Ion Exchange is defined as a reversible exchange of ions between a solid (resin) and a liquid (containing dissolved ionized solids or salts) in which there is no apparent change in the structure of the solids. Deionization is the process of removing the dissolved ionized solids from water by ion exchange. The major portions of total dissolved solids (TDS) are mineral salts, such as calcium bicarbonate, magnesium sulfate, and sodium chloride. Mineral salts are composed of cations and anions. Since deionization requires the removal of all ions, both the negatively charged anions and the positively charged cations, then materials capable of attracting both are required. These materials are known as cation and anion exchange resins.

Deionizers are fixed bed systems in which the ions exchange resins are contained in pressure tanks. The water to be deionized is forced through the resins. The cation and anion exchange resins have a specific capacity to remove a known amount of ionizable solids. After a service run the resins become exhausted and are unable to remove additional ions. When the resins are exhausted, they must be regenerated with a strong acid and a strong base to restore their ion exchange capacity. Cation resin is typically regenerated with hydrochloric or sulfuric acid. Anion resin is normally regenerated with sodium hydroxide, although potassium hydroxide can be used under certain circumstances.

Two-bed model deionizers have two separate resin containing vessels, the first being a cation unit followed by an anion unit. Cation resin in the hydrogen form (as it will be after regeneration with a strong acid) collects all of the positively charged cations such as calcium, magnesium, sodium and potassium, and exchanges them for hydrogen. The discharge from the cation tank is very low pH because the hydrogen combines with the negatively charged anions in the water to form acids, such as hydrochloric, sulfuric and nitric. There will be a small amount of sodium, which will not be exchanged, and the sodium "leakage" will determine the final water quality.

Two types of two-bed units are available. Strong base anion resin units remove all anions including silica and carbon dioxide. They typically produce deionized water with a pH greater then 7, and the amount of silica remaining is usually less than 0.2 ppm.

Weak base anion units are used when removal of silica and carbon dioxide are not required. Weak base anion resin has a higher capacity and lower regeneration consumption. Since they do not remove carbon dioxide, they typically produce deionized water with a pH lower then 7.

Mixed beds contain intimately mixed cation and anion resin in a predetermined ratio that produces extremely high quality water. Silica and carbon dioxide removal are usually accomplished by the use of strong base resins. Mixed bed unit pH is typically 7.0 before the water is exposed to the atmosphere because of the almost complete deionization that occurs.

The quality or degree of deionization is generally expressed in terms of specific resistance (ohms or specific conductance-mhos). Ionized material in water will conduct electricity. The more ions there are in the water, the greater conductivity and less resistance. When ions are removed, resistance goes up, and therefore the water quality has been improved.

In summary, you are given "tanks" by the water conditioning company. These tanks are plumbed into the Tomahawk system and remove the hardness of the water. You will be able to use the tanks until they are exhausted. They are considered exhausted when they are just about 50 MicroMhos of conductivity. The Tomahawk system water quality control box monitors this. When the tanks are exhausted simply exchange them with a fresh set of tanks and purge the system for about a minute. Now you are ready to clean with spot free deionized water.

• What size tanks do I need

• How long will the tanks last?

• How much do the tanks cost?

• Cost of using spot free water