The mercury “tromol” mill: an innovative gold recovery technique, and a possible environmental concern

In Indonesia and other developing countries, an ingenious pebble mill and amalgamation drum serves both for gold production and bulk sample assay. Known as “tromol” mills, these locally-fabricated devices are carried to remote mountain areas for frontier small-scale mining and basic prospecting. Many hundreds of tromol drums now turn at plants in rural areas.The steel drum is filled with a standard quantity of rock, topped with hard river cobbles, and rotated by an engine or water power. Mercury, imported illegally at high cost, is added to amalgamate gold and silver Waste, containing any lost mercury, typically washes into streams. Limited studies in North America and Russia suggest some biological uptake occurs from metallic mercury lost long ago by obsolete gold processing methods. Levels regarded as hazardous are noted in river fish in Nevada and Quebec, but no major health problems are attributed to mercury from gold mining in temperate climate regions. No published data on mercury discharges in Indonesia was found. Application of simple metallurgical techniques at Indonesian mining camps could greatly decrease mercury (and probably also gold) loss.