Understanding the discrepancy between prediction and plant GRG recovery for improving the gold gravity performance

Gravity recoverable gold (GRG) content in a sample is typically determined using the standard three-stage test developed at McGill University (Laplante et al., 2000). A comparison of GRG recovery in laboratory with its actual recovery in plants shows that plants recover between one-third and two-thirds of the predicted GRG from laboratory test.Research conducted at COREM seeking the identification and the understanding of potential causes of this discrepancy reveals that particle shape transformation during grinding is a major contributor among other causes such as bleed percent processed, quality of cyclone classification and gravity concentrator operating conditions.To analyze the gold particle shapes and their deportment, samples were collected from different streams of a grinding–gravity (Knelson) circuit in a gold plant and compared to a concentrate sample from a laboratory Knelson concentrator (KC MD3). A particle characterization based on gold morphology was developed to diagnose typical shapes generated in the gold grinding–gravity circuit. The study revealed that the GRG particles reporting to the plant cyclone overflow are the most flattened particles among the samples analyzed and that on the other hand gold particles recovered in the laboratory Knelson concentrator are the least flattened, highlighting the potential cause of discrepancy between the two recoveries.In this paper, the GRG mapping in a conventional grinding–gravity circuit and the transformation of GRG to non-GRG, as mainly explained by gold particle reshaping will be discussed.

Research highlights
► Gold gravity recovery circuits at plant recover between one-third to two-thirds of the recovery predicted by the standard GRG test.
► An understanding of the GRG recovery mechanisms both at plant and lab scale is thus essential for improving the plant gravity recovery performance.
► A case study under this research showed that a staggering 44% of the GRG escapes the grinding-gravity circuit through the cyclone overflow because of the changed gold particle shapes generated during grinding.
► Tracking of particle shapes of the grinding-gravity circuit revealed that gold particles deported to the cyclone overflow are the most flat compared to the gold particles recovered in the laboratory gravity separator highlighting the potential cause of the discrepancy.