A sustainability study on the lithium supply chain that assessed fuel use, power sources and energy intensity, found that hard-rock lithium will be responsible for 10 million tonnes of CO2 by 2030, with brine responsible for around 2.5Mt.

The consultancy blamed the more energy-intensive nature of hard-rock mining, along with the requirement for shipping concentrate to China for refining, for the "clear contrast" in emissions intensity.

It also pointed to the high emissions intensity of refining concentrate to lithium carbonate or hydroxide, in part driven by China's power grid mix and reliance on coal.

Battery Chemicals analyst Alex Grant, chief executive of Jade Cove Partners, noted in January that the CO2 intensity of battery quality LiOH•H2O (lithium hydroxide) products was seven times higher in those made from spodumene resources in comparison to brine.

"If the European market and industry professionals would like to see the industry move towards the final frontier of deep decarbonisation, then this is bad news," wrote Grant.

Lithium sourced from hard-rock spodumene sources requires an average 9t of CO2 for every tonne of refined lithium carbonate equivalent produced, nearly triple that of the average tonne of LCE from the brine sector, said Roskill in its paper.

This will increasingly be on investor's radar due to the growing importance of ESG (Environment, social & governance) factors, and "scrutiny of the lithium sector's sustainability is set to grow", warned Roskill.