Water Education - Water Quality

The Methods for the Removal of Ionic Impurities from Water

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Since many ions interfere with the beneficial uses of water, a number of methods have been developed for the reduction or substantial removal of ionic impurities from water.

There are a number of ways in which dissolved ionic impurities in the water may be reduced or substantially removed:

  • distillation,
  • precipitation and separation,
  • ion exchange, and
  • membrane separation.

Explain Ion

An ion is an electrically charged atom or group of atoms. The electrical charge of an ion with a single nucleus is due to the gain or loss of one or more electrons. Several of these simple ions may combine into groups, which then have a charge which is the sum of the charges of the sample ions in the group. The loss or gain occurs during chemical reactions in which electrons are transferred from one atom to another.

Note the change in the mane of the fluorine atom to fluoride ion. Most ions with positive or plus charges bear the same name as their corresponding atoms. But, most negative ions (when derived from single atoms) have the ending -ide added to the root of the word for the corresponding element. For example, fluoride, bromide, iodide, and sulfide ions.

Thus, ions have properties quite different from their parent atoms. Sodium is a silver-white alkaline metallic element with a waxlike consistency. Fluorine is a corrosive greenish-yellow gas. When combined through a chemical reaction, their ions result in a white crystalline substance of much the same appearance as common salt, except that it is more of a powdered consistency.

In many compounds the ions are equally attracted to each other in all directions. While there is no pairing of ions as such, there is one positive ion for each negative ion. In the case of sodium fluoride, this means one sodium ion for each fluoride ion.


The arrangements of ions

  • Negatively charged ions
  • Positively charged ions

The above sketch gives an indication of one of many types of arrangements of ions attracted in all directions to ions of the opposite charge.

From the various examples cited on the last few pages, it is obvious that atoms have varying amounts of electrons in their outer shells which can be transferred or shared.