The ion exchange process relates to the interaction of various ionic species in aqueous solutions with adsorbent solid materials. This process is easily differentiated by the nature and morphology of the adsorbent material which in most cases is either a versatile and dynamic polymer matrix or an inorganic structure containing exchangeable various functional groups. The ion exchange resins are generally made by cross-linked copolymers of styrene (vinyl benzene), with divinyl benzene.
The ion exchange process is a reversible interchange and stoichiometric sorption chemical process in which various unwanted ions in solution are exchanged for other ions with a similar charge but of different species attached to an insoluble resin. It is actually a rate-controlled process which generally governed by diffusion in the solid phase or in the surrounding liquid film. These ion exchange resins generally come from naturally occurring inorganic zeolites or are synthetically produced.
Synthetic-type resins are mostly used nowadays because their characteristics can be tailored to specific applications. Organic or inorganic network structure with attached functional groups is found on an organic ion exchange resin that can exchange their mobile ions for ions of similar charge from the surrounding medium.
Each resin has a specific number of mobile ion sites that set the maximum quantity of exchanges per unit of resin. The resins of the exchangers are called cationic exchangers if they exchange positive ions and anionic if they exchange negative ions. The resins of the cation exchanger consist of acidic functional groups such as sulfonic, whereas anion exchange resins are often classified based on the nature of the functional group as a strong acid, weak acid, strong base, and weak base.
The character of the acidic or basic mostly relays on the degree of ionization of the functional groups, similar to the situation with soluble acids or bases. The ion exchange process is suitable for the purification of aqueous solutions using solid polymeric ion-exchange resin. It can possible the purification and separation of a variety of industrially and medicinally important chemicals by applying this process.
Principle of Ion exchange process
The synthetic resins in ion exchangers are treated with the ions of the solution and exchanged with accumulated ions with the same electrical charge on the resin. The ion exchanger consists of the column where resin is mixed into a container of solution and then removed for further treatment. These resins are granular substances that have in their molecular structure acidic or basic radicals that can be exchanged easily.
The negative and positive ions fixed on these radicals are generally replaced by ions of the same sign in the sample solution in the liquid in contact with them. This process cannot be completed without the deterioration and changing of the total number of ions in the liquid before the exchange. There exists two type of resin namely the resins of the gel type and those of the macroporous or loosely cross-linked type. It will be possible to exchange ions easily if the resin is supersaturated with a loosely held solution. It is used sulfonated polystyrene beds for water softening that have been supersaturated with sodium.
Various unwanted ions attach to the resin beads and release the loosely contained solution into the water. It should be replenished or recharged after the beds get saturated. The brine solution can be used for flushing purposes. The regeneration work needs backwash, salt absorption, slow flush (replacement), and fast flush.
Applications of the ion exchange process
The ion exchange process is very much used in the laboratory, the food and beverage industry, hydrometallurgy, chemical, petrochemical, pharmaceutical technology, sugar and sweetener production, ground- and potable-water treatment, metals finishing, nuclear, softening, industrial water treatment, semiconductor, power, and many other industries. It is very important for the routine analysis of amino acid mixtures. The products of hydrolysis of nucleic acids can be analyzed by this technique.
It is possible to analyze the structures of complex biological materials by helping this ion exchange process. The lanthanoid compounds are separated on columns of cation-exchange resin. The various metals form negatively charged chloride complexes that can be held by anion-exchange resins carrying quaternary ammonium groups.
There are various trace metals from seawater can be collected by applying chelating resins. Ion exchangers are widely used for water softening, water purification, and water decontamination process. This ion exchange process is very essential in household filters along with reverse osmosis (RO) membranes to produce soft water for the benefit of laundry detergents, soaps, and water heaters.
The plutonium-uranium extraction process can be driven by this process. Two chemicals namely zirconium and hafnium can be separated easily by this process. The radioactive wastes can be reprocessed by this process. The resin of this process is also used in the chloralkali process, fuel cells, and vanadium redox batteries. The resin of this process helps to determine the swelling capacity of swelling or expansive clay such as montmorillonite, which can be used to “capture” pollutants and charged ions. This process helps to create the guiding layer of a higher index of refraction.
References
Nasef, M. M., & Ujang, Z. (2012). Introduction to ion exchange processes. Ion Exchange Technology I: Theory and Materials, 1-39.
