If it was once live, but left in air for a year, it needs to be cleaned of all old organic debris or you risk having a mini (or maxi) cycle when the dead/decayed material hits your tank. There are threads about acid washing, I've never tried it, but something similar would be needed.
If you have it in a barrel, keep the water moving (throw a powerhead in there) and control the temperature and keep specific gravity maintained (top off evaporation) and let it "cook" for quite some time, so the cycle can happen, and then once complete it will begin to become live rock again, and be safe to go into your system.
There are articles in the stickies on the top that discuss both if these methods.