How Lithium Americas will mine and process lithium at Thacker Pass

Lithium is the lightest metal on earth and a crucial material for car and device batteries because of its high energy density.

Lithium Americas is building an open pit mine and a processing facility at Thacker Pass in Northern Nevada to tap what is estimated to be the largest known lithium deposit in the world.

Here is the company's process.

Where does the lithium come from?

The Thacker Pass site is within the McDermitt Caldera, which was formed more than 16 million years ago after a super volcano erupted and formed a basin. A lake formed in that depression and deposited different sediments and minerals.

The world's lithium supply is normally contained in hard rock or dissolved in brine deposits, which are pools of salty groundwater. The clay lithium deposits at Thacker Pass are unusual. The metal was originally contained in glass and ash from volcanic eruptions, eventually leaching into the clay in the caldera.

More than 90 percent of the sedimentary lithium exploration and development projects in the world are located in the U.S., and 75 percent are found in the state of Nevada, said Ryan Long, a managing director at Mining and Metals Research Corp. in the U.K.

How does clay mining differ from the process for other lithium resources?

Hard rock is the most mechanically difficult to mine. Companies crush the rock and use different separation processes to remove the lithium from the ore. Removing impurities is harder than working with lithium mined from brine and clay, but hard rock generally provides the highest-grade lithium. Many hard rock projects only mine their product and sell the ore to companies in China for processing, reducing costs.

Clay is easier to mine because it is close to the surface and soft. Clay refining is also typically cheaper than hard rock processing. The process still requires multiple steps because the clay has to be liquified and the lithium isolated. Lithium contained in clay is generally higher grade than that contained in brine but lower grade than what comes from hard rock. Lithium Americas is both mining and refining its ore on site.

Brine generally contains the largest lithium deposits in terms of scale but the lowest-grade of the three mining options. Brine mining is relatively straightforward — though water intensive — because the lithium is already contained in a liquid. Brine is surfaced and evaporated repeatedly until the lithium has reached peak purity. It is then processed.

Thacker Pass is "an unconventional sedimentary clay deposit; the digging is more or less like an excavation," said David Deckelbaum, a managing director at TD Cowen. "In theory, the purification process is superior to that of hard rock and more analogous to the purification process that you see with brine, because you have the ability to remove more impurities during that separation process."

How will Lithium Americas process its lithium from clay?

Lithium Americas' mining contractor, Sawtooth Mining, a subsidiary of North American Coal, will scoop up the ore that contains lithium from a pit dug to an average depth of 300 feet. The area will be dug up in blocks, and the companies plan to refill the previously mined area and move onto the next. The companies will feed the ore and water to scrubbers that separate sand and gravel from the clay particles containing lithium.

Lithium Americas will then thicken the clay and mix that with a sulfuric acid solution, which creates a metal sulfate brine. The company plans to produce its own sulfuric acid on site, and heat from that process is slated to generate electricity for the processing plant. Other energy will be sourced from hydropower in the Pacific Northwest.

The sulfuric acid will separate the lithium from the clay slurry, and the company will weed out the sand and gravel to save for the backfilling process. The remaining clay will be neutralized and stored in a tailings facility. What's left behind is a solution containing lithium.

The company will remove as much water as possible, crystalize the magnesium sulfate and remove it from the lithium concentrate.

The company said it will reuse this removed water an average of seven times.

It will mix the lithium concentrate with soda ash and centrifuge that mixture. The resulting lithium crystals separated through that process will be further refined, dried, milled, filtered and packaged as battery-grade lithium carbonate.

Despite the complexity of this process, Lithium Americas is essentially combining existing chemical processes.

"They are utilizing more or less off-the-shelf technology that's just never been implemented at scale," Deckelbaum said.