My reasoning was to note that the Magrathea collateral is pushing "low energy" to make the connection. I am NOT saying I KNOW that this how they are doing it. It is because this is a "mature market" in terms of well established players who are doing this with lime and salt ponds that I was wondering "Has anything changed that would convince a VC (or Angel) to fund a new magnesium producer? What would have to be true in order to have a value proposition that would convince someone they could succeed against the established players?
And so I go off and search various "research news" web sites to see if there is any news on Magnesium extraction. If they are not using this research then I would be skeptical of their success given the existing market is well established and making a new venture using existing techniques is pretty capital intensive.
Then you neutralize the magnesium hydroxide with hydrochloric acid to make Magnesium chloride and do molten salt electrolysis on it to make pure magnesium and chlorine.
Recently most magnesium comes from China. They mine ore, throw it in a coal-fired furnace along with some reducing agents, then collect pure magnesium vapor. This process is more labor and energy intensive, but has significantly less CAPEX. Works for China.
Chlor-alkali is more expensive than lime and the back-end electrolysis is more expensive than thermal reduction. So I'd be skeptical they are going to lower costs without some kind of CAPEX reducing magic for molten salt electrolysis.