An investigation of the behaviour of gold in grinding circuits

A 7.6 cm (3") Knelson concentrator was used to estimate free gold content in samples extracted from industrial grinding and gravity circuits. Its recovery was comparable with that of amalgamation and the Mozley Laboratory Separator (MLS). It was then used for a study on gold grinding and classification behavior.Laboratory studies of monosized gold and silica showed that gold produces fewer fines upon grinding: 75% of the mass reports to the next Tyler class, as opposed to 45% for silica. Disappearance from the monosized class (840-1200 $ mu$m) follows first order kinetics for both minerals. However, the rate constant of gold was five to six times lower than that of silica, and folding predominated over actual breakage. Folding yields either spherical or cylindrical particles which flatten upon additional impacting.Smearing of gold onto silica and embedding of silica into gold flakes were observed. It was postulated that gold smearing can lead to metallurgical losses in flotation circuits. A gravity circuit could then increase overall gold recovery.The Knelson concentrator was used to study the behavior of gold in the Hemlo mill grinding circuit. The ratio of the selection function of ore to gold increased from 6 at 50-100 $ mu$m to 20 at 500-1000 $ mu$m. In the primary cyclones, gold's cut size was much finer than the ore, 20 vs. 57 $ mu$m