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Study aims to improve blasting methods

22nd November 2013

By: Carina Borralho

  

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South African mining industry explos-ives supplier BME technical manager Refiloe Kekana has co-written a paper that aims to increase the mining indus-try’s depth of understanding in rock and its characteristics, thereby helping mining companies to plan explosions more efficiently.

“This paper involves designing a blast system using explosives’ energy to break rock,” she says, adding that the main objective of blasting is to fragment rock effectively so that it can be loaded efficiently.

Kekana further notes that undesirable blasting results are expensive to rectify. “Understanding the impact of horizontal structures is becoming essential to blasting operations, since good blasting outcomes have an impact on all downstream activities, such as loading, hauling and crushing.”

The paper, titled Impact of Horizontal Planar Structures on Blasting Results, focuses on near-horizontal dipping structures, found mainly in coalfields where different rock types of varying strengths are blasted simultaneously. “Poor blast outcomes prompted us to investigate what the effect of the structures was on the explosives energy used to fragment rock,” she explains.

Kekana co-authored the paper with BME director of blasting technology Tony Rorke. “We started thinking about writing the paper after we encountered poor blasting results in geological environments of the same type, where a hard sandstone layer would be overlain by a layer of weaker rock such as shale,” she adds.

The paper was initiated in March and com-pleted in July and has since been published for release at the European Federation of Explosives Engineers’ conference, held in September in Moscow, Russia.

The study involved analysing blast videos where differ- ent types of energy transfer could be observed.

“The most common mechanism identified while studying the videos was the transfer of energy from one detonating hole along the plane of weakness that affects unfired charges and down lines in adjacent blastholes,” notes Kekana.

Further, a scenario was modelled to explain the interaction of shockwaves in the different rock types. Currently, numerical modelling is used as a tool to understand the physics involved in blasting and in the transfer of energy. “The real mechanisms are still not fully understood and I believe that also shows a need for further research to fully understand this phenomenon,” she says.

Possible ways of reducing impact would be to use waste decks where the planar weakness is located. This is done by separating two explosives columns in one blast hole with aggregate where the area of weakness is. “Double priming in layered rock has also proved useful. In such cases, if there is any disruption to a portion of the charge, the second booster would be able to recover the detonation up the column,” she adds.

Meanwhile, Kekana shows particular interest in projects involving electronic delay detonators (EDDs). “EDDs provide the flexibility and accuracy that nonelectric detonators – conventional shock tubes – do not have. Drilling and blasting is one of the areas, which, if improved, can have a positive impact on an entire mining operation,” says Kekana.

BME notes that the cost for each EDD unit is slightly higher than that of nonelectric detonators. However, the benefits of having an accurate initiation system justify the cost, as it saves money in the long term.

“Another benefit of using EDDs is the flexibility to use ideal timing delays to ensure that fragmentation is performed properly. Good fragmentation will result in cost savings on the loading and crushing of the material. The downstream cost savings outweigh the marginal cost difference,” says Kekana.

Trends and Technology

BME, which currently focuses on the supply of electronic delay detonators, underground narrow-reef pumping systems and pumpable emulsions, says some mines have only recently introduced EDDs to their operations where controlled blasting is needed.

“In addition to this, at some narrow-reef mines, pumpable emulsions are being trialled. The technology has been available for a few years, but the mining industry has been slow to introduce it to their operations. In areas where they have been implemented, the associated benefits have been realised,” says Kekana.

Future of Explosives

“There are various ways to break rock. However, explosives still remain the least costly way of breaking large amounts of rock in a short time,” says Kekana, adding that, although mechanical rock-breaking technology is becoming available, it cannot be used to break hard rock. Further, the associated costs of the equipment are high.

Kekana is optimistic about explosives in the South African mining industry. “The volumes of explosives used might be reduced in the future, but rock blasting will remain for as long as mining is taking place in South Africa.”

She adds that there is still a need for research on explosive technology in South Africa. “We need to continuously aim to find better ways of making the most of the available energy,” she says.

Meanwhile, Kekana identifies that research coordinator Robbie Robinson’s new method for gold and platinum mining is similar to methods BME uses in opencast mining operations. Robinson says the method, which avoids the wasteful shattering of precious metal during blasting, has the potential to significantly boost gold and platinum mining.

“In opencast mines, where technology, such as EDDs, is implemented, blasts can be timed to separate waste and ore, which reduces dilution,” says Kekana.

She adds that if this method can be success-fully implemented in narrow-reef operations, it would be beneficial to ore recoveries, thereby making mines more profitable.

“With the current economic climate, poor recoveries can mean the difference between profit and loss. It is important to use the technology that is available to us to ensure that we mine smartly and sustainably,” she says.

Further, Kekana believes there is a gap between experienced people and young engineers in the industry who are still learning about explosives. “There is certainly a need for training in the industry.”

Technical Work

Kekana’s technical work in the areas surrounding eMalaheleni and Middelburg, in Mpumalanga, includes drilling and blasting audits, enabling BME to identify any issues that might need correcting and areas of possible improvement.

She also performs blast designs when blasting near structures or in areas where blast-induced vibrations are a concern. “I am also responsible for blast monitoring, when needed, which entails monitoring the performance of BME explosives by measuring the velocity of detonation, using seismographs to monitor ground vibrations, and air blast and shoot high-speed videos to monitor overall blast performance.”

Kekana’s role at BME, where she has been employed since 2009, is changing, to enable her to focus more on research.

Edited by Samantha Herbst
Creamer Media Deputy Editor

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