This is certainly a safe method, the absorbers being out side of the mine.
It would most likely be expensive. Absorber beds would be large in volume and expensive to purchase. Rapid turnover of the air in a mine is the key in mine safety. So these absorber beds would have to be huge to handle the large volumes of air moving through the mine.
There would need to at least two banks of absorber beds because one would have to be in service while the other was being regenerated.
Regeneration of absorbers usually requires a great deal of energy because they typically are heated in order to get the absorber to release the captured gas.
Considering the cost of purchasing this technology and operating it, I don’t see this being a cost effective proposition.
But then the whole Green House Gas Global Warming thing doesn’t make any sense anyway.
The thing with all these enviro-driven "conservation" projects is that, if they made sense, somebody would've already found a way to do them.
The mere fact that the federal government -- the sponsor of last resort for bad ideas -- has to undertake this project is proof positive that it makes no sense.