Ann: Green Iron grade concentrates produced using saline water, page-29

There have been some intelligent comments in regards to IP, lab testing and possible implementation issues,

Re "green steel".
I always thought that steel was an alloy of iron and carbon that requires cooking together at a high temperature to be achieved.
I can understand that the heat of the furnace can be supplied without burning coal (or any other fossil fuel) but I do not understand how hydrogen can replace the carbon that is "dissolved" in the iron to make steel or Is hydrogen also used to reduce CO2 to obtain unoxidized carbon? Seems somewhat uneconomic if that is the case when large deposits of essentially pure carbon are available in one form or another.
I also note that some steel plants have been producing steel with electric arc furnaces from fossil free electricity for decades, well prior to the current climate change religion appearing.

Grateful for any informed and intelligent answers.