Waste glass to clean water
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 quantity of recyclable glass.
Millions of tonnes of waste container glass are generated across Europe alone. As such, large amounts of this waste, purportedly for recycling, are shipped to China and elsewhere to be ground and used as hard-core filling materials for road building. But now, Nicholas Coleman of the University of Greenwich, London, has developed a simple processing method for converting waste container glass, called cullet, into the mineral tobermorite.
Coleman, a senior lecturer in materials chemistry at Greenwich University, said, “The glass can be recycled into something useful. Nobody has previously thought of using 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. 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 make tobermorite. The mineral, which can be produced as a powder or granule, 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 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 ground water.
Geetha Balachandran
