Researchers mine Brussels sewers for gold and silver

Summary

A new project sees researchers from three Brussels educational institutions figuring out how to extract precious metals from wastewater residue

Don’t try this at home

Brussels universities VUB and ULB, together with Lucia de Brouckère University College, are working on the project Sublimus to develop an inexpensive and sustainable method for harvesting gold and silver from the sludge collected in Brussels’ sewage treatment plants. Most of this sludge is currently incinerated and sent to a landfill.

In a world where primary raw materials are becoming increasingly scarce,” said project co-ordinator Natacha Brion, “it is crucial to evaluate the recycling potential of existing unused waste streams, such as sludge from treatment plants.”

It is estimated that ore from mines, the traditional sources for metals such as lead, tin, zinc, gold and silver, will be exhausted in about 20 years. The reuse of metals will therefore become increasingly important, as will the search for alternative sources of ore.

Working its way downward

Precious metals such as gold, silver and platinum end up with other heavy metals in sewage via various processes – erosion of gold and silver jewellery, use in medicines and disinfectants and emissions from diesel engines catalysts, to name a few. These metals can be found in the sludge after wastewater is treated.

Sludge has traditionally been used as a fertilizer in agriculture, but because of the high metal concentrations, this practice is now against the law in Flanders. “Large quantities of sludge from wastewater treatment plants show toxic metal concentrations,” says Brion, a researcher in VUB’s Analytical, Environmental and Geo-Chemistry group. “So far, there is almost no other solution than to dispose of it, with the associated costs and environmental risks. Extraction and recycling of metals from sludge would not only address the scarcity of metals, it also makes it possible to turn a toxic waste product into a fully-fledged source of raw materials.”

Researchers will investigate whether they can use special bacteria to ‘wash’ metals from the sludge

For Sublimus, researchers will first study the amount of precious and heavy metals found in the sludge. To do that, VUB researchers are carrying out measurements in sludge samples from the two Brussels treatment plants.

In the next stage, they will investigate how these metals can be extracted from the sludge in an environmentally friendly way. Lucia de Brouckère researchers will investigate whether they can use special bacteria to “wash” metals from the sludge.

Finally, VUB and ULB scientists will explore how they can sustainably purify and recycle the precious metals from this metal mixture. An example is the development of specific gold-binding nanomaterials with magnetic properties that can be removed from the mixture with a magnet after bonding.

The research programme is already underway and will continue until early 2022. It is financed by Innoviris, the Brussels institute for research and innovation.

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