ABSTRACT: It has long been a goal of blasting to provide enhanced rock fragmentation to improve the productivity of crushing and grinding circuits. Mine-to-mill studies have demonstrated downstream productivity benefits from modest increases in powder factor. However, such increases have been limited by safety and environmental constraints; excessive blast energy usually results in the hazard of flyrock along with other concerns including vibration, airblast or perimeter and wall damage.
Now, a new blasting method has been developed that can overcome these constraints, allowing the use of blast energies that are several times higher than those conventionally used. The method involves dual blast layers within a single blast event that is initiated with electronic blasting systems. An upper blast layer comprising conventional powder factors is initiated first and the broken rock is allowed to fall to rest before initiation of the lower layer which comprises ultra-high powder factors and hence considerably higher blast energy. The broken rock from the earlier-firing upper layer provides an effective buffer to avoid flyrock, enabling powder factors in the range 2–5 kg of explosives per cubic metre of rock to be achieved with control.
This paper presents the concept along with modelling studies and the results of field trials that demonstrate, for the first time, the viability of ultra-high powder factors in open cut metalliferous mining. Independent fragmentation and comminution modelling has also shown that such powder factors can produce much finer rock fragmentation and increase mill throughput by 20–40%. This new method offers the potential to increase mine production and profitability while reducing energy consumption and associated green- house gas emissions.
Source the complete paper from the FragBlast publications: Rock Fragmentation by Blasting – Singh & Sinha (Eds) © 2013 Taylor & Francis Group, London, ISBN 978-0-415-62143-4