There's Gold in Them Thar Hills of Solid Waste

A cloud with a silver lining pales next to solid waste laced with gold

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You can't make a silk purse out of a sow's ear. You can't make chicken salad out of chicken—shall we agree we know what word goes at the end of that saying? It's also been thought impossible to, as the Yiddish expression has it, make gold from—sure enough, it's that same word again.

It remains true that you can't gold from feces. But it turns out you can extract enough gold from solid waste to possibly make the effort pay. This excremental explication was performed by one Kathleen Smith, a researcher with the U.S. Geological Survey, at an American Chemical Society meeting held in late March in Denver. The meeting was billed as “Chemistry of Natural Resources,” which includes the stuff produced when nature calls.

Smith has had what appears to be, based on her authorship of nearly 100 scientific publications, a long and distinguished career. She has now discovered that papers with titles such as her “Trace-Metal Sources and Their Release from Mine Wastes: Examples from Humidity Cell Tests of Hard-Rock Mine Waste and from Warrior Basin Coal” garner far less media attention than do press releases headlined “Sewage—Yes, Poop—Could Be a Source of Valuable Metals and Critical Elements.” (Smith's conference presentation was called “Metal Occurrence in and Potential Recovery from Municipal Biosolids,” which we journalist types would probably have ignored, too, to be honest.)

Before we talk about getting the gold out, let's consider how it got in. Most of us are not dining on gold-leaf-covered ice cream, like the kind in the $1,000 sundaes at the New York City restaurant Serendipity 3 (the wealthy customer being the serene dip). Nor are most of us spending more than $400 on a pill filled with shards of gold leaf, the sole purpose of which is to eventually make one's bowel movement, no joke, glitter. A commenter to the online news article discussing this pill helpfully wrote, “You don't need to pay that much. My kid has glittery poos every time he does arts and crafts … just eat regular glitter, it works just fine.”

Geophagy—snacking on small amounts of dirt—is a common practice in some regions. But a 2014 paper in the journal did not find any gold in soil preferred by pregnant women in Tanzania, where eating earth is believed to alleviate morning sickness—even though the study was done in a gold-mining community. (The samples sadly did contain mercury and other toxic metals used in gold mining.) And whereas a dental patient's gold filling may on occasion pop out of a molar and wind up circling the former chewer's drain, that scenario is rarer than hen's teeth.

Seems that the gold winds up in the solid waste well after said waste is originally produced. “There are metals everywhere,” Smith explains in the aforementioned press release, “in your hair care products, detergents, even nanoparticles that are put in socks to prevent bad odors.” When you wash your clothes or yourself, incredibly tiny amounts of these metals, including precious or useful ones such as gold, palladium, vanadium, platinum and silver, get sent to the sewer. And the processing procedures at treatment plants, designed to recover usable water, meld metal with manure—about seven million tons annually.

With that much material, even minimal ingredients can add up to a small fortune. A 2015 study in the journal estimated that a community of a million people could make a pile of sludge every year with an extracted mineral value of $13 million. When Smith and her colleagues examined treated solid waste, they found gold “at the level of a minimal mineral deposit.” Which means that soon it just may be worth trying to separate the wheat from the chaff. Although anything that started as actual wheat will in this analogy become chaff. Eh, it'll all pan out in the end.

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