Could you ever imagine someone throwing away a commodity as valuable as gold? As difficult as it may be to believe, people are literally flushing millions of dollars worth of gold down the drain each year!
It begs a rather strange pair of questions: How much lost gold is really hidden in our sewer systems? and is there a way to extract all of that "dirty gold"?
Gold Down the Drain
Incredibly, $16 million (£13 million) worth of precious metals are unwittingly flushed into the sewage system of the U.K. alone each year.
That's a lot of treasure being lost to routine waste management!
The same is true in Japan: a sewage treatment facility in Tokyo was finding so much gold content in its sludge that it began collecting the valuable dust from its incinerator.
In the case of the Tokyo sewage treatment, the culprit is likely to be a nearby precision equipment manufacturer that uses gold in the process. Meanwhile, the best explanation for the discovery in the U.K. is actually commonplace activities by local residents. If you wash your hands over the sink while wearing a gold wedding ring, small bits of gold make it into the waste water supply. The same happens when people with gold in their teeth brush over the sink.
You may be wondering if it's even worth it economically to extract the gold from this refuse. Researchers were shocked to find that these processes have gradually added a great deal of gold to sewage waste. We're not talking about negligible, microscopic amounts: In both Japan and the U.K., the concentration of gold in the ashes of incinerated waste was comparable to the world's average gold mine!
These piles of sludge have been yielding between 1 and 3 parts gold per million particles—roughly equivalent with the concentration of gold in a profitable orebody. The facility in Japan recently extracted almost 1.9 kilograms of gold per metric tonne of sewage ash! Even the richest ore from major gold mining projects average a few grams of gold per tonne.
Moreover, in terms of cost, it is far cheaper to sift through ash for gold than it is to refine a hard, rocky mineral ore. Scientists are in the process of developing even more efficient ways to do so, as well.
There are other applications for such precious metal recovery from forgotten waste. The gold and silver from used electronics can be recycled; the bits of platinum and palladium that flake off of car exhausts can be recovered by street sweepers.
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