Effect of magnetite content on Bond work index and preconditioning: Case study on Chadormalu iron ore mine

Grinding is one of the most costly operations in the mechanical breaking and mining. Determination of the breakage characteristics and preconditioning is important to increase the grinding efficiency. Investigations of the seismic, mechanical and breakage properties of iron oxides are very important parameters for investigating the rock fragmentation by blasting and comminution processes in iron ore mines. In this paper, at first, geomechanical and seismic properties of the oxide ores (magnetite and hematite) in the Chadormalu iron ore mine were studied. The results showed that the percentage of magnetite has a direct relationship with uniaxial compressive strength, tensile strength and P and S wave's velocities and has an inverse relationship with Poisson ratio and porosity. Moreover, to study breakage and preconditioning characteristics in the iron ores, two samples with different magnetite percents were blasted by detonation cord. The results showed that with higher percentage of magnetite, the number of fractures induced by blasting increased. Bond work index and magnetite percent were investigated in the 430 blasts in the mine. This investigation not only confirmed the small scale blasting results, but also showed that increasing the magnetite percent up to 50% noticeably reduces Bond work index and energy consumption in the grinding process. Also, the relationship between muck pile fragmentation and magnetite percentage were studied for several blasts that had the same blast pattern parameters and similar geology conditions. These results also confirmed precedents conclusions regarding magnetite percent and preconditioning relationship.