Incinerator bottom ash has gold rush potential

Energy-from-waste companies are sitting on a lucrative "gold mine" of valuable metals in incinerator bottom ash which they could profit from if these materials were recovered.

Fred Sigg, head of research & development at Hitachi Zosen Nova – a leading waste-to-energy technology provider – said that the ash had “tremendous value” due to the small amounts of valuable and rare earth metals such as copper, gold and silver contained within it.

However in order to recover these metals, many plants would have to retrofit a different type of ash extraction system, he maintained.

“Most plants use a wet bottom ash extraction system … we need to change that to a dry process, one which has no contact with water,” he said.

This, Sigg explained, would result in the production of a crumbly ash that is easy to separate and that avoids any corrosion of the metals. The ash could then be further refined into three different fractions – the finest of which would contain valuable particles of these materials.

He pointed to a pilot process in Switzerland using this system, attached to two energy-from-waste plants. It is generating bottom ash compositions of typically 11% iron, 2.2% aluminium, 0.5% copper and 0.003% gold.

“That amount of gold may not seem a lot, but multiply that by the price of gold and it becomes significant,” Sigg maintained.

Removing the metals and copper in particular from the ash also improves its leachability and effectively moves metals recovery up the waste hierarchy, he added.

Sigg was speaking earlier today at the Resource & Waste Management show in Birmingham.

Maxine Perella

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