How long does it take peanut dust to settle from the air after eating roasted or shelled peanuts from an open can? Will an air purifier clean the air?

A physics question! How big is the room (volume), what is air flow in the room, and what is the weight of the particulates(peanut dust)? This is a real question of applied physics and not an easy answer. Hepa filters, especially hospital grade ones do a good job of air clearance.