The clays removed 90-98 per cent of copper from a 20ppm solution, even at slurry concentrations below 1 per cent dry weight of clay. Another useful property of the clays was their ability to neutralise the acidic copper solution, even at low clay concentrations.

The glauconitic sand also showed considerable potential to remove copper, especially at slightly higher concentrations where 98 per cent removal was routinely recorded. The glauconitic sand from a marine deposit offshore from Namibia was included for comparative purposes.

If commercially exploited it could be used in packed columns.

The results indicate that a beneficial use could be found for many clean dredged clays.

Phil Smith of Aquatonics said: 'In future dredged clays, especially those from capital dredging, could be an important method of controlling metal pollution and cleaning up rivers and streams affected by historic mining activities.'

"We are actively seeking collaboration from ports, dredging companies, mining, metalliferous industries and effluent treatment companies to pursue the commercial exploitation of this research. Field trials have shown that in-stream treatment of polluted streams is practical, which would greatly reduce the costs of cleaning up areas contaminated by mining activities, " said Smith.

The main findings from this study and previous reports are available from Phil Smith at Aquatonics Ltd, email earth@online.rednet.co.uk.