Effect of pH, air velocity and frother concentration on combustible recovery, ash and sulphur rejection using column flotation

This study shows the effect of pH, air velocity (Jg) and frother concentration (FC) on combustible recovery, ash and sulphur rejection for four Colombian bituminous coals: Cerrejَn (Guajira), Nechي (Antioquia), Jagua (Cesar) and Guachinte (Valle del Cauca) using column flotation. For the experimental development a 23 factorial central composite experimental design was used. The coal samples were processed in a pH range of 4 to 10, Jg in the range of 0.7 to 2.1 cm/s and FC in the range 2.1 to 6.3 kg/t. Results showed that Cerrejَn and Jagua coal presented combustible recovery higher than 50%, (57.6% and 54.7% respectively), at acidic pH (pH 5), with Jg of 1 cm/s and 3.2 to 4.2 kg/t of FC, respectively, while Guachinte coal presented a maximum combustible recovery of 56.4% at alkali pH (pH 9), Jg of 1 cm/s and 3.2 kg/t of FC and Nechي coal obtained the highest combustible recovery (46.8%) at pH 7 with 2.1 kg/t of FC and Jg of 1.4 cm/s. For Guachinte and Nechي coal ash and sulphur rejection were high (90.3% and 88.5%) and (71.3% and 73.8%) respectively at acidic conditions (pH 4 and 5) with Jg in the range of 1.4 to 1.8 cm/s, whereas Cerrejَn and Jagua coals exhibited high values of ash (85.4% and 94.7%) and sulphur rejection (81.1% and 85.1%) at alkali conditions (pH 9 and 10) with Jg in the range of 1.0 to 1.4 cm/s. In general, it was observed that Cerrejَn and Jagua coals presented higher values of combustible recovery under acidic conditions than Nechي coal and Guachinte coal.