Ion exchange technologies are as varied as the terms used to describe them. Among these technologies are water softeners, dealkalizers, demineralizers and electrodeionization. Although this list is not exhaustive and the functioning of these technologies are not exactly the same, there are two points in common to each of them: the resin and the regenerant.
The exchange of ions takes place thanks to acid or basic radicals which are found in the molecular structure of the resin and which allow an exchange between those in the liquid to be treated and those on the resins.
What is a resin?
Resins are, for the most part, small plastic beads of a size varying between 0.3 and 1.2 mm. Even if to the naked eye, these beads appear to be smooth, they have a high porosity to increase the surface area for ion adhesion. During their manufacture, the resins are polarized to attract the desired ions.
Il existe plusieurs façons de catégoriser les types de résine. La plus répandue étant en fonction de sa charge électrique. On retrouve donc les résines anioniques et les résines cationiques. Les résines cationiques permettent l’extraction des ions chargés positivement comme le magnésium alors que les résines anioniques permettent l’extraction des ions chargés négativement comme le chlorure. Elles peuvent aussi être catégorisées en fonction des matériaux utilisés pour leur fabrication. Puisque la liste des matériaux est très longue, en voici quelques-uns des plus répandues :
- - Styrene divinylbenzene copolymer
- Acide méthacrylique divinylbenzène
- - Phenal-formaldehyde polymer
Regenerants
The regenerants are the products used to restore to the resins the ions necessary to perform the permutation. In other words, when the resin is exhausted, a regeneration cycle is started, and a concentrated solution is sent into the resin bed to restore its initial processing capacity. To give a simple example, let's look at the case of water softeners which, when the resin is exhausted, perform a salt regeneration cycle.
Hence, for the regeneration of anionic resin, salt that gives sodium ions can be used. For cationic resins, we can think of hydrochloric acid (HCl) as a regenerant.