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MEI Online: Environmental Issues: Latest News: October 10th 2002


:: First large-scale PRB for UK  

Northumberland County Council and the University of Newcastle upon Tyne are working together to solve environmental problems caused by the seepage contaminated water from a spoil heap on the site of the former Shilbottle coal mine. The site had already been cleared and restored. However, the three-artificial reed beds which were constructed to treat surface run-off from the spoil heap prior to release of the water into a local river were proving ineffective.

An assessment found that the reed-beds were proving ineffective for two reasons. First, the reed-beds are an aerobic system, which results in a fall in pH as iron is precipitated, which in turn limits the precipitation of iron. The assessment found that an anaerobic system would be more effective, as acidity is removed allowing more iron to be precipitated. The second reason for the lack of success in preventing pollution of the nearby river was that the bulk of the most highly polluting water was seeping from the heap directly into the river bed.

In an attempt to overcome these failings, the council and University of Newcastle have designed a passive treatment system comprising a permeable reactive barrier (PRB). The barrier will involve the construction of a trench some 2 m wide and 2-3 m deep. The trench, which has been 'keyed' into an underlying clay horizon, will be filled with a mixture comprising 50% calcite limestone chips with an average diameter of 20 mm, 25% 'green waste' compost and 25% manure from mammalian herbivores (most likely horses). The designers believe that the mixture will promote the generation of sulphate-reducing bacteria. These promote a variety of biochemical reactions which 'consume' acidity and 'generate' alkalinity, which in turn encourages the precipitation of iron and other metal contaminants within the PRB as metallic sulphides.



Click for more info on Hi-Tech Metals '18

Paul L. Younger
Newcastle University
Tel: +44 (0)191222 7942
Fax: 222 6669

Mining Journal, Sept.27, 2002, p.216

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