The Basics of Water Demineralization

Demineralization is the removal of dissolved minerals that form salts when water is evaporated. These salts have corrosive properties and must be removed for industrial processes so that they don’t damage equipment, such as high-pressure boilers. In ion exchange demineralization applications, salts are replaced with hydrogen and hydroxide to form pure water.

Water from various sources will have diverse concentrations of minerals. Rain water has nearly no minerals, whereas sea water has very high mineral content. The amount of minerals in water can be measured by assessing the amount of total dissolved solids as well as the conductivity of the water.

Demineralization systems are designed to reduce mineral content from water. Similar to softening, in ion exchange demineralization processes, cation resins are used for the removal of cations, and anion resins are used for the removal of anions.

However, in demineralization ion exchange systems, ion exchange resins will remove all mineral salts, except for traces of sodium and colloidal (undissolved) silica. Typical cations targeted for removal are calcium (Ca++), Magnesium (Mg++), Sodium (Na+), Potassium (K+) and Iron (Fe++). Typical anions targeted for removal are Bicarbonate (HCO₃-) Chloride (Cl-), Sulfate (SO₄--), Nitrate (NO₃-) and Silica SiO₂).

The performance of demineralizer systems is dependent on influent water chemistry, system design (co-flow or counter-flow), type of resin installed and regenerant type and concentration.