Case of study on particle shape and friction angle on tailings

Abstract

Tailings are crushed and milled materials result of the mining production. Tailings need to be stored in facilities, usually tailings dams, for a long time period for mainly safety and environmental protection. In order to design tailings dams in a long term perspective not only current material properties is needed but also future changes of these properties due to e.g. weathering. On a particle level the weathering will result in shape changes and decomposition. By studying the changes in shape a prognosis of changes in properties of a tailings deposit may be established.
Tailings are site specific material and are not well investigated compared to natural geological materials such as soil. Tailings materials size ranges generaly from sand to silt and the particle shape by genesis or production processes. Based on laboratory tests tailings from the Aitik mine has been investigated through triaxial tests and particle shape quantification by two dimensions image analysis. The shape descriptors Aspect Ratio, Circularity, Roundness and Solidity are used in this study. These shape descriptors are evaluated based on how well these describes talings materials. The evaluated shape descriptors are used in previous published empirical relations between shape and friction angle. As reference are friction angles evaluated by triaxial tests on the material used.
The results show that the particle shape is affected by the size of the aggregates. Aggregates in small fractions are more elongated and less rounded, i. e. more angular, compared to larger. Furthermore, the Aspect Ratio and Circularity seems to be the most situable quantities to describe the tailings behaviour in relation with the empirical model. The accuracy in predicting the friction angle of the tailings by previously published relations based on uniformly graded sand material are low. But the systematic underestimation of the friction angle indicates that it would be possible to establish such empirical relations based on tailings material.