Chelating resin
Encyclopedia
Chelating resins also known as specific exchangers or chelating sorbents are usually perceived as a subgroup of ion exchange resin
s.
Chelating resins were developed to obtain higher selectivies of at least one particular counter-ion species. The interaction of functional group (ligand
) of chelating resin and metal (in form of cation or oxoanion) is selective with respect to the nature of the metal. The theory behind the choice of functional group is explained as such: An ion that forms strong complexes with, or is precipitated by, a certain reagent should thus be preferred by a resin into which this reagent has been incorporated.
However, in the case of chelating resins counter ions are bound to resin by coordinate covalent bond
or by its combination with electrostatic interactions. While the case of ion exchange
, electrostatic force between oppositely charged functional group and ion in solution plays the main role.
Chelating resins have the same bead form and polymer matrix as usual ion exchangers. They are mainly based on crosslinked
polystyrene
.
Typical functional groups of chelating resins are:
Ion exchange resin
An ion-exchange resin or ion-exchange polymer is an insoluble matrix normally in the form of small beads, usually white or yellowish, fabricated from an organic polymer substrate. The material has highly developed structure of pores on the surface of which are sites with easily trapped and...
s.
Chelating resins were developed to obtain higher selectivies of at least one particular counter-ion species. The interaction of functional group (ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
) of chelating resin and metal (in form of cation or oxoanion) is selective with respect to the nature of the metal. The theory behind the choice of functional group is explained as such: An ion that forms strong complexes with, or is precipitated by, a certain reagent should thus be preferred by a resin into which this reagent has been incorporated.
However, in the case of chelating resins counter ions are bound to resin by coordinate covalent bond
Coordinate covalent bond
A dipolar bond, also known as dative covalent bond or coordinate bond is a kind of 2-centre, 2-electron covalent bond in which the two electrons derive from the same atom. Typically, a dipolar bond is formed when a Lewis base donates a pair of electrons to a Lewis acid. This description of bonding...
or by its combination with electrostatic interactions. While the case of ion exchange
Ion exchange
Ion exchange is an exchange of ions between two electrolytes or between an electrolyte solution and a complex. In most cases the term is used to denote the processes of purification, separation, and decontamination of aqueous and other ion-containing solutions with solid polymeric or mineralic 'ion...
, electrostatic force between oppositely charged functional group and ion in solution plays the main role.
Chelating resins have the same bead form and polymer matrix as usual ion exchangers. They are mainly based on crosslinked
Cross-link
Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds. "Polymer chains" can refer to synthetic polymers or natural polymers . When the term "cross-linking" is used in the synthetic polymer science field, it usually refers to the use of...
polystyrene
Polystyrene
Polystyrene ) also known as Thermocole, abbreviated following ISO Standard PS, is an aromatic polymer made from the monomer styrene, a liquid hydrocarbon that is manufactured from petroleum by the chemical industry...
.
Typical functional groups of chelating resins are:
- iminodiacetic acidIminodiacetic acidIminodiacetic acid, HN2, often abbreviated to IDA, is an dicarboxylic acid amine. The iminodiacetate anion can act as a tridentate ligand to form a metal complex with two, fused, five membered chelate rings...
- aminophosphonic
- thioureaThioureaThiourea is an organosulfur compound of with the formula SC2 . It is structurally similar to urea, except that the oxygen atom is replaced by a sulfur atom, but the properties of urea and thiourea differ significantly. Thiourea is a reagent in organic synthesis. "Thioureas" refers to a broad...
- 2-picolylamine