Particle weakening in high-pressure roll grinding

In the literature, comminution in the roller press and subsequent ball milling has been observed to produce significant energy savings in comparison to ball milling alone. This has been partially—if not totally—attributed to the weakening resulting from compression of the bed of particles in the roller press (also called high-pressure grinding rolls—HPGR). In order to assess, in a more direct way, the ability of high-pressure roll grinding in particle weakening, copper and gold ores crushed in the HPGR and conventional crushing equipment (such as a roll crusher and a hammer mill) have been screened in narrow size fractions and tested singly in the impact load cell. The influences of particle size, specific energy input and position within the bed in the particle breakage characteristics in the HPGR product have been studied. It is found that coarse particles are damaged preferentially and weakening is more significant at higher pressures (and specific energy inputs) in the HPGR if compared to the products of conventional crushing equipment. Particle weakening was found to occur irrespective of the position of the particle within the bed. The greater weakening experienced by coarser particles in the HPGR results in decreasing energy savings with finer size reduction of the product in a subsequent grinding stage.