If the Federal government is just buying, on the open market, an amount of coal comparable to how much would have been sold without government action, then it’s going to drive up the price of coal and increase the total amount of coal extracted. How much extra coal gets extracted depends on the supply and demand curves, and the amount of coal actually burned will almost certainly be less than in the world where the government didn’t act, but it does mean the environmental benefits of this plan will be significantly muted.
If the Federal government is just buying, on the open market, an amount of coal comparable to how much would have been sold without government action, then it’s going to drive up the price of coal and increase the total amount of coal extracted. How much extra coal gets extracted depends on the supply and demand curves, and the amount of coal actually burned will almost certainly be less than in the world where the government didn’t act, but it does mean the environmental benefits of this plan will be significantly muted.