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Science & Technology

June 8, 2009
Volume 87, Number 23
pp. 53-57

Future Of Metals

Developing sustainable supplies of metals will rely on smart product design and more efficient recycling

Stephen K. Ritter

LITHIUM POND Lithium-laden brine evaporates at Chemetall’s Salar de Atacama site in Chile, one of the world’s largest lithium mines. Chemetall
LITHIUM POND Lithium-laden brine evaporates at Chemetall’s Salar de Atacama site in Chile, one of the world’s largest lithium mines.
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BARRELS OF CATALYSTS: At Umicore's facility in Hoboken, Belgium, the guts of car catalytic converters await recycling to recover the valuable metals coated on the cordierite mineral substrate. Umicore
BARRELS OF CATALYSTS At Umicore's facility in Hoboken, Belgium, the guts of car catalytic converters await recycling to recover the valuable metals coated on the cordierite mineral substrate.
BLACK SMOKER CHIMNEY A midocean hydrothermal vent, as seen through the viewport of WHOI's submersible <em>Alvin,</em> spews out metal sulfides and other chemicals that precipitate to form potentially minable deposits. Pat Hickey/WHOI
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BLACK SMOKER CHIMNEY A midocean hydrothermal vent, as seen through the viewport of WHOI's submersible Alvin, spews out metal sulfides and other chemicals that precipitate to form potentially minable deposits.
Ocean Harvest: A recovered piece of a hydrothermal vent chimney is rich in iron, copper, zinc, and lead. Tom Kleindinst/WHOI
Ocean Harvest A recovered piece of a hydrothermal vent chimney is rich in iron, copper, zinc, and lead.
Metal Evolution: Yale's Graedel, hoiding a computer circuit board and a lump of copper ore, has extensively studied the supply and demand of metals, concluding that sustainable cycling of metals will become necessary. Harol Shaprio/Yale
Metal Evolution Yale's Graedel, hoiding a computer circuit board and a lump of copper ore, has extensively studied the supply and demand of metals, concluding that sustainable cycling of metals will become necessary.

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Could metals become extinct? That question has popped up in magazine articles and in the blogosphere in response to predictions by several scientists—taken out of context—that some metals running up against high demand and low supply could go the way of the dinosaurs.

Metals can’t really become extinct because their atoms are immutable, at least under most conditions. But it’s not such a farfetched idea that as world population and the average standard of living increase, some metals could become unavailable for new uses.

That realization is inspiring some scientists and economists to develop forward-thinking approaches to achieving sustainable cycles of metal use—that is, a continuous supply loop of a metal that runs from starting material to product to end-of-life recycling and back to starting material, with minor additions of virgin metal as needed to balance any inevitable processing losses.

“Metals have limits in the same way that crude oil and clean water do,” observes Yale University’s Thomas E. Graedel, an industrial ecologist who has been exploring natural resource limits for many years. Graedel and his colleagues’ analyses of the supply and demand of metals has led them to an understanding that if current consumer trends continue, the supply of some metals will soon become strongly limited unless action is taken.

“It means we need to develop sustainable in-use stocks of metals,” Graedel says. Maintaining these perpetual metal supplies will require smarter product design that “allows us to continue to achieve the high performance of materials that we desire but ensures efficient metal recycling,” he adds.

The chemistry enterprise actually doesn’t use much metal day-to-day, Graedel notes. Metals primarily are consumed by manufacturing industries. But chemists and chemical engineers still have a leading role to play in the future of metals by designing products and developing processes that are ultimately responsible for how global metal resources are extracted, processed, and used.

Graedel and his colleagues have been assessing the amount of unmined metals, metals in current use, and metals disposed of as waste. Of the elements they have examined, they have singled out copper, zinc, and platinum as endangered species whose supplies could be in trouble before the end of the century. Other scientists have pinpointed gallium, indium, and hafnium as potentially running short, possibly within the next decade.

These metals are being extracted from Earth and put into service at rates faster than they are being recycled, Graedel says. In some cases there is more of the metal already in use above the ground than there is left in the ground.

That’s not necessarily bad news, Graedel says. For some metals it could mean eventually running out of sources to mine and moving toward full dependence on recycled metals. On the basis of his group’s calculations, Graedel concludes that the in-use stocks of the most commonly used metals—aluminum, copper, iron, lead, and zinc—would have to increase three to nine times their current amounts to satisfy the wants and needs of the global population and reach the critical mass that could support the sustainable cycling that he is advocating.

Preparing for potential limits on metal availability will require a new level of up-front decision-making, Graedel adds. For example, engineers may not want to design an electronic device that will keep a particular metal tied up in a single application for a long time if we know that metal could end up in short supply, he says.

As for recycling, Graedel suggests that cities will become “anthropogenic mines” for metals that are no longer in service. “Our problem is that we aren’t very good at extracting the metals from these urban mines because they come disguised as computers, automobiles, and buildings,” Graedel says. “We need to do a better job of grabbing those metals for recycling, which means we need to be doing a better job of product design to allow for this recovery. Metal shortages are going to push us to become more innovative designers and more efficient recyclers.”

The chemical, petroleum, and pharmaceutical industries already have set the standard for recycling metals when it comes to platinum group metal (PGM) catalysts. PGM catalysts, which include platinum, palladium, rhodium, ruthenium, and iridium, are high-value commodities with relatively long life cycles, notes Christian Hagelüken, business development and marketing manager of Umicore Precious Metals Refining, in Hoboken, Belgium, the world’s leading PGM recycler.

When an industrial catalyst needs to be replaced, the catalyst owner ships the material to Umicore or another recycler to be refined, Hagelüken explains. The recovered PGMs are used to produce new catalyst, which is returned to the customer. This type of business-to-business closed-loop recycling guarantees very little metal drops out of service—only a residual amount is lost in the catalytic process or in the reprocessing, Hagelüken says.

This closed system works well for a captive application like high-value industrial catalysts, but most other materials recycled for their metals are consumer products characterized by an open-loop recycling structure, Hagelüken says. In the latter case the product, such as a computer or a car and its catalytic converter, often has multiple handlers or owners during its life cycle with no clear responsibility or incentive for anyone to recycle the metal.

Although effective recycling technologies exist to handle these materials, most of them still don’t make it into the recycling stream and break the loop. For example, only about 50% of PGMs from automobile catalysts are recovered, primarily because of a lack of appropriate end-of-life management, Hagelüken notes. The remaining 50% represents an important source of metal supply, if it can be captured, he says. In a more compelling example, the Environmental Protection Agency estimates that in the U.S. only 18% of electronics such as TVs and computers and only 10% of cell phones are currently recycled to recover PGMs, gold, silver, and other metals.

For its part, Umicore has developed a state-of-the-art integrated smelter-refinery to process PGMs and other metals. The facility processes about 1,000 metric tons per day of a mix of industrial PGMs and other catalysts, catalytic converters, computer circuit boards, cell phones, precious-metal-containing smelter by-products, and more.

These materials, which come in from chemical and car companies, metallurgical plants, and commercial recyclers, are first individually milled and assayed to determine the exact metal content. The material is then mixed with other recyclables in a giant smelter, which is fired up to 1,200 °C to create a molten mix of metals. A subsequent series of chemical and physical steps separates and purifies the metals.

Major products like copper, lead, and nickel are separated early in the process and can be sold on the open metals market. The process stream continues through additional metallurgical machinations to refine 14 other metals including the PGMs, gold, silver, selenium, tellurium, and indium. Metals such as PGMs from industrial catalysts that are in a closed-loop process are returned to the owner. Umicore, which is a leading manufacturer of PGM catalysts and other metal products, uses other recovered metals as raw material or sells them.

The volume of PGMs currently in use remains small, Hagelüken says, adding up to a total of about 2,700 metric tons in cars and 1,000 metric tons in catalysts and other applications. Some 500 metric tons of new PGMs are produced each year from mines located primarily in Russia and South Africa. That volume makes it easier to operate in a closed-loop format, he notes.

Hagelüken would like to see the closed-loop model extended to include a host of other materials, including car catalytic converters, consumer electronics, and emerging areas such as photovoltaic solar cells, fuel cells, and electric car batteries. Improving closed-loop recycling will also head off inefficient and hazardous roadside or backyard recycling taking place in developing countries in Africa and Asia, he adds.

“Building up a more sustainable society with the help of technology depends to a large extent on sufficient access to technology metals,” Hagelüken says. “Because of the low relative abundance of these metals and their high cost, it’s necessary to establish effective recycling systems to preserve our limited metal resources.”

Some ideas Hagelüken has put forth to possibly accelerate adoption of closed-loop recycling include financial incentives such as leasing or placing deposits on the products or on the metals in catalytic converters, cell phones, computers, and televisions. Such steps, he says, could ensure the metals will enter end-of-life processing and emerge for another go-around.

While PGMs offer a proven example of managing metals on a small scale, lithium could be the model for successfully managing a metal on a large scale. Although lithium has many uses—in ceramics and glass, lubricating greases, organolithium reagents for pharmaceuticals and polymer production, and small rechargeable batteries—the application on most people’s minds these days is the next-generation replacement of nickel metal hydride battery packs in hybrid-electric cars.

The sudden production of lithium batteries for millions of cars—which require about 10 lb of lithium per battery pack—could dishevel the lithium supply chain. But in an effort to head off potential problems, lithium mining companies, battery producers, and automakers have been working together to thoroughly analyze lithium availability and future recyclability before adopting new lithium-ion chemistries, notes Brian W. Jaskula, a U.S. Geological Survey (USGS) scientist who tracks lithium, gallium, and beryllium supply and demand. At the latest meeting among these lithium stakeholders in Santiago, Chile, in January, there was consensus that there will be enough lithium to meet demand for car batteries with plenty of room to spare, Jaskula says.

Globally, some 17.7 million metric tons of minable lithium reserves are known, according to the latest USGS figures, with about 9.4 million metric tons of that amount economically accessible with current technology. The current global leaders of lithium reserves include Chile with 7.5 million metric tons, Bolivia with 5.4 million metric tons, Argentina with 2.2 million metric tons, and China with 1.1 million metric tons.

Today’s global lithium production for all uses, approximately 27,000 metric tons per year according to USGS numbers, barely registers as a blip against the total, Jaskula says. Even if demand doubles several times in the coming decades, there will be enough lithium available, possibly without tapping any new mining sites and even without recycling, which is currently more expensive than obtaining new stocks of the metal, he points out.

Most lithium is obtained from underground brine pools in remote desert regions, Jaskula explains. For example, in Chile lithium brines reside just under the surface of the Salar de Atacama, a vast salt flat in the northern part of the country.

Water from the slopes of the Andes Mountains percolates under the surface of the salar, dissolving lithium, potassium, and other salts. To produce lithium, the brine, containing about 2,200 ppm of lithium, is pumped into aboveground ponds where the water evaporates in the desert sun and extraneous minerals precipitate out, Jaskula says. The resulting concentrated lithium slush is then trucked to a processing plant where the lithium is converted to Li2CO3 for making battery electrode materials or to LiOH and LiCl for other applications.

Like with other natural resources, making the connection between known resources and the actual amount of that material that can economically be extracted and utilized is difficult, and misinformation can be rampant, Jaskula says. For example, global energy economists just last year were hailing Bolivia as the “Saudi Arabia of lithium,” because the country’s Salar de Uyuni, just across the border from Chile, was thought to possess 50% of global lithium reserves. However, those numbers were recently revised, Jaskula notes, reanointing Chile as the world leader.

So far, because of a lack of infrastructure, none of Bolivia’s lithium is even being produced commercially, he says. It will take years before Bolivia will be able to produce lithium, Jaskula says, and by then Bolivia could “end up missing the lithium express.”

Lithium’s current overabundance is rare in the world of metals. Should some metals from traditional mining sources become scarce, there is a fail safe option in the form of the vast untapped resource of metals available in the oceans.

“The Earth is a metal-rich rock,” says geologist Maurice A. Tivey of Woods Hole Oceanographic Institution (WHOI). “I can’t see the human race running out of metals when it will be possible to mine in new places or recycle or simply reduce consumption,” he says. “We probably won’t be able to live on the planet due to global warming or other environmental problems before we run into a metal supply problem.”

Tivey, who studies the deep-sea environment, is part of a community of scientists, mining company representatives, and government officials who met at WHOI in April to keep an eye on the prospects of mining metal sulfide deposits that have formed at deep-sea hydrothermal vents in the oceans. Water seeps into the seafloor through cracks along the mid-ocean ridges and becomes heated at these volcanically active boundaries of Earth’s tectonic plates, Tivey explains. The resulting hydrothermal fluid, as acidic as stomach acid and up to 400 °C, gushes out of the vent openings like a geyser, carrying with it dissolved minerals. As the fluid cools near the surface and is ejected into the ocean, metal sulfides precipitate out and form chimneys and mounds that contain iron, copper, zinc, and lead, with trace amounts of gold, silver, and a dozen other metals.

“We have found some 300 hydrothermal vent systems—dead or alive—on the seafloor,” Tivey says. Of these, only about 100 host metal sulfide deposits, he says. The largest deposit is in the Red Sea, with an estimated 90 million metric tons of ore, which is comparable to an average-sized ore deposit on land.

What makes the seafloor attractive for mining is the “open access” of the deposits, Tivey notes. They are right on the seafloor, compared with digging through kilometers of rock on land, he says. Technology developed by oil firms for deep-water drilling and remotely operated vehicles developed for scientific exploration of the deep ocean are making mining in these deep-sea settings feasible. But he and his colleagues want the mining industry to proceed cautiously to preserve the exotic life around the hydrothermal vents, which includes giant clams, superlong tubeworms, and eyeless shrimp.

Besides metal sulfide deposits, another intriguing deep-sea metal resource is manganese nodules. These golf-ball- to tennis-ball-size lumps lie in the sediment scattered over vast swaths of the central Pacific Ocean and in smaller areas of the Atlantic and Indian Oceans. The nodules form over millions of years by slow precipitation of metals from the water above and the water-logged sediment below.

Manganese is the principal metal in the nodules, making up about 18% of the average nodule, followed by iron at about 12% and by small amounts of nickel, copper, cobalt, zinc, and a handful of other elements. Even so, the amount of manganese, nickel, and cobalt in the nodules is estimated to exceed the total amount of known metal deposits on dry land. The problem with nodules, which could be picked up from the seafloor like snatching up marbles, is that they are three miles or more under water.

Although metal sulfides and manganese nodules might not be economical for recovering metals right now, nor may it ever be environmentally wise, the consolation prize is in knowing that there are metals out there if humanity fails in its attempts to develop sustainable flows of metals and aboveground metal “extinction” ever truly becomes a reality.

Going Green

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2011 American Chemical Society
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