A British scientist has found a use for waste glass that cannot be recycled to help clean polluted waterways by acting as a filter to remove toxic metals.

Currently, only a small amount of waste glass bottles and jars can be recycled, partly because much of the glass is coloured brown or green, and partly because the market sustains only a limited weight of recyclable glass.

Millions of tonnes of waste container glass are generated across Europe. As such, large amounts of this waste, purportedly for recycling, are shipped to China and elsewhere to be ground up and used as hardcore filling materials for road building.

But now, Dr Nichola Coleman, of the University of Greenwich, London, has developed a simple processing method for converting waste container glass - called cullet - into the mineral tobermorite.

Dr Coleman, a senior lecturer in materials chemistry at the university's Medway campus, said: "The novelty of the research is that the glass can be recycled into something useful - nobody has previously thought to use waste glass in this way."

The research has found a potentially valuable new use for the large quantities of coloured glass that are being stockpiled in the United Kingdom and in Europe, because there is less recycling demand for green and brown bottles than there is for clear bottles.

Dr Coleman's simple processing system creates tobermorite, a naturally occurring mineral, by combining waste glass with other basic materials.

A mixture of ground glass, lime and caustic soda is heated to 100 degrees Celsius in a sealed stainless-steel container to produce tobermorite. The mineral, which can be produced as a powder or granules, can be used to absorb toxic heavy metals from water located beneath the ground or waste water streams.

Tobermorite is hydrated calcium silicate, with silicate being the main material that can be extracted from glass. In the form produced - the phase-pure 11-angstrom form - the mineral can be used as an ion-exchange material that can extract toxic lead and cadmium ions from industrial effluent, waste water streams or contaminated groundwater.

To make tobermorite, Dr Coleman heats a mixture of ground cullet, lime (as a calcium source) and caustic soda (sodium hydroxide solution) to 100 C in a sealed Teflon container.

Initial tests show that the uptake of lead and cadmium from solution is rather slow, therefore Dr Coleman suggests that, at this stage of development, the synthetic mineral might best be used in the in-situ remediation of groundwater rather than in industrial ex-situ effluent filtration processes. The concept is now being extended to create other classes of ion-exchange filter from non-recyclable and low-quality waste glass.

"The cullet-derived sorbent could be used in reactive barriers to prevent the lateral migration of pollutants in groundwater, rather than as a remediation material for waterways," added Dr Coleman.

"Heavy metal-contaminated land and groundwater are global problems, arising from industrial and military activities and also from the natural leaching of heavy metal-bearing minerals," she said.

Dr Coleman is now looking at creating other types of filter and forming barriers that could prevent pollutants spreading from contaminated areas.

Details of the research have been published in the International Journal of Environment and Waste Management.