The concept of chelation is based on the observation that when a certain amino acid complex called EDTA (ethylene-diamond-tetra-acetic acid) comes in contact with certain positively charged metals and other substances such as lead, iron, copper, calcium, magnesium, zinc, plutonium and manganese, it grabs them (hence the chele or claw) and removes them.
EDTA is a synthetic amino acid first used in the 1940s for treatment of heavy metal poisoning.