The Collaborative International Dictionary of English v.0.48:

chelation \chelation\ n.
   the process of removing a heavy metal from a solution by
   means of a chelate; as (Med.) the treatment of lead or
   mercury poisoning by adding a chelating agent to the blood.
   [WordNet 1.5 +PJC]

   2. the process of forming a ring by forming one or more
      hydrogen bonds.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

chelation
    n 1: (medicine) the process of removing a heavy metal from the
         bloodstream by means of a chelate as in treating lead or
         mercury poisoning
    2: the process of forming a ring by forming one or more hydrogen
       bonds