Pure, demineralized water, free from all soluble mineral salts is obtained by which of the following methods?

Pure, demineralized water is obtained by removing essentially all inorganic salts through ion exchange processes [1]. This method involves passing water through a cation exchange resin bed, which replaces dissolved cations with hydrogen ions (H+), and an anion exchange resin bed, which replaces anions with hydroxyl ions (OH-). These ions then combine to form pure water (H2O). Unlike Calgon's method or simple boiling, which primarily address water hardness (calcium and magnesium ions) without removing all soluble salts, the dual-bed or mixed-bed ion exchange process targets the near-total removal of all ionic mineral contaminants [1]. While microfiltration removes particulate matter, it is generally insufficient for removing dissolved mineral salts. Consequently, the sequential use of cation and anion exchange resins is the standard industrial method for producing high-purity deionized water.

Sources

1. [1] https://www.tn.gov/content/dam/tn/environment/water/ftc/references/study-guides/ftc_study-301_intro-wt-2.pdf