Science - USA (2020-08-21)

P

ractical and glamorous, aluminum

is prized for making products from

kitchen foil and beverage cans

to Tesla Roadsters and aircraft.

But the silvery metal—abundant,

cheap, lightweight, and corrosion

resistant—has a dark side: red

mud. This brownish red slurry, a

caustic mishmash of metal- and

silicon-rich oxides, often with a dash of ra-

dioactive and rare earth elements, is what’s

left after aluminum is extracted from ore.

And it is piling up. Globally, some 3 billion

tons of red mud are now stored in massive

waste ponds or dried mounds, making it

one of the most abundant industrial wastes

on the planet. Aluminum plants generate

an additional 150 million tons each year.

Red mud has become trouble looking for

a place to happen. In 2010, an earthen dam

at one waste pond in Hungary gave way, un-

leashing a 2-meter-high wall of red mud that

buried the town of Ajka, killing 10 people and

giving 150 severe chemical burns. (For more

on the dangers posed by waste dams, see p.

907.) Even when red mud remains contained,

its extreme alkalinity can leach out, poison

groundwater, and contaminate nearby rivers

and ecosystems. Such liabilities, as well as

growing regulatory pressure on industry to

develop sustainable practices, have catalyzed

global efforts to find ways to recycle and re-

use red mud. Some researchers are develop-

ing ways to extract the valuable rare earth

metals, whereas others turn the mud into ce-

ment or bricks.

“There is hope here,” says Yiannis

Pontikes, a mechanical engineer at the

Catholic University of Leuven. But eco-

nomic and marketing hurdles remain, and

“the clock is ticking” as regulators consider

new controls, says Efthymios Balomenos, a

metallurgical engineer at the National Tech-

nical University of Athens. “At some point

we will not be able to produce waste. So,

there is an urgent need to make changes.”

ALUMINUM IS ONE of the most commonly

recycled materials, with 75% of all alumi-

num ever produced still in use. But there

is an ever-burgeoning demand. Aluminum

sciencemag.org SCIENCE

Researchers are working to find new

uses for red mud, the caustic byproduct

of aluminum production

By Robert F. Service

RED ALERT

PHOTO: BELA SZANDELSZKY/AP PHOTO

910 21 AUGUST 2020 • VOL 369 ISSUE 6506

Published by AAAS