Steel is imported at much lower prices than the US steel mills will ever be able to deliver.
Rare earths was also sold by China at prices nobody else was able to compete (and China have majority of all known resources). But once major competitors went bankrupt and equipment was sold out (so that fast restarting of production became very costly), China made logical move, and impose export tariff for unprocessed R.E. metals. You still can purchase finished products, though.
Steel is much simpler product, but once you have mass production of plain carbon (construction) steel, you can afford to relatively economically produce most other varieties that may be necessary by current tech. Once you do not have mass production, your special steel may come close to silver by its price to be produced locally, and there is no guarantees that you'll be able to buy it anywhere else in a reasonable time.
And yes, coal (mostly coke that is produced from coal) is absolutely necessary to produce steel.
Solar batteries is another way to move pollution to China - learn how much energy is necessary to produce solar grade silicon from ores. And most of that energy is taken from coal plants in China. Also learn about energy density in sunlight at Earth sea level, real efficiency of currently produced commercial panels (not cutting edge prototypes priced at gold price by weight) and try to figure out which area you need to cover by panels (and exclude from agriculture) to replace one typical nuclear plant.