There are number of ligands capable of binding metal ions through multiple sites, usually because they have lone pairs on more than one atom. Ligands that bind via more than one atom are often termed chelating ligands. The organic moiety that can trap or encapsulate the metal ion, forming coordinate bond through two or more atoms, to form a chelate is known as chelating agent/ligand. So, ‘‘chelate’’ denotes a complex between a metal and a chelating agent. A chelating agent can be chemically anchored on various inorganic polymeric solid supports to form ‘‘chelating resin’’. The ligand/agent attached to chelating resin makes it specific and selective for extraction of a particular metal ion (Fig. 14.15).

Various solid supports that are used for scavenging of metal ion are: Chelamine, Silica gel, Amberlite, XAD, Polyurethane foam, Polyacrylonitrile, and Activated Carbon.

The tremendous amount of biomass which is produced after phytoextraction is rich source of heavy metals drawn from the soil which are otherwise the major environmental concern. This biomass is digested and a particular metal specific chelating resin, which possesses high selectivity to the targeted metal ion in a par­ticular pH — range, is used for separation of metal ion. An assortment of novel metal specific chelating resin has been designed which can be easily recovered and reused several times making the process environmentally benign and green (Table 14.2).

Extraction of metal ions from biomass using specifically designed chelating resin has numerous advantages [26]:

• Selective extraction of metal ions is possible by using a chelating resin having multidentate ligand as it possesses high selectivity to the targeted metal ion.

• The chelating sorbent method is an economical method since it uses only a small amount of resin and is free from difficult phase separation and extraction solvent.

• As the target ion specific chelating agent is enriched on solid phase, even ppb level concentrations can also be extracted.

• The chelating resin can be recycled and reused several times as they can be easily recovered merely by filtration and have high physical and chemical stability.