Impact of Carbonaceous Gangue Removal on the Flotation Performance of a Polymetallic Base Metal Sulphide Ore

One of the mines in the Northern Cape of South Africa is currently producing galena and sphalerite concentrates from a polymetallic sulphide ore using differential flotation. Currently, the concentrate grade does not meet the target grade requirements of the Pb and Zn concentrates. The current work investigated the enhancement of the grade and recovery of Pb and Zn by implementing a four-stage flotation process which included a carbonaceous gangue removal first stage. During the gangue flotation stage, Pb and Zn were depressed using ZnSO₄ and NaCN. Aero 3418A was used at the Pb flotation stage as a collector while Zn was depressed. At the Zn stage, CuSO₄ was used to activate Zn while SIPX was used as a collector and pH was adjusted to 12 with CaO. Taguchi's design of experiments was used to optimize the reagent dosages. The ore samples from the East Pit showed higher Pb and Zn grades of 1.1% and 9.38%, respectively, whilst the samples from the West Pit had Pb and Zn grades of 0.66% and 5.92%. Pyrite was the most crystalised mineral in both samples, according to the XRD data, followed by sphalerite, quartz, and galena. Since 32% C removal was reached in the gangue removing stage in the East Pit and 63.6% in the West Pit, the East Pit proved challenging to treat. The two highest Pb recoveries and grades were 70.9% with an 11% grade (West Pit) and 61.1% with a 16.8% grade (East Pit). The West and East Pit samples yielded recoveries of 92.5% and 89.6% for zinc, respectively.