Hairdryers might be suitable for reuse through a local reuse network such as Freecycle or Freegle. There are now a large number of reuse groups on Facebook. If they are broken they can be taken to your nearest Repair Café where a volunteer will try and fix it for a donation.
Otherwise these can be taken to a local Household Recycling Centre and included in the small electrical appliances container. For sites without a small electrical appliance container these can be included in the scrap metal container.