Reducing mercury usage in artisanal gold mines using grinding and sieving

Abstract

Gold extraction in primitive artisanal mines usually involves the over-usage of mercury (Hg). This practice results in significant environmental contamination, but is difficult to eliminate due to its effectiveness. Any alternative must be simple, inexpensive and visually effective. This paper proposes a novel, chemical-free method for extracting gold from gravity middlings which has potential as an effective alternative to Hg amalgamation. This method exploits the differences in relative malleability, rather than density, of gold and waste products by submitting concentrates to grinding in a rod mill. The grind products are separated through a sieve, where flattened gold particles are captured on the oversize while brittle waste reports to the fines. Recoveries often exceeded 90%, with nearly pure raw gold separated after only minutes of grinding. While recently adapted to the modern Yukon placer fields, this method has potential to reduce Hg usage by miners in more primitive settings.