Claims that rare earth metals, even gold, might be profitably recycled from poop have been circulating around the interwebs(Opens in a new window). Does this make any sense, or is it just an example of recyclemania running wild? The idea was brought to the fore following a recent meeting of the American Chemical Society in Denver. There Kathleen Smith from the US Geological Survey (USGS) reported that the body offloads this swag at concentrations on par with the level of a minimal mineral deposit.
Their biosolids data indicates that in each kilogram of human waste, there is an average of around 30mg of silver, 40 mg of vanadium, and 640mg of copper, in addition to significant amounts of gold and palladium. All told they say, we might be talking up to $13 million annually in the waste of 1 million U.S. citizens. Approached another way, the average 70kg body would contain less than a milligram of gold, an amount equal to about $0.009. Unless you subsidize by regularly indulging in gold-flecked ice cream at Dubai's Scoopi cafe(Opens in a new window), or artificially enhance your flesh tones with silver as the late 'blue man' did to treat a skin condition (pictured right), you aren't going to get much.
In the past, sober minds have asked if it would be worth their while to extract metals from sea water. Eight million tons of gold, or about 1 mg per kg can be found there. Unfortunately, without a way to specifically pre-concentrate on truly massive scales, as seaweed does to provide us with iodine, even sea water is a non-starter. One the other hand, if what you seek is many times more valuable than any metal, the economics might makes more sense.
For example, when penicillin was first used, it was found that almost all of it showed up in the urine completely unmetabolized within just a few hours. It could then be extracted after the urine was crystallized and used to treat bacterial infections in the next patient. For some of today's rarefied cancer medicines costing upwards of $1,000 per dose, this is certainly something to consider. Another fine example of when it actually pays to reclaim stuff on a per-molecule basis is in extracting rhenium from used turbine blades. Here, niche recycling outfits can turn a slight profit by electrolytically accumulating the metal, albeit with considerable assist from the power grid.
The main problem in envisioning waste as a source for rare earths is that rare earths aren't really rare. In the countries that produce them, a rare earth harvest is better thought of as a side effect of a healthy steel harvest. The reason companies here can't dig up the monazite deposits abundant in rare earths is that they are "contaminated" with thorium. Thorium! Any self-regulated civilization that is looking at thorium today, a very mild low-alpha emitter, and seeing bad, can't possibly be seeing straight.
While the conclusion here is that human waste won't ever become a prized source of exotic metals, we would offer that the real value in human waste is the information it contains. Toilets that recycle water may not ever become a favored source of tap water -- but those that produce local data, which can then be compared with more centrally pooled data, may eventually be ubiquitous. Not everyone will want or need this information, but as a diagnostic service, it may become one we would be unwise not to avail ourselves of.
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