Vibra Screw Feeder used in separation technique for removing gold and silver from the mining solution.

The Merrill–Crowe Process is a separation technique for removing gold and silver from the solution obtained by the cyanide leaching of precious metal ores. This process is currently used at the 10 largest gold producing mines in the free world. As part of the process, zinc dust is added in small amounts but due to the variation in gold to silver ore ratio the amount of zinc need fluctuates and needs to be precisely fed to maintain steady state process.

Zinc dust has a bulk density at 220 lbs/ft3, with a particle size of 2-9 micron. The feed rates are low between 8 to 35 kg/hr. The material will settle out, de-aerate and become a non-free flowing powder. Over the years Vibra Screw has developed a Loss-In-Weight feeding system which incorporates its vibrated Versi Feeder which uses controlled vibration to assure consistent flow of material from the hopper through the feed screw and into process. The Live Bottom Bin above the feeder stores a shift worth of material and discharges the material to the feeder when the control system requires. Vibra Screw has been providing feeders for over 40 years to gold extraction processes.