(Image: Lubec Memorial Library)
The idea of harvesting precious metals from seawater has attracted swindlers and Nobel chemists alike. Could nanoscience bring the breakthrough?
“It was a bitter cold night,” Arthur Ryan recalled later. “Great cakes of ice were floating about, and we could hear them crunching against the piles.” He and his fellow investor shivered through the night in February 1897 on a rickety jetty near Providence, Rhode Island, guarding a hole in the floor of their shack. Hours earlier, Prescott Jernegan – Baptist minister, gentleman scientist and inventor – had lowered an “accumulator box” through it into the waters of Narragansett Bay below.
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The next morning, on prising open the box, the bleary-eyed men had their reward: gold. But all was not quite as it seemed…
ADVENTURERS have long dreamed of treasure from the sea. Usually they have booty from bygone eras in their sights – as happened this September, for example, when divers discovered a hoard of gold coins off Cape Cod, Massachusetts. The coins most probably came from the 1717 wreck of pirate “Black Sam” Bellamy’s flagship, , and the treasure-hunters had to penetrate several feet of dark and slimy ocean-floor seaweed to reach them: like “diving in a vat of black gelatin”, .
It was Italian chemist Faustino Malaguti who first raised the promise of marine bounty a little closer to the surface. In 1850, he discovered that seawater itself contains silver chloride, raising the question of how the silver might be extracted. In an address to the British Association in Birmingham in 1865, the former governor of Hong Kong, John Bowring, , so that they might electroplate themselves in riches.
The discovery of gold in seawater in 1872 only increased the allure. Even with the gold content then estimated at less than 1 grain per tonne of water, that meant a lot of precious metal sloshing about the globe. By the 1890s, new techniques for leaching gold out of solution using cyanide seemed to provide a way to recover it. Interest was particularly keen in Australia, with its thriving mining industry and extensive coastline. In 1896, the eminent chemist Archibald Liversidge of the University of Sydney experimented with collecting mineral accretions from brass plates suspended under wharves.
Prescott Jernegan’s process, announced just a year later, was an apparent breakthrough. The reverend kept the details of what went on within his accumulator boxes secret from his eager investors by refusing to patent it, but it involved electricity, thin platinum wire and mercury. Mercury, at least, was a familiar part of extraction processes already used in California and the Klondike: when gold-containing ore was washed over mercury, the elements precipitated out as an amalgam, allowing the gold to be recovered. The golden flecks found on the mercury when Ryan and his associate opened their accumulator box were the proof that Jernegan’s method successfully extended the principle to seawater.
“THE OCEAN A GOLD MINE,” crowed newspapers. launched in 1897 with nearly $1 million in stock and 293 accumulators kept in a well-guarded old grist mill in Lubec, Maine, a coastal town soon dubbed the “New Klondike”. Locals exulted that prospectors would have “little need of a trip to Alaska in the future”. The first sea gold made its way into the hands of assayers in early 1898.
Lubec boomed, and a huge “Plant #2” was planned to place thousands of accumulators in tidal waters, with 700 labourers hired to build it. Lubec got its first phone line, a new bridge, and a company boat dubbed The Gold Bug.
Nanoparticles not nuggets
The end came with shocking speed. Workers arriving at Plant #2 on 28 July 1898 discovered that Jernegan and his confederate Charles Fisher had skipped town with about $300,000 in company funds. Reporters looking in the accumulator rooms found “kettle-shaped machines, 30 inches across, overflowing with water all the time from the pipes”. They were clammy with slime and mercury – but no gold.
It was not the end of dreams of riches from the sea, however. In Australia and England, two separate ventures launched in 1904. The Australian attempt was reassuringly backed by mining engineer Albert Argle’s own money, and his pilot plant at Broken Head, New South Wales, used a proven technology, the MacArthur-Forrest cyanide leaching process. A similar plant at Hayling Island on the south coast of England boasted the endorsement of Nobel laureate .
Both schemes failed, but marine gold remained a challenge worthy of a Nobel chemist. Amid Germany’s hyper-inflation of 1923, laureate was put on a secret mission to discover , and so help his country pay off its crushing first world war reparation payments. “All of our efforts were for the liberation of the fatherland,” he recalled. Haber and his staff posed as crew on the passenger liner Hansa, while surreptitiously testing the waters of the Atlantic. Alas, there was better money in swabbing the decks than in seawater. “I have given up looking for this dubious needle in a haystack,” Haber finally conceded.
“Nobel laureate Fritz Haber posed as crew on a transatlantic liner, while surreptitiously testing the sea for gold”
Attention turned to other elements that seawater holds in abundance (see “Nuclear submarine“), but the irony of many of these efforts is that they were not necessarily wrong in principle – just before their time. Contaminated samples and poor measurements led early researchers astray about how much gold is actually in seawater. Haber’s initial estimates, for instance, were two to three orders of magnitude too large.
“The concentration of this precious metal in seawater is on the order of parts per trillion… [It’s] very difficult to measure,” says , a chemist at the University of Southampton in the UK. But with modern techniques, and for those that seek nanoparticles rather than nuggets, the sea could still hold rich promise.
Earlier this year, Lodeiro and his colleague Mika Sillanpää from the Lappeenranta University of Technology in Finland showed how nanoscale particles of gold could be recovered from artificial seawater enriched with the precious element in parts-per-million concentration. Their experiments used two commercially available agents for removing metallic ions from solution, and also a coarse powder of brown seaweed, Sargassum muticum, which is known to have a high affinity for heavy metals (). Lodeiro is now looking to move the testing from the lab to less-concentrated gold in real marine conditions.
Meanwhile, of the Institute of Microbial Technology in Chandigarh, India, and his colleagues have been exploring the use of bacteria in metal-rich water that excrete gold nanoparticles (). Choudhury’s interest was spurred by the traditional use of gold in Indian medicine – for instance, the gold-containing powder, , which is used to treat a variety of conditions such as asthma and arthritis in traditional ayurvedic medicine.
This history is now finding new life, as the tendency of gold nanoparticles to accumulate in cancer cells leads to their adoption as components of cell imaging and targeted drug-delivery systems. The active chemistry and tunable optical and electronic properties of gold nanoparticles are also making them increasingly in demand for catalysis and use in microchips and photovoltaic cells. Processes for making gold nanoparticles in the lab are fiddly and often involve the use of environmentally suspect caustic chemicals, so it is no surprise that freely available seawater is seen as a tempting alternative source. Dreams of riches from the sea have come a long way since the simple money lust of Prescott Jernegan.
The secret of his method turned out to be his accomplice, Fisher, who was “salting” the accumulators with gold all along. Fisher even allegedly donned a diving suit to add in gold as investors waited on the wharf above, a claim Jernegan later stoutly denied. Years later, residents in Fisher’s former house discovered a hidden panel, behind which was a stash of old jewellery ready for melting. That was the true source of the reverend’s “sea gold”. The real stuff is still out there, however, just waiting to be recovered.
Nuclear submarine
The sheer quantity of seawater out there means that even when elements exist only in trace quantities, they add up to a vast potential resource. Bromine, magnesium and iodine are already profitably extracted from the sea. Of heavier elements, besides gold (see main story) uranium has long aroused interest. The few parts per billion found in seawater, mostly as the ion uranyl, is enough fuel to power the planet’s nuclear power plants for thousands of years.
Attempts to extract this uranium have a long history. In 1964, the UK’s Atomic Energy Research Establishment tried harvesting it from the waters off Portland Bill on the south coast of England using titanium hydroxide, which bonds with uranyl (). In the 1970s, German researchers to absorb high concentrations of heavy metals like uranium. Neither technique is yet competitive with conventional mining, but they have been of ongoing interest above all to the mineral-poor and nuclear-dependent island of Japan.
More recent approaches include sinking plastic matting soaked with the uranium-absorbent amidoxime into the sea, and the use of compounds known as metal-organic frameworks that have a particular affinity for uranium (). The hope is that even if such extraction techniques fail to make the grade for commercial mining, they may prove valuable for treating radioactive wastewater.
This article appeared in print under the headline “Gold tidings”
