Getting precious metals from dry slag

A modern facility in the Zurich Oberland that sorts precious metals from dry slag has turned out to be a veritable gold mine, with some of its finds yielding millions of francs. It's a great example of how valuable raw materials can be recovered from waste. (SRF/swissinfo.ch)

Around 300 tonnes of dry slag are delivered daily by truck and train to the KEZO plant in Hinwil. The material has already passed through the ovens of other incineration plants and contains precious metals. From the container, the slag goes to a modern sorting machine,which works at low pressure and is airtight so that no dust is produced. The dry slag is sent through a labyrinth of pipes, conveyor belts and sieves. The machine shakes, jiggles and blows the metal parts – brass, iron, gold, silver and copper – separating them into different sizes. 

The metal granulate is then sent to Germany, Sweden and Belgium, where incinerators turn the metals into pure copper, silver, aluminium and gold. In 2017 the plant in Hinwil yielded 65kg of gold worth CHF2.1 million ($2.3 million), and 1,750kg of silver worth CHF800,000. The revenue covers the operating and capital costs of the sorting machine.