Demineralization is essentially removing all the minerals that can be found in natural water. This process is usually done when the water will be used for chemical processes and the minerals present may interfere with the other chemicals. All the mineral and salt ions which is responsible for hardness of water are removed from the raw water, such as Calcium, Magnesium, Sodium, Chloride, Sulphate, Nitrate and Bicarbonate.
In the De-Mineralization process Ion exchange resins play a main role.
The following ions are widely found in raw waters:
Calcium (Ca2+) Chloride (Cl-)
Magnesium (Mg2+) Bicarbonate (HCO3-)
Sodium (Na+) Nitrate (NO3-)
Potassium (K+) Carbonate (CO32-)
Ion Exchange Resins :
There are two basic types of resin – cation-exchange and anion-exchange resins. Cation exchange resins will release Hydrogen (H+) ions or other positively charged ions in exchange for impurity cations present in the water. Anion exchange resins will release hydroxyl (OH-) ions or other negatively charged ions in exchange for impurity anions present in the water.
The application of ion-exchange to water treatment and purification. There are three ways in which ion-exchange technology can be used in water treatment and purification:
First, cation-exchange resins alone can be employed to soften water by base exchange; secondly, anion-exchange resins alone can be used for organic scavenging or nitrate removal; and thirdly, combinations of cation-exchange and anion-exchange resins can be used to remove virtually all the ionic impurities present in the feed water, a process known as deionization. Water deionizers purification process results in water of exceptionally high quality.
This water is also called soft water because all the hardness is removed by the de-mineralization process.
Generally soft water is used in boilers to produce the stem because it does not create the problem of scaling in the boilers. Soft water is also used to feed purified water plant.
All chemistic and beauty products have to be made with demineralized water for this reason. With the demineralization process, the water is “softened” replacing the undesired minerals with different salts (NaCl).
Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use and produced using DM water. To prepare the purified water, DM water is passed through Reverse Osmosis membrane and ultra violet light. Reverse Osmosis removes the soluble impurities from the water by passing water through its membrane having pore size 0.0003µ.
Ultra violet removes microbes from water making it free from microbial contamination.
Purified water is also used in the pharmaceutical industry. Water of this grade is widely used as a raw material, ingredient, and solvent in the processing, formulation, and manufacture of pharmaceutical products, active pharmaceutical ingredients (APIs) and intermediates, compendial articles, and analytical reagents.
Purified water is also use to produce water for injection. It is distilled in multi-column distillation plant and collect by the condensation process.
Both DM water and purified water has their own specification to be passed their quality. DM water should be pass the hardness and pH test only while purified water has various parameters like description, conductivity, pH, heavy metal, hardness, nitrate, sulfate, iron, residue on evaporation, microbial limit test etc.