How precious they are is partly dependant on their age. If they were originally wrought before July 1945 (first atomic explosion) could be in great demand by laboratories who measure tiny amounts of radiation. This goes for mild steel, very old lead pipe etc.

If you cannot find such a laboratory try either HMS Warrior at Portsmouth, SS Great Britain in Bristol – they are made of the stuff. You might be able to sell it to a Boat builder. Wrought Iron is nearly inert in sea water. I think Warriors plates have lost less that 1/16” in over 100 years. 

The stuff is also very tolerant of the harsh conditions inside a fire box. My mother used to cook on a kitchen range made about 18 and ‘how is your father?’ In the mid 1960s the fire bars gave way. The local ironmonger looked sadly at the remains and said ‘we still sell these but they are expensive as they are wrought Iron not the cheap cast iron ones like this’ Dad paid 10/- (Shillings in real money) When he sold the house some 12 years later they as good as new but the new owner’s scrapped the whole thing.’