A comparative study of gold refractoriness by the application of QEMSCAN and diagnostic leach process

Abstract

Quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) and diagnostic leaching (DL) are the two main methods to evaluate the gold refractoriness nature. Limited availability of QEMSCAN or its cost sometimes can be the drive to use DL method, or vice versa.

We present the results of a comparative study that investigates and compares the origin of the refractoriness of two different gold samples with QEMSCAN and DL. As a baseline, the gold recovery values of samples 1 and 2 via the standard cyanidation process over a leaching period of 24 h were 74% and 54%, respectively. Based on the DL tests, the refractoriness of samples 1 and 2 was mostly related to the fine dissemination and association of the electrum (Au-Ag alloy) and gold telluride with the sulfide minerals, particularly pyrite. The QEMSCAN analysis provided more details about the gold deportment in the two samples. The QEMSCAN results showed that the gold in the two samples was mostly present as electrum and gold-telluride. In sample 1, about 89% of the gold occurred in the form of electrum with a 63% Au and 36% Ag composition. The main gold form in sample 2 was gold-telluride (81%). Energy dispersive X-ray spectroscopy (EDS) results demonstrated that the gold telluride phase was in the form of calaverite (AuTe₂) in both samples. The QEMSCAN results suggested that 77% of gold in sample 1 and 88% of gold in sample 2 were liberated or locked in the sulfide minerals, and the balance was the solid solution gold. Based on the QEMSCAN study, the total liberated gold and the gold locked in the sulfide minerals are expected to be amenable to cyanide leaching after a complete sulfide oxidation process, i.e. pretreatment. DL tests, however, suggested that 91% of the gold in sample 1 and 87% of the gold in sample 2 were leachable after the oxidation of sulfides in the two samples.

Lastly, the two samples were pretreated by (1) roasting, and (2) atmospheric oxidation to oxidize sulfide minerals and render the samples more amenable to cyanide leaching. The gold recoveries of the roasting calcines by cyanidation were 93% and 76% for samples 1 and 2, respectively. The cyanidation of the atmospheric oxidation residues provided a greater gold recovery for both sample 1 (96%) and sample 2 (85%). Gold recovery for sample 1 was underestimated by QEMSCAN, however the gold recovery values were estimated well by DL.