Ion exchange resins for household applications
Depending on the quality of the drinking water available in a region, post-treatment may make sense for a variety of reasons. Here, the focus is on the hardness of the water in particular. Water hardness is defined as the sum of all alkaline earth ions, referred to as hardness components, whereby calcium represents the greatest problem. In conjunction with carbonate, which is also present in virtually all drinking water, it forms calcium carbonate, i.e. lime, which frequently crystallizes out as a white deposit and can result in scale formation in pipes and on fittings and heat transfer surfaces (heating, dishwashers, and washing machines, etc.) and, ultimately, damage to household installations and appliances. After all, coffee and tea taste significantly better when they are made using water with a low lime content.
Water with a high lime content is also referred to as hard water, and water with a low lime content as soft water. There are two methods based on ion exchange for reducing the hardness of water – complete softening and partial softening.
Both methods, and therefore both resin types, are also suitable for use in larger systems that can supply apartment buildings, residential complexes, remote settlements, and even entire villages and towns with soft drinking water.
All Lewatit® ion exchange resins used in this area were specially developed for application in the sphere of drinking water. Ion exchange filters like these also reliably retain lead, nickel, copper, and other metal ions that are hazardous to health.
In complete softening, the ions that cause hardness are generally exchanged for sodium. These systems can be regenerated with the aid of a special salt that is suitable for the purpose. The desired water hardness can be achieved by means of blending with untreated drinking water. Equipped with monodisperse, strongly acidic ion exchange resins, such softening systems exhibit only small drops in pressure, good exchange kinetics, and high long-term stability. In regions with especially hard drinking water in particular, substantial improvements in water quality can be achieved with this method. Our product Lewatit® S 1567 has proven to be successful in this area.
In addition to the outstanding properties already mentioned with regard to softening (effective regeneration, capacity, small hardness leakage), the resin can be disinfected effectively thanks to the way it is manufactured. This property increases the efficacy of disinfection by means of electrolytically produced chlorine during regeneration (in-situ disinfection).
With the partial softening method, only the carbonate hardness is removed. This is made possible by the special properties of the functional group that the the weak acidic resins employ. It ultimately produces carbonic acid and water if the exchangers are used in their hydrogen form. As a rule, the weakly acidic ion exchangers used for this are not regenerated in the household sector.
They are mostly used in easy-to-handle cartridge systems for private or professional use. Regeneration is possible in principle but requires the use of HCl or H2SO4. The major advantage of these weakly acidic resins is that they have a significantly higher capacity when compared with the strongly acidic resins used in complete softening.
Weak acid ion exchangers in H-form
Weakly acidic ion exchangers are used most frequently in their hydrogen form. It is in this form that they demonstrate the highest capacity relative to the volume used. Depending on the manufacturing process, these exchangers are available in white (Lewatit® S 8227 or Lewatit® S 8223) or yellow (Lewatit® CNP LF). The differing manufacturing process results in different properties that vary according to the area of application.
Doped weak acid ion exchangers
For some applications, it makes sense to dope the ion exchange resins with other cations to effect positive changes in the properties of the treated drinking water. For example, doping with magnesium can increase the magnesium content of the drinking water (Lewatit® S 8229 Mg).
Doping with sodium raises the pH value of the drinking water produced (Lewatit® S 8229). Doping with silver, which is permitted in some countries, has a positive effect on the microbiological contamination of the water (Lewatit® S 8229 plus Ag).
