Effect of Ashless Polymer Binders on the Strength and Leaching Behaviour of Pelletized Pyrite Concentrate

The development of cyanide-free technologies for processing refractory pyritic materials requires an effective pretreatment stage capable of improving both the mechanical stability and leachability of the feed material. This study investigates the influence of binder type and concentration on the properties of pelletized pyrite concentrate and its subsequent response to thiosulfate leaching. A pyrite concentrate from the Almalyk Mining and Metallurgical Complex containing 4.0–4.5 g t⁻¹ gold was pelletized into 3–5 mm granules using 1–3 wt.% kaolin or the ashless polymer binders SK-D and SK-K. The pellets were dried at 105 °C and thermally treated at temperatures up to 600 °C for 60 min. Their mechanical strength was evaluated by axial compression, while the formation of gold–thiosulfate complexes in the leach solutions was examined by UV spectrophotometry. Pellet strength increased with both roasting temperature and binder concentration. At 600 °C, the highest compressive strength of 1.65 MPa was obtained with 3 wt.% SK-K, whereas pellets containing 3 wt.% SK-D and kaolin exhibited strengths of 1.48 and 1.28 MPa, respectively. Preliminary thiosulfate leaching tests showed more intensive absorption bands for the polymer-bound samples than for the kaolin-bound material. In particular, the SK-K sample exhibited a pronounced absorption maximum at 305 nm, indicating favourable formation and stability of the [Au(S₂O₃)₂]³⁻ complex. The results demonstrate that ashless polymer binders improve pellet integrity without diluting the valuable mineral fraction and create more favourable structural conditions for subsequent gold leaching.