Thanks for pointing that out; my neighbour, a material scientist at Cambridge, made that clear to me as well when he explained that steel quality decreases with every iteration of recycling: it needs more and more energy (and resources) to keep a recirculating mass of steel in a circular economy at a certain quality. Therefore, a certain amount of mining would always be needed, with more and more energy effort, too, which is a contradiction to the circular economy paradigm on a planet with finite resources. Life is a struggle against entropy.

Nevertheless, for some resources, I would hope that there is a regeneration potential of the Earth; so, theoretically, a circular economy could work for some aspects as long as the deteriorating mass is compensated by the earth's regeneration. Since that might not be very much, the total mass of recirculating goods would have to be small, too. Frugality and thrift comes into my kind as well as the need for keeping things in use for a long time based on long-lasting designs.

Should you be interested, I tried to articulate my thoughts around that in https://medium.com/@peter-wurmsdobler/prosperity-within-material-boundaries-ff0ed36d5111