Technical and Economical Evaluation of Concentration, Oxidation and Gold Extraction from Sulfide Ore of Chah-Zard

Chah-Zard is a refractory gold ore mine which yields less than 20% recovery in direct cyanidation, due to the encapsulation of a significant portion (80%) of gold within pyrite. This study aims to identify an economic solution for processing of this ore. Initially, the flotation process was performed to obtain a high-grade concentrate. The optimization of the flotation process, considering four factors, was examined through 28 experiments. Four alkaline oxidation experiments, three acidic oxidation tests, and three roasting tests were conducted. Flotation experiments achieved up to 80% gold recovery, aligning with the diagnostic leaching results. This recovery was achieved with 137.5 g/t collector, 525 g/t activator, and 250 g/t dispersant at a particle size of 75 microns (d80). Gold dissolution recovery in the cyanidation of roasted concentrate (650°C and 60 minutes) reached 85%. Optimal operating conditions in the alkaline oxidation process were 70°C, 24 hours, and 35 kg/t sodium hydroxide, yielding 80% gold dissolution recovery on whole ore. In the acidic oxidation process on flotation concentrate with 200 kg/t nitric acid at 60°C and a 5-hour residence time, 68% gold dissolution recovery was achieved. Economic evaluation of the processes based on operational costs indicated that the break-even point for gold grade of the feed for the flotation-roasting process with 68% total gold recovery is 1.2 g/t, for the alkaline oxidation process with 80% total gold recovery is 2.2 g/t, and for the flotation-acidic oxidation process with 54% total gold recovery is 4.2 g/t.