The T15 soldering tip is made out of stainless steel at the body. The head is made out of copper with iron and chrome plating at the exterior. The head will also contain excess solder and other contaminants from use so the user should also be aware of these during disposal. The leads are nickel, and the heater wire is Constantan. The heater is encapsulated in ceramic compound. and the plug is PBT with the terminal contacts being made out of nickel-plated phosphorus bronze.
Without knowing what the process the tip is being used for, it is best to dispose of expired tips by adhering to local ordinances for industrial waste.