Dr Nichola Coleman and colleagues at Greenwich University began the project as a way of finding a use for the large quantities of stockpiled coloured glass, which is in less demand for recycling than clear glass.
In a process known as hydrothermal synthesis, a mixture of this ground glass along with lime and caustic soda is heated to 100˚C in a sealed stainless steel container to create the mineral tobermorite.
Although naturally occurring, tobermorite is very rare and is therefore not extracted commercially by mining companies. Nevertheless, it does have some interesting and useful properties. As a silicate hydrate cation exchanger, tobermorite can absorb and incorporate toxic heavy metals to form a relatively inert complex.
As such it could potentially be deployed as powder or granules to contaminated wastewater streams or water located beneath the ground.
‘The current standard procedures for the remediation of heavy-metal-contaminated land are to “dig and dump” through excavation and landfill, or to encapsulate the site in concrete,’ Coleman told The Engineer.
Her team is now looking at creating other types of filter and forming barriers that could prevent pollutants spreading from contaminated areas.
‘Further research will be required to establish the geo-engineering aspects of any barrier system incorporating the tobermorite — I guess it would involve a trench lined with a geomembrane filled with a mixture of tobermorite and aggregate to optimise porosity.
‘The barrier could remain in situ or be excavated, depending on the subsequent use of the land.’
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