Bulk density: : neglected but essential

• Autores: Andrew Scogings
• Localización: Industrial Minerals, ISSN 0019-8544, Nº. 571, 2015 (Ejemplar dedicado a: Abril)
• Idioma: inglés
• Texto completo no disponible (Saber más ...)
• Resumen

  • In practical terms, the bulk density of a powder tends to increase the more it is subjected to tapping, vibration or other action which causes particles to become better packed, with less void space between larger particles; this is known as the 'tapped bulk density'. Bulk density of free-flowing powders/granular materials can be determined by filling a container of known volume, at which stage the material is weighed and the 'loose bulk density' can be estimated. The container is then tapped and refilled until the material stops settling, at which stage the tapped bulk density can be estimated.

    A further example from the chromite mine concerns pyroxenite drill core from the chromitite hanging wall, which the mine planners wished to evaluate for an open pit situation. In this case the pyroxenite ranged from weathered (friable and porous) to fresh (competent and non-porous) hence there were several options, including water displacement of sealed samples and the calliper method. An unweathered pyroxenite core sample was chosen as a control and density was estimated using the calliper and various water displacement methods. The calliper method yielded comparable results to the Archimedes method (uncoated, vacuum packed and paraffin wax yielded DBD ~ 3.3 t/m[superscript]3 ). However the 'cling wrap' method proved to be unreliable as it entrained air (reducing the density) and was not 100% waterproof.

    An alternative drilling method had to be considered in order to measure ISBD and, after discussion with the contractor, the RAB rig was modified to drill core (without water) at several strategic locations where the overburden had been partly stripped. On reclaiming the cores, all samples were sealed in plastic bags to retain in situ moisture before estimating density. The core samples were then trimmed with a hacksaw to yield regular cylindrical shapes from which volumes could be estimated using the calliper method, and moisture content derived from the 'shavings'. Density values of between 1.72 and 1.84 t/m[superscript]3 were obtained and it was elected to use 1.8 t/m[superscript]3 (112 lbs/cu ft) for estimation of in situ 'wet' bentonite resources.