杏吧原创

(Image: Lubec Memorial Library)

The idea of harvesting precious metals from seawater has attracted swindlers and Nobel chemists alike. Could nanoscience bring the breakthrough?

鈥淚t was a bitter cold night,鈥� Arthur Ryan recalled later. 鈥淕reat cakes of ice were floating about, and we could hear them crunching against the piles.鈥� He and his fellow investor shivered through the night in February 1897 on a rickety jetty near Providence, Rhode聽Island, guarding a hole in the floor of their shack. Hours earlier, Prescott Jernegan聽鈥� Baptist minister, gentleman scientist and inventor聽鈥� had lowered an 鈥渁ccumulator box鈥� through it into the waters of Narragansett Bay below.

The next morning, on prising open the box, the bleary-eyed men had their reward: gold. But all was not quite as it seemed鈥�

ADVENTURERS have long dreamed of treasure from the sea. Usually they have booty from bygone eras in their sights 鈥� 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 鈥淏lack Sam鈥� Bellamy鈥檚 flagship, , and the treasure-hunters had to penetrate several feet of dark and slimy ocean-floor seaweed to reach them: like 鈥渄iving in a vat of black gelatin鈥�, .

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鈥檚 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鈥檚 method successfully extended the principle to seawater.

鈥淭HE OCEAN A GOLD MINE,鈥� 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 鈥淣ew Klondike鈥�. Locals exulted that prospectors would have 鈥渓ittle need of a trip to Alaska in the future鈥�. The first sea gold made its way into the hands of assayers in early 1898.

Lubec boomed, and a huge 鈥淧lant #2鈥� 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 鈥渒ettle-shaped machines, 30 inches across, overflowing with water all the time from the pipes鈥�. They were clammy with slime and mercury 鈥� 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鈥檚 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鈥檚 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. 鈥淎ll of our efforts were for the liberation of the fatherland,鈥� 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. 鈥淚 have given up looking for this dubious needle in a haystack,鈥� Haber finally conceded.

鈥淣obel laureate Fritz Haber posed as crew on a transatlantic liner, while surreptitiously testing the sea for gold鈥�

Attention turned to other elements that seawater holds in abundance (see 鈥�Nuclear submarine鈥�), but the irony of many of these efforts is that they were not necessarily wrong in principle 鈥� just before their time. Contaminated samples and poor measurements led early researchers astray about how much gold is actually in seawater. Haber鈥檚 initial estimates, for instance, were two to three orders of magnitude too large.

鈥淭he concentration of this precious metal in seawater is on the order of parts per trillion鈥� [It鈥檚] very difficult to measure,鈥� 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 Sillanp盲盲 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鈥檚 interest was spurred by the traditional use of gold in Indian medicine 鈥� 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 鈥渟alting鈥� 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鈥檚 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鈥檚 鈥渟ea gold鈥�. The real stuff is still out there, however, just waiting to be recovered.

This article appeared in print under the headline 鈥淕old tidings鈥�