BIG BANG THEORY - JSE MAGAZINE

BIG BANG THEORY

An integral part of mining for generations, blasting is undergoing a transformation thanks to innovative improvements

BIG BANG THEORY

When people think of a mine blasting, they tend to conjure up images of some grizzled prospector of the gold rush days, lighting a dynamite fuse with a cigar or pushing down on an antique plunger. Blasting is popularly seen as a low-tech preliminary to the real mining work, and to some extent this is how it has been treated in the industry.

Reality is different, of course – there have been major advances in blasting technology over recent years, and there are some intriguing prospects on the horizon. At a time when mining houses are doing everything possible to reduce costs and increase productivity while trying to improve workplace safety, new blasting technologies can potentially make a big difference to their success.

As the Rand Corporation think tank noted in a report years ago, many companies have neglected blasting in favour of innovations at later stages of the mining process. Their choice of blasting methods has often been determined by the cost of materials. The proportion of costs comprised by drilling and blasting varies greatly depending on the mineralisation, overburden and mine plan of any particular operation. It can range between 8–30% of overall operational expenditure.

Good blasting can have a decisive effect on the efficiency of other downstream operations at a mine as a low-energy means of breaking rock ores into fine particles that are easier to process. The Australia-based Orica Mining Services estimates that blasting comprises only 2% of a mine’s energy needs, compared to 53% for the mechanical crushing and grinding stages. Effective blasting with a good ‘powder factor’ – the capacity to pulverise rock for a given volume of explosive – can deliver a 23% reduction in energy use and a 28% increase in throughput at a grinding mill.

Over the past three decades there has been a move towards subcontracting blasting services. Many equipment and explosives manufacturers have repositioned themselves as service providers.

Companies such as Orica charge mine operators per blast to deliver ore that has been broken down to a specific particle size. But the powder factor is only one of many that drive innovation in blasting technologies. Some innovations are focused on the explosive itself, for example, its stability when transported and used, the way a particular explosive detonates and its noise levels.

Others stem from the delivery system – whether the explosive comes in discrete cartridges or if it can be delivered in bulk as a gel or emulsion. Current research looks at the overall blasting system – how to lay out charges to ensure the best result for a certain area, or how to carry out complex blast patterns remotely, reducing the risk to mineworkers.

It’s impossible to write a comprehensive survey of new blasting technologies in one short article, but a few recent developments are particularly interesting. On the explosives front, some experts have been looking at a new compound, nickel hydrazine nitrate, (NHN) as an alternative to lead azide and similar compounds used in detonators – intended to set off larger charges of bulk explosive.

NHN can be prepared at low cost with fewer environmental impacts. It is also less likely to detonate unexpectedly when subjected to friction, static electricity or physical impacts. Detonations have also been improved by the transition to shock tube technology, a relatively late arrival in SA. The latest shock tube innovations – for example the regionally produced Master Blaster clip system – allow charges to be detonated with no explosives ‘out-of-hole’ and exposed to workers.

When it comes to large-scale blasting over complex below-ground formations, a promising recent development has come from a company with a long history of blasting, Dyno Nobel, which held Alfred Nobel’s original patent for dynamite.

The company has successfully demonstrated its Differential Energy blasting method, which allows individual drill holes to be charged with a bulk explosive that varies in blast energy along the length of the hole. This means the explosion’s power is concentrated in the optimum location. Recent tests at a US gold mine suggested using this method increased shovel productivity by around 8%, while improving the powder factor and reducing emissions of nitrogen oxides.

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‘Some mine operators insist on the latest best technology, others talk safety but don’t implement’

MARTIN PLICHTA, BLASTING EXPERT, AEC ELECTRONICS

Another development attracting attention in the industry has been the introduction of blast movement monitoring (BMM), led by Australia’s Blast Movement Technologies. The company produces hard-wearing sensors that can be placed in drill holes adjacent to explosive charges, recording the subtle displacements of ore that follow detonation. This means that mines can avoid diluting ore with waste rock as they shovel blasted material, or conversely, avoid sending ore to tailings dumps in error – reducing costs or improving profits in either case.

At a higher analytical level, some firms have developed computational models that finely tailor blasting methods to particular mines. British consultancy Blue Dog Scientific has based its business on modelling ‘non-ideal’ blasting situations, which differ from the theoretical conditions on which many plans are formulated. This allows the company to tailor its advice for specific rock conditions, hole diameters and other variables. Blue Dog recently signed a collaboration agreement with local blasting firm BME Mining.

Blasting expert Martin Plichta of AEC Electronics (AECE) speaks about the situation in SA. AECE makes a wide range of equipment for local and international use, including its Magnastart system for centralised blasting. It has become a key feature of SA’s mining landscape after government started pressuring companies to ensure safer working conditions.

He says the local uptake of innovative blasting methods has been somewhat mixed. ‘There is some divergence and almost schizophrenia regarding technology in SA. Some mine operators insist on the latest best technology, others talk safety but don’t implement. In general there seems to be more resistance to change than early adoptions. Typically a five-year lag is seen.’ He says costs remain a central factor in any choice of method.

‘Most mines will not look at new technology unless it is cheaper than what they are currently using. The cost factor depends on the project. In quite a few instances the cost differential between the new technology and the old is small, and the benefits of the new technology actually pays the mine to convert,’ he says.

‘SA mines are under huge pressure economically at the moment. Labour costs have skyrocketed and productivity has stagnated or declined. Simpler, easier ways to mine are being looked into. Optimisation of supplier cost seems to have reached its end, so alternatives and sometimes old solutions are being re-examined.’

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There are many potential blasting technologies to choose from, and further developments are in the pipeline. Some of these include a move away from the widespread use of high explosives towards slower ‘deflagration’ compounds, which do not detonate but develop an explosive pressure through burning like fireworks. These produce less seismic disturbance and gas emissions than conventional explosives, while generating a powerful ‘heaving’ effect that excels at breaking rocks. They may also serve well in the emerging field of seabed mining, where high-explosive shock waves can be particularly damaging to marine life.

Further ahead, blasting may no longer be needed for some applications. In recent months a great deal of attention has been paid to announcements from AngloGold Ashanti. The company has pioneered a blast-free mining method at its TauTona gold operations west of Johannesburg. It has developed reef-boring machines that cut rock without explosives, using these to dig out and then backfill the high-grade support pillars that have remained on older levels of the mine, and which could not be extracted with explosives for fear of collapse.

AngloGold spent more than $30 million developing the technology and CEO Srinivasan Venkatakrishnan has said the move could add 30 million additional gold ounces to the company’s SA reserve base.

Companies prepared to look at recent innovations may find that there are savings to be made with environmental and safety improvements.

By David Bannister
Image: Andreas Eiselen/HSMimages