Effect of Particle Size on Porosity by Bulk Density and Computed Tomography (CT) Scanning Methods

摘要

Fluid flow plays a critical role in the metal extraction using heap/dump leaching. The behavior of fluid flow is greatly influenced by the porosity of the packed ore beds. The effect of particle size distribution on porosity was quantified by two methods: bulk density measurement and computed tomography (CT) scanning technique. Porosities under three particle gradation conditions were studied: narrow-sized, well-graded, and gap-graded. For narrow-sized particles, the porosity measured by the bulk density method decreased as the particle size was increased until a limit was reached. For the loose packing the porosity increased from about 36 % to 52 % as the mean grain size decreased from 1 mm to 45 ?m. This was different from the case of the close packing, where the porosity was observed to increase from 38 % to 52 % in a rather narrow size range from 100 ?m to 45 ?m. The results obtained by the CT scanning method showed a similar trend: the porosity decreased with increasing particle size. The porosities of the well graded particles were lower than those of the narrow-sized particles, indicating that the well graded particles were more susceptible to compaction. For gap graded particles, the results obtained using the two methods showed that the porosity initially decreased as the fraction of the fine particles added was increased; as the fraction of fine particles was further increased, the porosity started to increase. In general, in the three cases studied, the two methods generated consistent results. The results have important implications for understanding the behavior of fluid flow in the metal extraction using heap/dump leaching.