Abstract
AbstractSamples of incinerator ash from sewage operations in the UK have been analysed and all contain concentrations of over 1 ppm gold (Au), ranging up to 7 ppm, showing a remarkable consistency of enrichment for all the 9 incinerators sampled. Samples analysed from 2005 to 2007 and in 2014 all have elevated values showing a consistency of high Au grades over time as well as between incinerators. One dried sewage sample also has elevated Au values averaging 721 ppb. Rounded grains of Au, 2–3 microns in diameter, have been located in the incinerator ash. Our results indicate that this ash produced from incinerated sewage contains Au, with associated platinum‐group elements (PGE) and silver (Ag). This forms a polymetallic resource which may be economic to recover and recycle. Tests to extract these precious metals from the ash are ongoing.
Highlights
It is becoming increasingly clear that the quantities of precious metals building up in urban waste all over the world are sufficient to warrant investigation with a view to recovery and recycling
Our results indicate that this ash produced from incinerated sewage contains Au, with associated platinum-group elements (PGE) and silver (Ag)
Mineralogical studies show that the Pt and Pd are present as multiple nanoparticles attached to catalytic converter fragments (Prichard and Fisher 2012) and Pt and Pd are not located at the bottom of drains (Prichard et al 2009)
Summary
It is becoming increasingly clear that the quantities of precious metals building up in urban waste all over the world are sufficient to warrant investigation with a view to recovery and recycling. More than 50% of all the annual production of platinum (Pt), palladium (Pd) and rhodium (Rh) are used in the manufacture of these catalytic converters (Cowley 2013) and during operation these precious metals are ejected onto roads. They concentrate in road dust at levels that are extremely enriched compared to normal background levels of less than 1 ppb. From roads these precious metals are dispersed into the environment (Rauch et al 2005; Jackson et al 2007; Prichard et al 2009)
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