ATTRITION OF HYDRARGILLITE (AL(OH)3) - MECHANISM AND QUANTIFICATION OF PARTICLE FRAGILITY BY A NEW ATTRITION INDEX

International standards and specifications require that the alumina particles obtained by calcination of hydrargillite aggregates are large enough to avoid breakage and dustiness during mechanical carrying and handling. The particle fragility is generally estimated by an attrition index obtained by comparing the initial and final sizes of particles undergoing an attrition test. In the present work we modify this test and apply it to samples of hydrargillite aggregates from different origins, with different internal structures and particle size distributions. It is shown that the commonly used attrition index is affected by size distribution and attrition mechanism. In addition, it does not really describe the particle fragility. Therefore, we propose a real fragility index named F30 which is not only independent of the particle size but also gives some information on the attrition mechanism. If F30 < 20, hydrargillite is strong and attrition occurs by abrasion. If F30 > 20, hydrargillite is weak and attrition occurs more by breakage of the aggregates than by abrasion.