Correlation between the top of froth grade and the operational variables in rougher flotation circuits

Abstract Cu grades at the top of the froth (TOF) were compared to the froth depth ( h F ) profiles and froth discharge velocity profiles along rougher flotation circuits. Measurements were performed in two self-aspirated flotation banks, one consisting of nine 130 m 3 cells (1-2-2-2-2 arrangement), and the other one of six 250 m 3 cells (1-1-1-1-1-1 arrangement). Two behaviors for the TOF grade were observed: (i) for h F  ⩽ 10 cm, a decrease in the TOF grade along the bank was observed because either the decrease in mineral liberation or a potential recovery of slow floating gangue, (ii) for h F  ⩾ 10 cm, an increase in the TOF grades with the froth depth was observed, mainly due to an increase in froth selectivity. In addition, an inverse relationship between TOF grades and froth discharge velocities was obtained in most cases. However, in the first rougher cell, both higher froth discharge velocities (7–14 cm/s) and higher TOF grades (20–28%Cu) were observed. The froth in the first cell is typically loaded, which favors the froth stability as well as the concentrate discharge velocity. The TOF grades of Mo as a function of the operating variables showed the same dependency as those observed with the TOF grade of Cu. This result indicated that Cu and Mo minerals had similar flotation rates in the rougher operation, which was in good agreement with the comparable ranges of Cu and Mo rougher recoveries.