This study investigated the flotation performance of W8, a blended xanthate collector containing ethyl, butyl, propyl, and amyl xanthates, combined with ammonium dibutyl dithiophosphate (ADD) for treating low-grade arsenopyrite-type gold ore from Golmud, Qinghai. Real ore flotation tests demonstrated the superior efficacy of the W8 + ADD system, achieving 84.06% gold recovery with 0.34 g/t tailings, outperforming conventional sodium amyl xanthate (SAX) + ADD and sodium propyl xanthate (SPX) + ADD systems. Systematic studies on pure arsenopyrite revealed a significant synergistic effect in the mixed SPX-SAX system (1:4 ratio), representative of W8 composition. At pH 9, the mixed collector achieved 73.5% recovery, substantially higher than individual SPX (37.5%) or SAX (45.8%). This enhanced performance was attributed to improved surface hydrophobicity (contact angle 47.68° vs. 36.92° for SAX), greater adsorption density (4.97 × 10⁻⁷ mol/g under depressant conditions), and extensive formation of molecular aggregates observed via AFM, which increased surface roughness to 28.95 nm. Flotation kinetics further confirmed the advantage of W8 + ADD, which reached 72.1% cumulative recovery in 420 s, exceeding both mixed SPX/SAX (69.5%) and single SAX (65.5%) systems. The synergistic interaction among different xanthate components in W8 enables efficient recovery of gold from this refractory ore.

The flotation of fine mineral particles is always a difficult problem. The flotation of fine arsenopyrite particles (−20 μm) in a sodium butyl xanthate (SBX) system was studied by using polyethyleneimine (PEI) as a flocculant. The flocculation properties of PEI on fine arsenopyrite were studied using sedimentation tests. The results showed that the optimum pH for the sedimentation of PEI was approximately 7.5; the higher the molecular weight (M.W.) of the flocculant, the better the sedimentation effect. In the flotation experiments, it was found that the flotation recovery of PEI-3 with high M.W. as flocculant was only 57%, while the flotation recovery of PEI-2 with medium M.W. was 90% under respective optimum conditions. The contact angle tests showed that the natural contact angle of arsenopyrite was 37°; the addition of moderate PEI-2 had a slightly negative influence on the hydrophobicity of arsenopyrite in the SBX system. From the size analysis results, the maximum particle size (D₁₀₀) and median size (D₅₀) of the arsenopyrite increased from 20 and 11 μm to 48 and 28 μm after treatment with 40 mg/L PEI-2, a size more conducive to bubble capture. From the combination of these results, it can be concluded that PEI-2 improved the flotation of fine arsenopyrite mainly by increasing the particle size to a suitable range through flocculation. The XPS results indicated that the adsorption of PEI-2 on the arsenopyrite surface was due to the chemisorption between the imino group and the active Fe/As sites. Applying PEI-2 to a fine disseminated arsenopyrite-type gold ore, a concentrate containing 36 g/t Au with a Au recovery of 88% can be obtained.

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.

The effects of ZnSO₄ on arsenopyrite depression were studied with sodium carbonate and sodium isobutyl xanthate (SIBX) as the pH regulator and collector, respectively. In both micro and real ore flotation tests, ZnSO₄ showed better depression on arsenopyrite (pH 7.5–9.0 adjusted by Na₂CO₃) compared with sodium humate. The depression mechanism of ZnSO₄ on arsenopyrite flotation was studied by electrokinetic potential, adsorbed amount measurements, scanning electron microscope (SEM) observation and energy dispersive spectra (EDS) detection. The electrokinetic potential measurement results show a potential increase forpleas the arsenopyrite treated with ZnSO₄ in the pH range 7.5–9.0, which could be attributed to the formation of the precipitated zinc carbonate (ZnCO_3(S)). For arsenopyrite treated with both ZnSO₄ and SIBX, the electric surface potentials also display an increase, to approximate the values with solely ZnSO₄ treated, at pH 7.5–9.0, indicating the inhibition of ZnCO_3(S) upon the SIBX adsorption onto arsenopyrite. Adsorption results demonstrated that SIBX adsorption onto arsenopyrite indeed was inhibited at the pH 7.5-9.0 through the sharp decrease in SIBX adsorbed amount with ZnSO₄ as the depressant at this pH range. SEM observation and EDS detection results verify the formation of colloidal ZnCO₃ on the arsenopyrite, with ZnSO₄ as the depressant in combination with Na₂CO₃.