It’s been said that the economy of New Caledonia beats to the rhythm of the world’s appetite for nickel. The metal-rich soils of the South Pacific island chain, which lies about 750 miles east of Australia, contain about 10 percent of the world’s known nickel reserves, according to the United States Geological Survey, and mining for the metal is the archipelago’s largest industry.
But open-pit mining, which has stripped rainforest and topsoil from the land, has had drastic impacts on natural ecosystems. When it rains, nickel, chromium, cobalt, and manganese, turn the soils “red like rust,” said scientist Arnaud Serres, polluting water catchments and flowing down rivers into the ocean.
Once in the sea, not only do the metals and sediment smother a vast, nearby coral reef system, but they could enter the food chain. Although little is known about the health impacts of nickel exposure via water or food, exposure by inhalation has been linked to allergic reactions, lung inflammation, and lung cancer.
“This could be a big public health problem,” said Serres, who is an assistant professor at the University of New Caledonia.
Serres and some of his colleagues wanted to find out if there was a way to help rid the ocean of such toxic material. The researchers set out to test if a technique commonly used to prevent the corrosion of steel could trap metals found in contaminated water.
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Cathodic protection is commonely used to protect pipelines, the hulls of ships, and the inside of water storage tanks and appliances like washing machines. Protection is achieved in two ways. Either through galvanic anodes or by running an electric current over the metal surface.
In seawater, using an electric current on metals induces the precipitation of magnesium and calcium, which forms a calcerous deposit much like the residue that can build up on the inside of tea kettle.
“We thought why couldn’t we trap and form similar material with something else, for example nickel,” Serres said.
The researchers suspected the metals would be sucked up as the calcerous deposit was formed.
They tested their hypothesis in a laboratory setting by dipping cheap and commercially available galvanized steel electrodes into nickel-enriched seawater and allowing a weak electric current to run through it. After seven days up to 24 percent of the nickel in the original solution was trapped in the calcareous deposit, according to a paper published in Environmental Chemistry Letters earlier this year.
Serres said the method has also been used to trap lead and is being tried with other metals.
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Earlier this month, the researchers moved onto the next phase of testing, applying the method outside of the lab.
A larger-scale experiment is underway in Numbo Bay, an industrial zone in the capital Noumea. A small grid of galvanised iron, connected to the electricity network, has been positioned between the low and high-tide line, and will stay there for about two years.
If the experiment is a success, Serres said, the technology could be used to reduce the concentration of metals in water catchments or at the mouths of rivers that flow into the sea.
“We won’t be able to remove all the pollution from the sea, of course,” he said, “But I think maybe we can reduce the affect of high concentration.”
The first results from the field test will be ready in six months, but already the signs are promising.
“After a few days, the calcerous deposit has formed,” Serres said.
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