This is one possibility of asteroid mining. An orbiting space station designed to capture and harvest these temporary moons at first, then if it works, capturing near Earth asteroids and even comets.
Granted, asteroid composition varies tremendously, for example 433 Eros, which is about the size of Manhattan, is believed to have more highly valuable platinum group metals than exist in all of Earth’s crust.
I was reading that the earth’s crust contains something like 17% iron while many asteroids are believed to consist of 70% or more iron.
Its not a terribly expensive metal on earth but lifting it to orbit is extremely expensive.