**5.2. Chelation**

It refers to the process in which a chelating agent binds to the metal ion at more than one place at a time in order to form a ring structure and the complex is known as chelate. Mostly polydentate ligands participate in the reaction to form stable structures by multiple bonding. An increase in binding sites of the ligand increases the stability of the structure. Chelates are more stable than complexes because of multiple binding with the metal ion in more than one place. Rice straw was used as a potential biosorbent for the removal of Cd (II) from the effluent. The biosorbed Cd (II) chelates with the functional groups such as C=C, C–O, and O–H and carboxylic acids which are present on the surface of the biosorbent [44]. A similar mechanism of biosorption was reported in the removal of Cr (III) and Cu (II) by carboxyl and hydroxyl groups present on the surface of soybean meal waste [45].
