Estimating specific energy from the brittleness indexes in cutting metallic ores

Specific energy (SE) is a very useful parameter for assessing rock excavation by machine. Predicting the SE from the brittleness will be practical, especially for preliminary studies, due to the fact that determining the SE from cutting tests is difficult and expensive. In this study, the predictability of the SE from different brittleness concepts was investigated for metallic ores such as chromite, haematite, galena, and smithsonite. Uniaxial compressive strength, Brazilian tensile strength, impact strength, and small-scale cutting tests were carried out in the laboratory. The SE values were calculated from the cutting tests and correlated with three different brittleness concepts. A significant correlation could not be found between the SE and the brittleness B3 (the ratio of compressive strength minus tensile strength to compressive strength plus tensile strength). However, strong correlations were found between the SE and the both brittleness B5 (the product of percentage fines in the impact strength test and compressive strength) and brittleness B8 (half of the product of compressive strength and tensile strength). The validations of the derived equations were also checked. It is concluded that the SE in ore cutting can be reliably estimated from the brittleness concepts B5 and B8.