System-Wide Evaluation of Gold and Silver Recovery and Mercury Losses in an Artisanal Amalgamation–Cyanidation Circuit: A Diagnostic Approach to Mercury-Free Processing

Despite decades of intervention efforts, mercury amalgamation remains widespread in artisanal gold mining (AGM), yet no prior study has presented an integrated metallurgical balance quantifying gold (Au), silver (Ag), and mercury (Hg) simultaneously across both the amalgamation and cyanidation stages of a single processing circuit. This study addresses this gap by evaluating an artisanal amalgamation–cyanidation operation in Pernambuco, Brazil, through systematic sampling, fire assay and ICP-OES analyses, grain size distribution, and SEM-EDS mineralogical characterization. The whole-ore amalgamation (WOA) stage recovered 44.7% ± 11.7% of Au and 11.5% ± 15.4% of Ag from a feed grading 2.96 ± 1.53 ppm Au and 8.09 ± 1.65 ppm Ag. Subsequent vat cyanidation of the Hg-contaminated tailings recovered 75.8% ± 4.32% of the remaining Au and 32.9% ± 9.24% of Ag, raising overall recoveries to 86.6% ± 2.89% for Au and 40.6% ± 4.58% for Ag. Although both stages contribute meaningfully to gold recovery, under the operating conditions evaluated, cyanidation contributed more substantially to overall Au recovery than whole-ore amalgamation. SEM-EDS identified free amalgamated electrum particles in the tailings, attributed to excessive pulp density (≈43% solids) impairing particle settling on the amalgamation plates. These inefficiencies led to estimated mercury losses of 262 g/day, yielding a Hg(lost):Au+Ag(produced) ratio of 5.5. Based on this diagnostic evidence, replacing whole-ore amalgamation with optimized comminution followed by gravity concentration is identified as a technically promising mercury-free pathway requiring pilot-scale validation.