Fenugreek Polysaccharide Gum as a Depressant in the Flotation Separation of Gold Ore with a High Content of Clay Minerals

A gold mine located in western China is facing the problem of a low concentrate grade, significantly hindering its economic benefits. Preliminary assessments indicate that this is caused by gangue minerals that are prone to floating and sliming, necessitating suppression in the flotation process. The effect of fenugreek polysaccharide gum (FGM) upon the flotation separation of arsenopyrite (representative of Au-bearing minerals) and pyrophyllite (a typical gangue mineral) was investigated; its industrial potential was verified through actual ore flotation and pilot plant testing. Additionally, the selective inhibition mechanism of FGM on pyrophyllite was elucidated. The flotation tests of pure minerals indicated that pyrophyllite has a high natural floatability; thus, it cannot be separated from arsenopyrite at low alkaline pH (7–9); smaller pyrophyllite particle sizes, especially −0.038 mm fractions, significantly decreased the arsenopyrite recovery; FGM can eliminate this adverse effect to a large extent through its selective depression of the flotation of pyrophyllite. For real ore systems, FGM also exhibited superior performance compared with the commonly used silicate and SHMP; closed-circuit flotation tests showed that the gold grade of the concentrate increased by 3.90 g/t and the enrichment ratio increased by 2.53 with the addition of FGM. As of now, FGM has increased the profits by USD 1.715 M in the past two years by improving concentrate grade and recovery efficiency. According to the results of contact angle, zeta potential, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), the selective adsorption of FGM onto the pyrophyllite surface was the reason for the positive effect; the interaction primarily involved the Al sites on the pyrophyllite surface and the –OH on FGM molecules.