Cleaning up polluted minewater could become far less energy intensive thanks to a new gravity-powered treatment system.
A team of British engineers have developed a system for neutralising acidic mine-water and cleaning it of heavy metals, which they claim uses at least 50 per cent less energy than conventional pumped systems.
The technology, known as NeutraSeal, uses the hydraulic head created by the downhill flow of water from the mine to a lower body to drive water through a sealed chemical treatment plant, which the engineers say would typically be 60 per cent the size of conventional facilities and cost around 30 per cent less to build.
Sealing the system, developed by UK firm Minus Engineering and Exeter University, enables it to use a siphoning effect and so operate at a location that is higher than the mine as long as the water exits to a lower point.
The principal innovation was finding a way to increase the dissolved oxygen content of the water while removing bubbles of gas that could halt the flow of water in the siphon, said Minus Engineering director Justin Daglish.
‘If you have bubbles in the line then the siphon won’t work,’ he told The Engineer. ‘You could just use it under gravity-flow conditions but using siphon conditions allows you to keep your plant dry where the plant is higher than the mine.’
Water enters the plant via a junction tank and is then dosed with lime to raise its pH to neutral. The water then arrives at an aeration tank, where its oxygen content is increased, before it is returned to the junction. The flow is driven primarily by the hydraulic head but controlled by an electric pump.
‘The water out of and into the junction tank is controlled so the flow is always equal, which means the aeration is not happening within the siphon,’ said Daglish.
The water then leaves the junction again via a different route and its precipitated metals are removed with a tilted plate separator. The water can then be returned to the environment.
The research team has built a pilot plant using a £100,000 grant from the Technology Strategy Board (TSB) that has a footprint similar to two shipping containers and that can treat 3m3 of water a hour, siphoning up to a height of 10m.
‘We had 4m of head on our pilot plant operating under siphon conditions and we got about a 50 per cent energy saving on what they do currently,’ said Daglish. ‘And the energy savings will go up with scale because the frictional losses will go down: the bigger the pipes, the less the friction.’
The company is now looking for a partner to help scale up the technology for markets in South Africa, where the mining industry has been hit by energy restrictions in recent years, South America and possibly the US.