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Stability of re-pumpable emulsion cuts underground costs

The Megapump range of double-salt emulsions from BME is so stable that it can be pumped and re-pumped multiple times, opening the door to a variety of cost-saving opportunities for underground mines.

“We can confidently say that our emulsion is the most stable on the SA market,” said Selwyn Pearton, Research and Development manager at BME, “containing an ammonium nitrate and calcium nitrate mix that delivers remarkable qualities, even compared to other double-salt emulsions on the market.”

In addition to its resilience to multiple pumping cycles, it also has a very long shelf-life, said Pearton, having been successfully used for blasting up to a year after being manufactured.

“The ability to re-pump the product has huge benefits for an underground operation,” he said. “Essentially, it allows a mine to pump emulsion from the surface to the underground workings safely, quickly and cheaply, avoiding much of the disruption and expense associated with normal explosives.”

For a start, the emulsion is regarded as a 5.1 oxidiser in terms of the United Nations transport classifications, allowing it to be transported without the stringent requirements applied to other explosives. It is only sensitised in-situ in the blasthole at the workface, when the blast is about to take place.

This means that the usual safety precautions and time constraints associated with moving explosives underground including dedicated shaft and locomotive cycles can be avoided. There are also considerable savings in labour as emulsion can be pumped between cassettes and through the shaft system simplifying the transportation cycle on the way to the blastface.

BME has also engineered a bag or cassette-based charging system through which workers can transport emulsion through the demanding confines of narrow-stope mines, before being loaded into blastholes quickly and efficiently.

BME

While it is much safer and simpler to transport any emulsion rather than an explosive, the limitation of less stable emulsions is that they can’t stand up to the number of pumping cycles ideally required to get it from a surface location to the stopes, said Pearton.

In a typical chain of events, the emulsion is first pumped into the silo at the manufacturing facility before being gravity-fed into the tankers that supply the mine. At the mine the emulsion is pumped into a silo before being pumped through multiple transfer cassettes or pipelines before entering the charging unit that will again pump the emulsion into the blastholes to charge them.

Applications vary between mechanised operations where the excavation is large enough for a mechanised charging unit, and a narrow reef environment that requires workers to take the emulsion into the stope for blasting. The latter can take advantage of BME’s closed emulsion system, where the product is pumped into small, sealed bags which are cycled into the confined spaces where blasting takes place before being returned for refilling. The design of the system ensures that there is no contamination of the emulsion, which could damage equipment and affect the results of the blast.

“It is a significant drawback to alternative systems that they cannot pump emulsion into small bags due to the risk of crystallisation – caused by a breakdown of the emulsion matrix,” said Pearton. “Most other emulsions on the SA market can only be re-pumped about three times before they start to breakdown.”

The stability of the BME product also allows it to stand for a very long time – both before and after it is sensitised – and still deliver the high detonation qualities for which emulsions are well known.

“The longest that we’ve had our emulsion stand is a whole year,” he said. “The mine actually closed for a period, and then re-opened and continued to mine with the product that we had initially supplied a full year earlier. That is unheard of in SA, and it’s only possible because of Megapump’s remarkable stability.”

Once the product has been charged into the blast-face, it has also demonstrated its longevity. An opencast client, for instance, had blastholes charged six months before they were finally detonated, with no detrimental impacts on the quality of the blast.

“In the underground environment, we have had experience of blasting a panel two weeks after the blastholes were charged,” said Pearton. “Once again, the results were perfectly satisfactory. So the client is not pressurised to blast within a certain time limit after the emulsion is sensitised.”

He noted that the Megapump range of pumpable emulsions range from emulsions designed for use in large diameter vertical blastholes to 8D cap sensitive formulations for the narrow reef environment. . “This diversity in our emulsions means that the blasting cycle can be optimised. An example of this is our Megapump - Narrow Reef formulation that does not require the use of a booster in the initiation process, so that means less cost for the operation and a simpler and faster loading procedure,” he said.