Gravity-Driven Treatment of Mine Water Slashes Energy Use

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Tuesday, December 3rd, 2013
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A new gravity-powered process for the treatment of polluted mine water can achieve energy savings of at least 50 per cent compared to its conventional peers.

Water pollution is one of the core environmental impacts of mining operations, requiring significant expenditure to remedy in the form of large and costly on-site treatment facilities.

The water used in the mining process is readily contaminated by heavy metals, while the oxidation of metal sulfides contained by the ore body can rapidly cause acidity following exposure to the air.

A new method devised by engineers in Britain called NeutraSeal could radically reduce the cost of treatment of mine water by taking advantage of basic principles of fluid dynamics which have been observed since antiquity.

The process uses the downhill flow of contaminated water in a mine to produce a hydraulic head which powers its subsequent motion.

This hydraulic head serves to drive the mine water into a sealed chemical treatment plant, dispensing with the need for a conventional pump which can consume large amounts of energy.

A siphoning effect is achieved by discharging the water from a lower exit point, thus enabling the system to operate at a position which is situated higher than the mine itself.

A key challenge for this process was increasing the amount of dissolved oxygen in the water without creating gas bubbles, which would stymie its movement in the siphon.

Justin Daglish, Minus Engineering director

Justin Daglish, Minus Engineering director

Justin Daglish, director with Minus Engineering, the company responsible for developing the system in conjunction with Exeter University, said this was achieved via the installation of a junction tank in tandem with the use of an electric pump to control inflows and outflows of water.

Water first passes through the junction tank prior to entering the plant, where it is dosed with lime to lifts its pH to a neutral level, thus curing it of its acidity.

The water then flows into an aeration tank, which increases its oxygen levels, before circulating back into the junction tank.

While the flow of the water is powered chiefly by the hydraulic head, an electric pump is used to strictly control the flow volume, ensuring that the amount which enters and exits the junction tanks is always on par, thus preventing aeration.

In the final stage of the process, the water is sent from the junction tank through a tilted plate separator which extracts any precipitated metals. The water is then ready for external discharge.

According to its developers, the system only needs to be 60 per cent the scale of its conventional peers, costing approximately 30 per cent less to construct.

A pilot plant has already been built which is capable of siphoning liquid to a height of 10 metres and treating three cubic metres of water in an hour.

Daglish said this prototype achieves a 50 per cent energy saving compared to its conventional peers. This saving should also be subject to economies of scale and will increase with the size of the plant as a result of the reduction in frictional losses achieved with enlarged pipe sizes.

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