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A Fragmentation Model to Estimate ROM Size Distribution of Soft Rock Types

Authors:  D.M. Thornton, Julius Kruttschnitt Mineral Research Center (JKMRC)
                S.S. Kanchibotla, DynoConsult - Dyno Nobel Asia Pacific Ltd.
                J.S. Esterle, CSIRO, Exploration and Mining

Abstract:

Fragmentation modeling in soft rocks presents a challenge due to their propensity to further fragment after blasting during normal handling.  Coal and some iron ore deposits are examples of materials that undergo significant degradation during the extraction, hauling and dumping process of the mining operation.

The Kuz-Ram model is an empirically derived predictor of size distribution from blasting hard rock.  Little breakage occurs during excavation and subsequent sizing of hard rock, so the measured Run of Mine (ROM) size distribution is essentially the same as the post-blast (before excavation) size distribution.  However, for soft rocks, each step of the excavation and hauling operation imparts energy to the rock particles so the measured ROM size distribution will be significantly different from the post-blast size distribution.  In order to calculate the ROM fragmentation at any stage of the extraction (or sizing) operation, the JKMRC has developed a model that combines both blast fragmentation and degradation through subsequent handling.

The blast fragmentation is calculated with a modified version of the Kuz-Ram model that improves the prediction of the fine portion of the product.  The degradation module is an energy-based size reduction process that is particle size dependent, taking into account the conditioning that occurs during cumulative damage.  Modeled size distributions have been compared with full-scale sieved ROM size distributions with very good agreement.
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