Study of the colloidal-chemical and depressing characteristics of a micro- and nanosized depressant based on magnetite

• The proposed depressant - Fe 3 O 4 activates O 2 and convert it into reactive forms due to its paramagnetic properties. • The resulting reactive oxygen species oxidize the galena surface, rendering it hydrophilic and non-floatable. • Micro- and nanosized magnetite decreases galena recovery while maintaining high chalcopyrite recovery. • Cu concentrate with a grade of 28.6% Cu (71.5% recovery), Pb concentrate with a grade of 45.3% Pb (85.3% recovery). • Cu–Pb separation is achieved at pH 5.5–7.5 with a low magnetite dosage (15 g/t). In this paper, magnetite was proposed as a flotation depressant for the selective separation of chalcopyrite from galena. Micro- and nanosized magnetite particles were synthesized via the chemical co-precipitation method using divalent iron and iron(III) chloride. The chemical composition, surface properties, and morphology of the synthesized magnetite were investigated using Fourier-transform infrared spectroscopy and scanning electron microscopy techniques. The adsorption properties of the surface groups of magnetite on mineral surfaces were examined by measuring the contact angle, including the electrokinetic potential. The ζ-potential measurements indicated that the micro- and nanosized magnetite particles exhibit a selective and strong depressing effect on the flotation of galena, while having a negligible impact on the flotation of chalcopyrite. The contact angle with the galena surface decreased from 94.52° to 42.70° under optimal conditions. A possible model for the adsorption of magnetite particles at the water–solid interface of the two minerals was proposed. The article demonstrates that micro- and nano-sized magnetite particles can potentially serve as an effective, non-toxic depressant for the flotation separation of Cu–Pb bulk concentrates from polymetallic sulfide ores containing galena. When using known paramagnetic oxide materials in the form of plates, spirals, or with particle sizes above 100 µm, the separation of copper–lead concentrate into individual fractions occurs within a narrow pH range of 5.6–5.8, without requiring iron sulfate or sodium sulfite. However, to broaden the effective pH range and increase the specific surface area of the paramagnetic material, powder-form magnetite with particle sizes of 5–20 µm was employed. As a result, the separation of copper–lead concentrate occurred more distinctly at a pH range of 5.5–6.5, with a dosage of 1–1.5 kg/t of concentrate. In our case, the use of micro- and nanosized magnetite enabled effective separation of copper–lead concentrate within a broader pH range of 5.5–7.5 and at a significantly lower reagent consumption. At an optimal dosage of 15 g/t of the proposed micro- and nanosized magnetite depressant for galena, a copper concentrate with a copper grade of 28.6 % and a recovery of 71.5 % was obtained, and a lead concentrate with a lead grade of 45.3 % and a recovery of 85.3 % was achieved. The content of lead in the copper concentrate and copper in the lead concentrate did not exceed 5 %.