FEATURED TOPIC — GLASS RECYCLING
Glass waste to toothpaste UNIVERSITY OF QUEENSLAND RESEARCHERS HAVE DEVELOPED A NEW CHEMICAL PROCESS THAT CAN TURN WASTE GLASS INTO VALUABLE SILICATE PRODUCTS.
Rhys Pirie and his colleague are using a chemical processing method to produce sodium silicate from glass fines.
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lass fines have historically been perceived as a low-grade product. According to the Glass Packaging Working Group 2018, improved technology allows for increasing amounts of glass fines to be mechanically recovered. However, limited markets for the large volumes of recovered glass which does not meet the quality specifications for glass manufacture has resulted in material being stockpiled. Researchers at the University of Queensland recently announced they had developed a process that provides glass fines with a high value end market which does not require access to optically sorted cullet streams. With funding from the Cotton
28 / WMR / May 2019
Research and Development Corporation and the Federal Government’s Department of Agriculture and Water Resources, PhD candidate Rhys Pirie and Professor Damien Batsone are using a chemical processing method to produce sodium silicate from glass fines, sidestepping sorting issues and providing significant environmental and economic benefits. Sodium silicate can be used to manufacture thousands of commodities, from concrete sealers and rubber to toothpaste and detergent, with major end markets being health care, mining, catalysts and silica gel. Silica gel is a desiccant, meaning it absorbs and holds water vapour. It is the active ingredient in the “do not eat” packet found inside shoe boxes,
biscuit packaging, vitamin bottles and a range of other household products that require dry atmospheres. Rhys estimates the global market for sodium silicate is valued at around $10 billon, or eight million tonnes. When Rhys and Damien first started working together in October 2017, they were hoping to find a low-cost source of silicon for agricultural fertiliser amendments. They then began to explore different ways to make the silica in glass more available for plant uptake, before realising one of the chemicals they were producing was sodium silicate. After researching the chemical, the pair noticed a large difference in relative value between silicate and glass fines, suggesting a significant reuse market was being underutilised. The Department of Environment and Energy’s 2018 National Waste Report shows alternative markets for recycled glass in Australia were undeveloped, which highlights a significant opportunity for expansion. According to Rhys, fines from waste glass have a value of approximately $10 per tonne when used in roadbase while sodium silicate has a value of less than $1000 per tonne. Rhys and Damien chemically recycle waste glass by digesting it in an alkaline solution. The reaction products are then processed, with the end result being sodium silicate and silica gel.
