SALAR CENTENARIO, Argentina, July 10 (Reuters) - In a

dusty plain in northern Argentina's mountains, black tubes

stretching two stories high fill a massive tank with salty brine

sucked from deep below ground.

The brine contains lithium, a silvery white metal essential

for making electric vehicle batteries and in high demand as the

world shifts to green energy. French miner Eramet is

attempting to use an innovative technique, known as direct

lithium extraction, or DLE, in a race for cleaner, faster and

cheaper ways to produce the metal with less water.

Unlike traditional methods, there are no pools of brine

spanning the size of football fields where lithium is left

behind after the liquid evaporates in the sun.

DLE, which extracts the metal much more quickly, could be

critical to global production given 70% of the world's lithium

is found in brine, rather than rock or clay.

Eramet is being closely watched by competitors from the U.S.

to Chile that are also working to commercialize DLE. It aims to

pump out its first ton of lithium carbonate in November and

scale up to 24,000 metric tons a year by mid-2025.

The $870 million project in the northern province of Salta

puts Argentina, the world's No. 4 lithium producer, in the

spotlight ahead of projects due online in the country in the

coming months from mining giant Rio Tinto, South Korea's Posco

and Chinese miners Zijin and Ganfeng.

Argentina's new production should about double its

capacity, narrowing the gap with Chile, Latin America's top

producer. Some analysts say it could overtake Chile around the

end of the decade even if hurdles remain.

The exact timing for the ramp-up of Eramet's Centenario

plant, co-owned with Chinese nickel and steel giant Tsingshan,

remains uncertain.

"It's a complex plant," CEO Christel Bories said in an

interview. "The challenge is always, will we be able to reach

the nominal capacity, and when?"

For over a decade, Eramet, which produces manganese, nickel

and mineral sands elsewhere, tried different technologies before

opting to develop a process largely in-house.

The need to tailor the extraction method to a specific brine

deposit, each with its own concentration of lithium and other

metals, is part of DLE's complexity.

It will take time to see if Eramet's strategy pans out, said

Joe Lowry, an industry consultant. "The proof will be sustained

consistent production of battery quality product, and it is too

early to say this will happen with any degree of certainty."

FASTER LITHIUM

The first batch of brine will not be ready for the direct

extraction phase until August, engineers told Reuters last week,

as dozens of workers in red thermal jackets inspected the plant.

Wild vicuna, similar to llamas, darted around the site at an

altitude of 4,000 meters (13,100 ft) five hours' drive from the

nearest city.

Eramet's DLE depends on a tailor-made material that soaks up

lithium from brine like a sponge and sits inside a row of blue

tanks, each big enough to fit an SUV. Impurities like sodium

chloride, or table salt, can then be largely washed away.

The material, called a sorbent, works at room temperature,

unlike some forms of DLE that can require heating, and yields

90% lithium, compared to 40% or 50% in evaporation ponds. The

technique allows Eramet to produce a ton of lithium carbonate in

one week, versus a year with traditional methods.

Eramet plans to ultimately pump brine in a continuous cycle

from 20 nearby wells that stretch 400 meters (1,312 ft) deep.

Before that can happen, it must finish the critical

commissioning phase.

Pipeline valves need to open properly. Computers must sync

with several thousand sensors. An evaporating chamber shaped

like a spaceship has to avoid temperature swings.

"You go step by step, making sure you can get to the next

phase," said engineer Soledad Gamarra. "There's the option to

take pauses, but we really don't want that to happen."

Eramet's process aims to recycle 60% of the water,

eventually moving up to 80%, reflecting the industry's goal to

offset controversy around the large volumes of water required by

many types of DLE, especially in arid areas. International

Battery Metals ( IBATF ), which is close to launching DLE near Salt Lake

City in the U.S. state of Utah, aims to recycle more than 98% of

its water.

Some environmentalists say Eramet's project is the latest

threat to previously untouched salt flats.

"They are a perfect system of equilibrium, of life," said

Mara Puntano, an activist in Salta who represents indigenous

communities.

Eramet will seek certification under the rigorous standards

of the Initiative for Responsible Mining Assurance, and aims to

cut water use and chemicals at a planned second plant, estimated

to cost $800 million.

"Phase two, technology wise, will be a big step of

progress," Tsingshan's South America head, John Li, said in an

interview.

Tsingshan and Eramet will scout for buyers in China and

elsewhere in Asia, they said. Despite a lithium supply glut that

has depressed prices and forced some mining companies to pull

back, Bories said Eramet had a healthy margin, with current

prices more than double its cash costs per ton.