Unrecyclable waste glass converted to mineral can be used to extract contaminants
A materials chemist from the University of Greenwich, London, has developed a way of using unrecyclable waste glass as a filter that could help clean up polluted waterways. The details of the science are published in a forthcoming issue of the International Journal of Environment and Waste Management.
Only a fraction of waste glass can be recycled, partly because much of the glass is colored and partly because the market sustains only a limited weight of recyclable glass. Millions of tons of waste container glass generated across Europe often are shipped to China and elsewhere to be ground up and used as hardcore filling materials for road building.
The scientist, Nichola Coleman, developed a simple processing method for converting waste container glass, or cullet, into tobermorite. The mineral is hydrated calcium silicate, 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, wastewater streams or contaminated groundwater.
To make the tobermorite, Coleman heated 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 showed that uptake of lead and cadmium from solution were slow, so 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 unrecyclable 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,” said 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.”