DI Water Systems

Deionization (DI) / Ion exchange

This process removes ions from water, usually RO water, with the use of synthetic resins. The ions are removed from the water through a series of chemical reactions. These reactions occur as the water passes through the ion exchange resin beads. Gradually, all unwanted ions are replaced by hydrogen and hydroxyl ions which combine to form pure water measuring at 1-15meg ohm. 

Our high-quality water systems are manufactured in the US to the most demanding Standards. Avidity holds all spare parts and consumables for local delivery.  Our local teams of expert water engineers can carry out your routine servicing and maintenance.  Complete turnkey packages for installation, commissioning and on-going service are available here.

Type 2 water is used for:

  • General laboratory applications requiring higher ionic purity
  • Buffer make up
  • Media production
  • Sample dilution and reagent preparation
  • General Chemistry

Removes:      Dissolved inorganic ions

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How does Deionization (DI) work?

Deionization is a chemical process which uses specially manufactured ion-exchange resins which exchange hydrogen ion and hydroxide ion for dissolved minerals, which then recombine to form water. Deionized water has typically had its mineral ions removed, such as cations from sodium, calcium, iron, and copper, and anions such as chloride and sulfate.

Laboratory deionizers incorporate mixed bed cartridges of ion exchange resins that are discarded. Deionization functions by exchanging hydrogen ions for cationic contaminants and hydroxyl ions for anionic contaminants in the feed water. The ion exchange resin beds are made up of tiny spherically shaped bead through which the water passes. After a period of time, cations and anions will have replaced all the hydrogen and hydroxyl in the resins and the cartridges will need to be replaced.

How does Electrodeionization (EDI) work?

RO/EDI systems feature an EDI module that consists of ion exchange resins used in single beds for enhanced water purification. Microbiological analysis of product water shows a high decrease in proliferation of bacteria due to the high pH swing between the 2 cells and direct contact of resin and electrodes. Furthermore, an intermediate pH shift has a positive effect on the separation of SiO2 (Silicon Dioxide) and CO2 (Carbon Dioxide). We also see a remarkable reduction in the number of bacteria with high colony forming unit (CFU) counts from the feed water, as electrodes in the water make it unsuitable for bacteria to live.

EDI’s Clear Advantage Is Continuous Operation

EDI Technology is designed to have the module continually regenerate itself, without any acids or alkalis. This technology is a cost effective way to ensure pure water when you need it and also benefits the environment because of less required consumables. The combination of RO membranes and the EDI module offers minimal downtime which means fewer process interruptions for you.

Deionization uses synthetic ion-exchange resins to chemically remove ions from feed water. As the water passes through the ion exchange resin beads, hydrogen and hydroxide ions are chemically exchanged with dissolved minerals to form water.

Deionization resin beds or columns are made from cation-exchange resins and anion-exchange resins either in separate beds or packaged together. Different technologies are referred to as co-current, counter-current and mixed bed. Most commercial resins are made of polystyrene sulfonate and oppositely charged ion exchanging sites are introduced after polymerization. Cation-exchange media use sulfonic acid groups to exchange a hydrogen ion for any cations they encounter (e.g., Na+, Ca++, Al+++) and anion-exchange resins use quaternary amino groups such as polyAPTAC to exchange a hydroxyl for any anions (e.g., Cl-, NO3-, SO4–). When the hydrogen ion from the cation exchanger unites with the hydroxyl ion of the anion exchanger pure water is formed.

Once all of the ion exchange sites on the resin have been filled by contaminants in the water, the resin will become exhausted. Resins may be regenerated by chemically rinsing in strong acid and bases to recharge the beads. Regeneration may be carried out when large cylinders of resin are used in industrial applications. In laboratory water systems, cartridges are discarded once exhausted. Choosing a water system with large capacity, longer lasting consumables will impact greatly on running costs.

Deionization is the only technology which produces the resistivity requirement for Type 1 ultrapure reagent grade water. The electrical resistivity of ultra-pure water is 18.2 MΩ-cm. This low conductivity can only be achieved with water dissociation equilibrium which requires the production of H+ and OH− ions in the presence of dissolved monatomic gases.