read that and then tell me is that what you want for cornwall.
I remember playing on a beach in Cornwall & getting covered with oil from the Torrey Canyon, I also saw the dead & dying seagulls covered in oil.
Cornwall is already battle scarred by millenia of mining metals such as tin, copper, arsenic, and from china clay (kaolinite) extraction.
The lithium extraction so far proposed is from hydrothermal fluids that have picked up lithium from pegmatites & so is subsurface extraction using wellheads, together with geothermal heat recovery.
We already have copper mines scarring areas of Cornwall, North Wales & the Lake District.
REE deposits in the UK include the Loch Loyal syenite complex which would devastate a beautiful area, the Mourne Mountains in NI have REEs too in alluvial deposits.
Remember too that REEs are already used as catalysts in petroleum refining & that switching from one use to another is possible.