Gravity concentration separates minerals based on density differences. For gold ores, gravity concentrates (jigs, spirals, shaking tables, centrifugal concentrators like Knelson and Falcon) capture the free coarse gold particles upstream of cyanidation. Recovering gold by gravity first means lower cyanide consumption and faster cycle times in the leach circuit downstream.
Why Use Gravity Upstream
Coarse free gold leaches slowly in cyanide — sometimes incompletely. Removing it by gravity first means: (1) immediate gold recovery without cyanide consumption, (2) faster overall recovery, (3) lower cyanide cost. Gravity recovery is typically 10–40% of total recovery depending on ore character.
Equipment
Modern gold gravity circuits use centrifugal concentrators (Knelson, Falcon) that apply high G-force to enhance separation. Shaking tables produce a final clean concentrate. Jigs and spirals are used in some flowsheets. Sizing depends on milling throughput and gravity-recoverable gold (GRG) content from laboratory testing.
Testing for GRG
A GRG test measures how much of an ore's gold can be recovered by gravity at progressive grind sizes. KCA's Reno lab runs GRG tests as part of standard gold-ore characterization. The result tells operators whether a gravity circuit is economically justified before plant design.
Integration
Gravity concentrate is sent directly to the gold room for smelting — bypassing the cyanidation and ADR circuits entirely. The tailings from gravity are then cyanide-leached normally. This split-flowsheet approach maximizes recovery and minimizes operating cost.
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