Ultrafine particles in ground sulfide ores: A comparison of four Cu-Ni ores from Siberia, Russia

• Ultrafine fractions produced by milling the ores were studied.
• Amounts of submicrometer and sub-5 μm particles reached 0.2 vol.% and 3 vol.%.
• The higher yields of the fines were found for Kingash ore and Norilsk valleriite ore.
• Colloids are mainly about 1 μm aggregates enriched in Mg silicates.
• Valleriite and chalcopyrite colloids are stable against oxidation and aggregation.

Nano-, submicro- and micrometer mineral particles may have an important role in beneficiation of metal ores and environmental impact, but their origin and characteristics are poorly understood. Here, we report data for the yield and the composition of fine fractions, and surfaces of several ground Cu-Ni sulfide ores studied using laser diffraction, scanning electron microscopy and energy dispersive X-ray analysis, X-ray photoelectron spectroscopy. Colloidal particles were characterized using dynamic light scattering, zeta-potential measurement, transmission electron microscopy and electron diffraction. The production of fines by dry milling was found to increase from about 0.01 vol.% to 0.2 vol.% for submicrometer particles and from ~ 0.5 vol.% to about 1.5 vol.% for particulate material less than 5 μm in the following order: Noril'sk disseminated low sulfide ore ≤ Noril'sk Cu-rich sulfide ore < Noril'sk valleriite ore < Kingash ore. For wet milling, the yield may be several times higher. Both surfaces of the milled ores and colloids were enriched in O, Mg, Si (largely as serpentine slimes) and depleted in sulfur, basic metals and iron, but colloidal valleriite, chalcopyrite, and oxidized pyrrhotite were found in the respective supernatants too. Typically, the colloidal particles form aggregates with an average hydrodynamic diameter of about 1 μm and a smaller number of ~ 5 μm species, except for valleriite ore, which exhibits a single size distribution peak at 2.7 μm. Zeta-potential, which characterizes the electric charge of the particles and dispersion stability of colloids, changed from − 25 mV for the low sulfide ore to about 0 mV for valleriite ore, and to + 15 mV for Kingash ore. Poor flotation recovery of metal from Kingash ore and Noril'sk valleriite ore is suggested to be due to both the large quantities and positive charge of hydrophilic ultrafine serpentine and/or magnesium hydroxide minerals. Resistance to oxidation and hence stability against aggregation of copper-bearing sulfide colloids in waste waters is expected to result in a negative impact on the environment.

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