Sodium is a chemical element with symbol Na (from Latin natrium) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table, because it has a single electron in its outer shell that it readily donates, creating a positively charged atom — the Na+ cation. Its only stable isotope is 23Na. The free metal does not occur in nature, but must be prepared from compounds. Sodium is the sixth most abundant element in the Earth’s crust, and exists in numerous minerals such as feldspars, sodalite and rock salt (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth’s minerals over aeons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.
Sodium was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Among many other useful sodium compounds, sodium hydroxide (lye) is used in soap manufacture, and sodium chloride (edible salt) is a de-icing agent and a nutrient for animals including humans.
Metallic sodium has few commercial uses, mostly as a intermediate to other useful compounds. Sodium reacts violently with water to form sodium and hydroxide ions plus hydrogen gas.
Sodium ions are well removed by hydrogen form strong acid cation resins. Hydrogen ions release in exchange for sodium are then neutralized by hydroxides released by the strong base anion resin that follows. .
Potassium form strong acid cation resin can be used to exchange for sodium ions in neutral waters, thus enriching the water with potassium ions.