subsequent flotation tests show beneficial upgrade in the concentrate Au:S ratio. The Lihir ore deposit is a sulfide associated refractory gold ore of epithermal origin containing different types of pyrite with a range of levels for gold. The presence of the low gold pyrite types decreases the Au:S value of the Lihir ores and its concentrates resulting in higher consumption of oxygen in the autoclave and thereby affecting the overall gold production at Lihir. This research, deriving from the fundamental principles of hydrometallurgy, is an attempt to develop a manipulative framework to modify the flotation response of gold-rich pyrite and low gold pyrite so that the Au:S ratio of the final pyrite concentrate from flotation can be upgraded. Metallurgical results confirmed that it is possible to upgrade the Au:S values of a pyrite flotation concentrate by using a hydrometallurgical scheme for preparation before flotation. A 144% increase in Au:S value was obtained with 25% oxidation of the pyrite concentrate with a gold recovery of 56%.