Catalyzes the ferrous insertion into protoporphyrin IX. 2 H(+) + heme b = Fe(2+) + protoporphyrin IX Binds 1 [2Fe-2S] cluster. Porphyrin-containing compound metabolism; protoheme biosynthesis; protoheme from protoporphyrin-IX: step 1/1. Homodimer. Belongs to the ferrochelatase family.