Time-Dependent Effects of Grind Fineness on Gold Cyanidation Kinetics and Extraction

Abstract

Finer grinding is commonly expected to improve gold cyanidation, but its effect over the full leaching cycle remains insufficiently understood. This exploratory study compared 48-h bottle-roll cyanidation of a low-sulfidation epithermal gold ore ground to 80% and 90% passing 75 μm (P80 and P90), using an initial sodium cyanide (NaCN) concentration of 1500 mg/L. A diagnostic leach test indicated that 89.0% of the gold was operationally cyanide-accessible. P90 required approximately 51% longer laboratory grinding time and produced faster early extraction than P80 (71.0% vs. 49.8% at 2 h), but this advantage diminished over time. At 48 h, P80 reached 94.0% extraction compared with 92.1% for P90, a small difference that should be interpreted cautiously given the9.55% closure bias of the P90 mass balance. Model comparison using the small-sample corrected Akaike information criterion (AICc) most strongly supported the Crundwell-Godorr model for P80 and the Mintek model for P90. The results suggest that finer grinding mainly shifted gold extraction toward the early stage of leaching rather than increasing the extraction achieved within 48 h. A finer grind thus appears most useful when leach residence time is short. Replicated testing is required to confirm these single-run findings.