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Abstract Strain rate has drawn great research attention in the area of material mechanics. However, thus far the effects of strain rate on the breakage characteristics of rocks or mineral particles were seldom studied. The applied strain rate is one of the key factors causing the variation in breakage environment, and hence the understanding of strain rate's effect on particle breakage is important to the development of a generic breakage model that isolates the rock properties from the breakage environment. This study systematically investigated the characteristics of single particle breakage at different strain rates. The rock samples from four narrow size fractions were used for carrying out impact and compression tests at variable energy input levels. The energy-size reduction relationships for impact and compression breakage were developed, respectively, and the appearance functions for these two breakage mechanisms were also developed based on previous and current work. The results suggest that the sample breaks easier at lower strain rates and the significance of the particle size effect strongly depends on the strain rate. It is demonstrated that the strain rate has an important influence on the progeny size distribution, but the significance of this influence reduces as the energy input increases. It is also found that the sample breaks with a higher energy efficiency at lower strain rates. The strain rate may affect the initiation and propagation of the cracks originate from small flaws and hence results in the difference in the breakage characteristics. Graphical abstract Unlabelled Image Highlights • The sampled ore breaks easier and more energy efficiently at low strain rates • The significance of particle size effect strongly depends on strain rate • Strain rate has a considerable influence on the progeny size distribution • Strain rate is likely to affect the propagation of cracks from small flaws [ABSTRACT FROM AUTHOR]

A new comminution technology that can reduce energy consumption when compared to traditional grinding of rock is presented. The process is based on pulverization driven by transcritical CO 2 cycles, resulting in tensile fracture inside the particle rather than compression from outside. Tensile strength of many rocks is approximately 10 times lower compared to compressive strength offering significant potential for saving energy. In this apparatus, comminution can occur over multiple cycles to enhance rock breakage without extracting and refeeding rock between cycles. The test rig depicts test conditions to capture and to recycle the CO 2. Limestone is utilized as an example material in a lab-scale experimental apparatus. Within the apparatus, the temperature and pressure are raised to supercritical conditions. A rapid release of the CO 2 into a decompression chamber results in an expansion of supercritical CO 2 inside the pores and fractures rock from tension instead of compression. Results show a significant fraction of the limestone is comminuted in three consecutive CO 2 pressure cycles. A majority of the resulting particles exhibit larger fragments from 5 mm to 13.2 mm. 6.2% of the feed material was directly transferred to fine material <300 μm without many intermediate progeny particles. Initial results indicate a larger ratio of the pressure before and after burst, and longer soak times aid pulverization. A single rock is also analyzed, where it is noted that breakage occurs along visible fractures, and this behavior is noted over consecutive cycles. [Display omitted] • Supercritical carbon dioxide migrates into pore structure • Rapid depressurization causes gas expansion and fracture via tensile forces • Generating direct tensile forces offers potential for energy saving • Pressure before and after expansion and soak time influence fracture • Comminution advances with further supercritical CO2 cycles [ABSTRACT FROM AUTHOR]