'There's gold in them thar sewers'

3 December 2015

Researchers from Cardiff University have discovered “consistently high” levels of gold in Britain’s sewer systems that could yield £13.6 million a year.

A team at the university’s School of Earth and Ocean Sciences led by Dr Hazel Prichard working with Thames Water has found the gold in leftover solids from wastewater treatment, also known as sludge.

Her team estimated that incinerated sewage ash is made up of between one part and seven parts per million of gold, which would make it economically worthwhile to extract the gold.

Dr Prichard said she was not sure exactly how the metal got into the sewer system but that it could have been washed off pavements in areas where people walk wearing jewellery.

It was also possible that people washing up could rub off bits of gold from jewellery, which could eventually end up in the drains.

The research is in early stages and the team are now analysing the most effective methods to extract the gold.

“That’s the million dollar question,” she told SM, adding that as gold is already mined from rocks it may be possible to adapt these techniques relatively cheaply to extract sewer gold.

She said that as the mining and crushing of rocks are two of the biggest costs associated with gold mining; obtaining the precious metal from incinerated sewage ash could be much cheaper and more environmentally friendly.

“The ash is where it’s concentrated so it makes sense to extract it from there,” she said.

She added that countries such as India and Japan already extracted gold from sewers but that these countries used different methods, as the metal was present in far higher concentrations.

Most of the gold extracted in Japan is believed to be industrial gold, in a largely secret process. She believes that in India it is extracted by panning raw sewage.  

Dr Prichard added that her research also indicated levels of silver and platinum as well as rhodium and palladium that could be economically viable to extract. These last two rare metals are most commonly used in automobile catalytic converters.

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