This is going to be a quick one on zinc and iron and how it helped.
The same thing happened with ice, she was chewing on ice constantly when she wasn't chewing on metal! She would hold an ice cube in her hand and just eat it like it was a cookie! Sierra's hand would turn bright red from holding the ice and it didn't seem to bother her. So after the zinc stopped the metal chewing, we focussed on the ice. The doctor gave us iron to give to her and she stopped chewing on ice right away!
Now I have always known that ice chewing could be a difficiency in iron but we were giving her iron in a multivitamin so we thought that something else was causing it. We just were not giving her enough the doctor said. He had done blood work and said she was low in these minerals even though she was taking the multivitamins! Eating or chewing on non food items is most often a sign of some vitamin or mineral deficiency.