I decided to do some research on the gold extraction methods discussed in the USAID document (https://investorshub.advfn.com/boards/read_msg.aspx?message_id=132657752). The following terms are used on pages 12 & 13 when the extraction methods are discussed. Let's dive into these terms and find out exactly what they mean:
"The gravimetric concentrator, amalgamation and cyanidation were determined as the best processes......During 2004, the lixiviation system was change to a cyanidation with mechanical shaking, being also modified the precipitation method by the Merrill-Crowe, boxes with zinc dust in a free oxygen atmosphere. This change provides the decrease from 30 to 3 days of lixiviation time lapse with the recovery of the gold in the mud..."
-gravimetric concentrator: Table type video:
Centrifugal type video:
Fully automated table type gravity separator:
-amalgamation and cyanidation & Merrill-Crowe method: Here's a video from 1973 that details these processes:
A few words about the use of cyanide: While toxic, cyanide is not a long-term environmental pollutant. It breaks down in the environment within a few days and repeated non-lethal doses of cyanide can be tolerated by humans and other organisms without long-lasting health impacts. https://www.smenet.org/docs/public/SafeAndEffectiveUseOfCyanideInTheMiningIndustry.pdf http://www.cyanidecode.org/cyanide-facts/environmental-health-effects -"Cyanide does not accumulate or biomagnify, so chronic exposure to sublethal concentrations of cyanide does not appear to result in acute toxicity......There is no evidence that chronic cyanide exposure has teratogenic, mutagenic or carcinogenic effects".