Meaning it could be decades before there is any meaningful production for this source. Or "never, because it turned out that the cost of extracting 'em from coal ash was 10X higher".
The variation of interest with coal ash is using REE profits to offset the costs of dealing with the coal ash specifics .. which need to be dealt with in any case in order to ensure purity of water supplies, etc.
The US DoE put up ~ $18 million (US) in April 2024 to develop pilots which are already running that will provide feedback for tuning second generation circuits.
The full paper: https://link.springer.com/article/10.1007/s40789-024-00710-z
The DoE critical minerals supply funding context: https://netl.doe.gov/node/13632
2022 policy launch: https://www.whitehouse.gov/briefing-room/statements-releases...
2022 USGS Critical minerals for US list: https://www.usgs.gov/news/national-news-release/us-geologica...