Effect of Riffle Height and Spacing of a Sluice Board on Placer Gold Recovery

Sluicing is the preferred mineral processing technique for the treatment of placer gold-bearing alluvium for small scale and artisanal miners in Ghana because sluice board is perceived to be the most cost effective device. However, there are differences in approaches from design to operation. In this work, about 50 kg of ore was obtained from “Peace School” small scale mining site near the University of Mines and Technology, Tarkwa. It was processed to determine the effects of riffle height and spacing on gold recovery. It was confirmed that, in order to trap a greater percentage of gold particles, the height of the riffle ought to be higher than the suspension height of the gold. The suspension heights of the gold particles of the various operational regimes of the sluice board at superficial velocities of 0.5 m/s, 1.0 m/s, 1.5 m/s and 2.0 m/ were 0.9 cm, 1.2 cm, 1.5 cm and 2.9 cm respectively. Analysis of concentrates showed that, 85.4% of gold was recovered during sluicing at approximately 1.0 cm riffle height. The lowest recovery was recorded at 0.5 cm riffle height. Gold recovery was also affected by riffles spacing. For the indicated speeds and the riffle heights the necessary spacing should not be more than 20 cm. The peak recovery was obtained at a riffle height of 1.0 cm but dropped after 20.0 cm spacing.