Size-by-size analysis of dry gravity separation using a 3-in. Knelson Concentrator

Centrifugal concentrators have been widely used to recover fine gold over the past few decades, the main drawback being the large volume of water required during the operation. As water is an increasingly important commodity, investigating dry processing to reduce water usage is of great importance. This work investigated using a laboratory scale Knelson Concentrator with a dry feed, and air being used to replace water as the fluidising medium and size-by-size testing of material. A synthetic ore comprised of tungsten and quartz was used to mimic a gold ore. Response surface methodology and central composite design were used for modelling and optimisation with the experimental variables being the motor power (MP) (%), air fluidizing pressure (AFP) (psi) and solid feed rate (SFR) (g/min). The observed results of the three size classes indicated that amongst the three variables; the motor power had the greatest impact when comparing to the other two variables. Different optimum conditions had been found for −425 + 150 μm, −150 + 53 μm and −53 μm size fractions and these are 30% MP, 200 g/min SFR and 10 psi AFP, 50% MP, 160 g/min SFR and 11 psi AFP, 65% MP, 200 g/min SFR and 11 psi AFP, respectively.