Many of the Earth’s natural elements including copper, cadmium and iron are suffering from depletion of their primary sources, yet there is rising demand for them due to population growth and increases in the standard of living. Fifty per cent of the world’s primary mined iron and copper is now unusable because it has been landfilled or dumped in different waste streams. For the sustainability of these natural resources, societies need to act.
We should shift from the current linear economy model (where natural resources are taken, goods are made, consumed and finally dumped in landfills) into an enhanced circular economy model (repair, reuse and recycle plus extraction and recovery) by including the ‘lost’ materials in landfills and old open dumps as secondary resources.
Landfills and dumps, even the ones with hazardous wastes, should be regarded as ‘banks’ of secondary resources for our future needs instead of being ‘forgotten graves’. We can recover these waste materials by mining old and still active landfills and dumpsites in just the same way as we mine ordinary mines.
In Sweden and other European crystal glass producer countries such as Italy, waste glass represents a real problem. At former glasswork sites, contamination is found in the soil and in waste, with hazardous concentrations of elements such as lead, cadmium, arsenic and others. My research focused on finding a method to extract these elements, instead of dumping the waste glass and contaminated soil in landfills, as suggested by government environmental protection agencies.
The reduction-melting method, which I developed, is based on the fact that metals have a greater weight than glass. Mixing the glass – which usually contained more than 30% lead by weight as lead oxide – with chemicals can lower the melting temperature of glass and liberate these oxides.
I tested different chemicals and found that carbon could be an effective agent to reduce metal oxides inside the glass structure to produce metals. These metals are gathered and precipitated down in the molten mixture, leaving the glass clean. After two hours of melting at 1,100°C, about 99% of lead, cadmium and arsenic could be extracted. The purity of the extracted lead was high, at about 90%.
During my investigation, I also studied the performance of chemical extraction by chelating agents to extract lead, cadmium and arsenic from a mixture of soil and glass with particle sizes of less than 2mm. I found that less than 41% of metals could be extracted due to the challenging composition of this mixture. But the method could be developed further because my trials were done at room temperature and with neutral pH values which could affect the extraction of metals from this mixture.
The reduction-melting method could be used to extract lead from all kinds of leaded glass, including cathode ray tube (CRT) glass from old TVs, computer monitors and so on. If we consider the amount of this type of waste on a worldwide basis, we can imagine the extent of resources that we could gain from this waste.
Around 9.5 million tonnes of waste electrical and electronic equipment (WEEE) was generated in the EU in 2012, while 43 million tonnes of old CRT TVs and monitors was generated in China in 2013. These numbers are set to increase, especially with the current development of flat panel technology for video display that will lead to the widespread replacement of TVs and monitors.
As a rough estimate, each one of these units contain 0.5-1kg of lead and other metals. Using the reduction-melting technique would recycle millions of tonnes of lead and other metals back into the circular economy instead of the materials being considered a burden to the environment and human health.
I see this method as having the potential to overcome the environmental and health hazards of metals contained in WEEE glass waste. But it is still currently at laboratory scale and needs to be further developed into a pilot or full-scale plant. I hope that with co-operation between academia, the business sector and decision makers, the method will be developed into an industrial plant for extracting and recycling metals from WEEE glass.
Yahya Jani is a doctor of environmental science and chemical engineering in the department of biology and environmental science at Linnaeus University in Sweden