Gold recovery improvements in grinding and flash flotation circuit

Grinding and a flash flotation cell are frequently installed to recover fast floatability coarse particles avoiding their regrinding. However, the ore textural characteristics, such as grain size, change during mine operation and consequently the recovery of valuable particles in the flash flotation cell decreases. This article proposes and validates an interesting method of solving the problem of low gold recovery, making relevant and well thought out changes in a grinding and flash flotation circuit. This was done by optical ore characterisation (Leica DM2700 P microscope using 20X and 40X lens), mathematical modelling, and steady state process simulation (evaluating the original circuit (simulation I) and two proposed circuits (simulation II, and III)). The mineralogical characterisation indicates that, liberated gold (Au), electrum (Au-Ag), and acanthite (Ag₂S) particles of less than 100 µm were the desired particles in the flash concentrate. Additionally, true flotation was identified as the predominant mechanism in gold and silver recovery, but mathematical model suggests that a small fraction of fine particles with gold could be recovered by entrainment. Both analyses led to the proposed installation of a re-grinding mill with recirculation to a flash cell (simulation III). After its commissioning, gold recovery in the flash cell increased 27.0%, reaching a maximum of 48.3%. This represents a clear improvement in gold recovery in a single stage. A significant increase in the global gold recovery was also observed (from 78.9% to 90.6%).