Tackling nitrate contamination of water in mines
- Published: Friday, 15 December 2017 15:04
In South Africa’s increasingly water-scarce and environmentally regulated mining industry, BME’s emulsion explosives help keep nitrates out of mine water – preventing possible groundwater contamination and allowing optimal recycling of water on site.
“Recent international studies suggest that up to 28% of nitrates1 from traditional ammonium nitrate fuel oil (ANFO) explosive can leach into water draining through underground mine workings during a blasting campaign,” said BME operations manager Neil Alberts. “These levels can be reduced to as little as 2% by applying best practice, but the long-term solution lies in explosives that do not release nitrates into water sources.”
As the pioneer in cold emulsion explosives in South Africa, BME has evolved this technology to new levels over the past three decades, said Alberts.
“Among the characteristics of our emulsions range is its excellent water resistance, which means that the explosive material does not dissolve readily in water,” he said. “This reduces the amount of nitrate leaching to negligible levels.”
Tests conducted by BME indicated that, after being immersed in water for a month, its emulsion released only about 0,7% of its nitrate content.
“The key factor here is the effectiveness with which the oil in the emulsion – the fuel phase of the mixture – surrounds and isolates the small droplets of saturated oxidizer salt, preventing them from dissolving in water,” said Alberts. “On the other hand, our tests confirmed that ANFO dissolves completely when it comes into contact with water.”
High levels of wastage of ANFO – the mining sector typically accepts that about 30% of ANFO delivered to a blast site is not consumed in blasting – suggest that it may be a contributor to nitrate levels in water passing through mine workings.
Another advantage of emulsions highlighted by the tests was that no oil was released, ensuring that water contamination by oil is also prevented; both the nitrate and the fuel phases of the mixture are bonded tightly by the emulsifier.
“BME emulsions have already contributed to environmental sustainability on mines by incorporating and consuming previously used oil in its emulsion products, helping mines to dispose of these liquids safely and cost-effectively,” he said. “The way we have evolved the matrix also ensures that no oil is released when our emulsion comes into contact with water at the stope face.”
As mines work to prevent or mitigate environmental damage, pollution or ecological degradation, the levels of nitrate in water are usually monitored – as high nitrate levels can render water unsafe for drinking.
“By removing the possibility of nitrate leaching from blasting chemicals underground, mines can reduce the risk of groundwater contamination as water drains out of working areas,” said Alberts. “At the same time, where mines are making efforts to recycle water from underground, lower nitrate levels will enhance the overall quality of recycled water and increase its applications on and off the mine site.”
Emulsion explosive is part of a growing range of underground services being innovated by BME, including up-hole blasting technology, vertical pipelines to convey emulsion direct from surface to working levels, mobile chargers and pumps, and control systems to facilitate real-time communication between underground operations and surface systems.
1 http://mdag.com/MDAG%20Paper%20Database/M0069%20-%20Morin%20and%20Hutt%202009%20-%20Nitrogen%20Species.pdf – see page 5, 3rd-last paragraph