Ultrasound activation of microwave-induced damage for enhanced grindability and mineral liberation in a polymetallic ore

This study investigated microwave irradiation followed by ultrasound treatment as a combined pretreatment route to improve the comminution of a polymetallic ore. Samples were exposed to microwave powers of 700, 1100, and 1600 W for 30 to 150 s, and selected conditions were subsequently treated by ultrasound for 3 to 12 min. The response was assessed by the relative work index, first-order grinding kinetics, X-ray microtomography, and scanning electron microscopy image analysis of Fe- and Cu-bearing mineral exposure. Microwave pretreatment improved grindability mainly through internal weakening, with limited changes in feed size before grinding. Under the adopted 30 s laboratory grinding test, which produced a relatively modest change in particle size, the most pronounced microwave-only response was observed at 1600 W, with relative work index values of approximately 54–56 %. Ultrasound alone did not produce a meaningful improvement, but ultrasound applied after microwave pretreatment further reduced the index to about 47 %, with most of the gain achieved after 6 min. Grinding kinetics showed that microwave irradiation increased the specific breakage rate by about 20 % at 1600 W, whereas ultrasound caused only minor additional changes in the top-size breakage constant. X-ray microtomography revealed an increase in detectable void fraction from nearly zero in untreated and ultrasound-only samples to 0.45 % after microwave treatment and 1.86 % after the combined treatment. Within the analysed −0.85 + 0.60 mm size fraction, the mean area fraction of Fe- and Cu-bearing minerals per particle increased from 9.26 % in the control to 18.15 % after the most effective combined treatment. These results show that ultrasound acts mainly as a damage-activation step, intensifying microwave-induced defects and enhancing both grindability and mineral exposure.