Deionized water, often referred to as DI water, is a purified water created by removing nearly all mineral ions like sodium, calcium, iron, and copper. This process results in water exceptionally free of charged particles, unlike tap water which contains various dissolved salts and minerals. The absence of these ionic impurities makes deionized water suitable for applications where even trace amounts of minerals could interfere with processes or product quality.
How Deionized Water is Produced
Deionization primarily relies on ion exchange. This method involves passing water through specialized synthetic resins. As water flows over these beads, dissolved ions are chemically exchanged for hydrogen (H+) and hydroxyl (OH-) ions. For instance, positively charged ions (cations) like calcium and magnesium are swapped for hydrogen ions by cation exchange resins. Negatively charged ions (anions) such as chloride and sulfate are exchanged for hydroxyl ions by anion exchange resins.
The hydrogen and hydroxyl ions then combine to form water (H2O), effectively removing impurities. This process can use separate beds for cation and anion exchange or a mixed bed. While ion exchange is the primary method, deionization systems often incorporate pre-filtration steps, like reverse osmosis, to remove organic matter and particulates before ion exchange.
Unique Characteristics of Deionized Water
Deionized water is defined by its extreme purity, lacking dissolved minerals and ions. This gives it a very high electrical resistivity, meaning it is a poor conductor of electricity. Pure deionized water can achieve a resistivity of up to 18.2 megohms-centimeter at 25°C. This contrasts sharply with tap water, which contains numerous conductive ions.
The removal of dissolved solids ensures deionized water leaves virtually no residue upon evaporation. Its purity also means it acts as a “true water blank,” readily assuming the chemical properties of whatever substances are introduced. This unique solvent capability, combined with its non-conductive nature, makes it invaluable in sensitive applications where mineral contamination or electrical conductivity would be problematic.
Common Applications of Deionized Water
Deionized water’s purity makes it indispensable across many industries and scientific fields.
Laboratory Use
In laboratories, it is used for preparing solutions, cleaning glassware, and conducting experiments where trace contaminants could skew results. It ensures accuracy in sensitive analytical procedures, such as High-Performance Liquid Chromatography (HPLC).
Industrial Applications
Industrially, deionized water is important in electronics manufacturing, particularly for producing semiconductors and circuit boards, as it prevents mineral deposits that could cause electrical failures. It is also employed in automotive care for battery water and in cooling systems to prevent scale buildup and corrosion.
Medical and Pharmaceutical Use
Medical and pharmaceutical sectors use DI water for preparing medications, sterilizing instruments, and manufacturing medical devices, ensuring product safety and preventing contamination.
Power Generation
Power plants use deionized water in steam generation to protect equipment from mineral scaling.
Important Usage Information
Despite its purity, deionized water is not recommended for regular drinking. While technically safe, it lacks essential minerals like calcium and magnesium found in tap water, which are beneficial for human health. Consuming it exclusively can lead to electrolyte imbalances over time.
Deionized water tends to re-ionize by absorbing substances from its environment. For instance, it readily absorbs carbon dioxide from the air, which can lower its pH and increase its conductivity. This “hunger” for ions also means it can be slightly corrosive, leaching minerals from pipes or containers it contacts. Therefore, proper storage and handling are important to maintain its purity and prevent equipment damage.