Mercury recycling could save lives | Science| In-depth reporting on science and technology | DW | 16.05.2012
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Science

Mercury recycling could save lives

Mercury is a toxic heavy metal still used in masses of everyday products. Disposing of it, experts say, requires advanced technology - and it could save children's lives in develeoping countries.

Young people in many emerging countries continue to risk their health - and lives - dismantling electrical and electronic devices that contain mercury.

Indiais a prime example, according to Jochen Flasbarth, president of Germany's Federal Environment Agency, who recently travelled to India and observed local methods of recycling electronic components.

"There you see mostly children in homes and apartments dismantling computers and other electronic devices, as well as electrical lamps, by hand - without any knowledge of the health hazards," he said. "It's a shocking sight."

EU mercury export ban

To protect people against such hazards, the EU imposed an export ban on mercury in March 2011. Within the EU, the toxic substance now has to be disposed of in an environmentally-friendly way.

Germany's largest recycling company, DELA in Essen, specializes in separating mercury from products and disposing of it safely.

Revolving cylindrical furnance

A revolving cylindrical furnance processes mercury-contaminated materials

Trucks regularly arrive at the recycler full of used florescent tubes. Fork-lift operators remove pallets full of the tubes and dump them into large hoppers. A powerful ventilation system keeps the air free of poisonous mercury fumes.

The tubes are then shredded and transported to a silo, where two tons of newly shredded glass are added every hour, according to DELA's managing director, Christian Bonmann.

From there, the crushed lamp glass is pushed through pipes to a broken-glass washer.

"We free the shredded lamps of the fluorescent powder by rinsing the pieces with clean water until they are pollution-free," Bonmann said. "The metal and glass are separated up front by a sieve. We then ship the metal and glass back to the manufacturers."

In addition to the glass and metal, a white sludge remains. It is rich in illuminates, which contain precious metals, such as yttrium and europium.

But the sludge also contains mercury.

So, in a next step - to separate the mercury from the illuminates - the sludge is poured into a vacuum dryer, which functions much like a clothes dryer.

Once the sludge is dry, it's put into a vacuum and heated to 370 degrees Celsius to vaporize the mercury. Like a schnapps distillery, the mercury vapour enters a condenser and drips out, producing pure mercury.

Rotary kiln

The process also produces pollution-free illuminates, which light-bulb manufacturers can in turn use.

DELA also operates a revolving cylindrical furnace, which is three meters high and about twice as long. It can process all sorts of mercury-contaminated materials, particularly filters from coal-fired power plants and waster incinerators.

Vacuum dryher

Sludge is poured into a vacuum dryer

Even contaminated soil and rubble can be freed of mercury in the rotary kiln. The waste is heated to between 550 and 850 degrees Celsius. At those temperatures, mercury vaporizes into a flue gas.

The flue gas then passes through several cleaning stages, including a scrubbing that uses water for quick cooling. As a result, the vaporized mercury condenses and the mercury is separated.

As with the lamp recycling, a valuable sludge remains at the end of the process. In addition to mercury, the sludge contains other valuable metals, which are recovered, such as molybdenum from catalysts.

The remaining pure mercury is rendered harmless through another process, according to DELA engineer, Ulrich Augustat.

"With the help of sulphur, we convert mercury to mercury sulphide," Augustat said. "The substance, with its fiery red color, was used in the past by artists to make red paint. The fact that many of these artists lived long lives is proof that it's not too harmful to handle mercury sulphide."

At the very least, mercury sulphide is rendered so chemically stable and poision-free that it can be safely stored, permanently, underground.

Author: Fabian Schmidt / jrb
Editor: Zulfikar Abbany

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