3.3. Grinding and flotation
The grinding and flotation were conducted at room temperature using Brisbane tap water. 1 kg crushed ore sample at 60% solid density with 10 Kg laboratory stainless steel rods was ground in a tumbling mill to obtain a 80 wt.% passing size (P80) of 150 μm at determined grinding time. Stainless steel was used to avoid iron contamination and the formation of ferricyanide after the addition of cyanide, which may bring additional interference for studying the impact of other cyanide species in flotation. Before grinding, the grinding mill and rods were cleaned by grinding with sands. The mill discharge was transferred to a 2.5 L mechanical flotation cell with an agitation speed of 800 rpm, and the pH of the flotation pulp was modified to 10 before conditioning with any reagents. Then 20 g/t promoter Aerophine 3418A (sodium diisobutyldithiophosphinate) was added at the beginning of flotation and 30 g/t collector PAX (potassium amyl xanthate) was added before the third stage of flotation (after cumulative flotation time of 3 min). 30 g/t Nasfroth 250 as frother was split between the first and third stage of flotation at a ratio of 80/20. Four concentrates were collected at cumulative times of 1, 3, 5, and 10 min with an airflow rate of 6 L/min. The flotation froth was scraped at intervals of 10 s.