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Rio's lithium 'eureka' moment

RIO Tinto believes it could become the US’s largest producer of battery grade lithium without needing to mine anything.

The company revealed it was working on a breakthrough process that could generate battery grade lithium carbonate from waste rock at its Boron mine in California.

The discovery came after the team was looking for gold and other minerals in the waste rock and found that parts of the piles had higher grade lithium than some US development projects.

"Our team had a eureka moment when they did some testing to look for valuable minerals beyond boron in our waste rock and found high grades of lithium," Rio Energy & Minerals chief Bold Baatar said.

"If the trials continue to prove successful, this has the potential to become America's largest domestic producer of battery grade lithium - all without the need for further mining."

There is 90 years' worth of waste rock at Boron.

An initial small-scale trial has shown the lithium can be recovered via roasting and leaching.

Baatar said the project had sustainability benefits.

"The material being used has already been mined, so this will be a low energy option for the production of lithium," he said.

"It's a great example of the innovative thinking we are encouraging, to look at extracting additional value from our tailings, look outside our traditional commodities and not be afraid to try new approaches."

The challenge for the Boron team now is to optimise the process with an aim to achieve commercial lithium production.

A pilot plant is being assembled that will have the capacity to produce 10 tonnes per year of lithium carbonate equivalent, and is being fed by a rotary kiln.

The tests will run for several months, but Rio expects its investment to reach US$10 million in the current phase.

If successful, a $50 million industrial-scale plant to produce 5000tpa of LCE would be built.

Rio has been interested in lithium for some time, and is working towards a development decision for its Jadar project in Serbia.

The production of jadarite, or lithium sodium borosilicate, would be a world-first.

MNN also understands Rio was in the Kidman Resources data room prior to its A$776 million takeover by Wesfarmers.

The company is also looking to produce monazite from waste in Madagascar, and optimise production of rhenium from the Kennecott copper mine in Arizona.

Monazite contains 50% rare earths, which, along with rhenium, is on the US's critical minerals list.