Welcome to Backyard Chickens! You can give them discarded egg shells as long as they don't resemble egg shells whatsoever or they will start egg eating habits. I agree with the post above. They can't replace oyster shell.
Yes, you should heat in oven or microwave to kill bacteria. I crush them with a mallet & then add them to their oyster shell. They shouldn't replace oyster shell.
There really isn't any need to sterilize them or even dry them if you are just giving them right back. Some chickens have been known to eat eggs and their shells from time to time and they don't seem to be dieing from them yet to solve that problem. Much to the dismay of their owners who then have to deter them from that habit. If you are going to store them then drying them is in order.
I put them in my CI in the oven on 350 for about 20 min. Then let them cool. I put them in a Ziploc bag, crushed, then put them in the freezer until I get some more. Good idea? Or should I have done it differently?
My ladies are not laying yet. We buy organic vegetarian feed eggs, are these shells okay to give AND at what point should I start giving shells for the extra calcium? Thanks in advance