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Occurrence and Production of Chlorine
Occurrence
In nature, chlorine is found mainly as the chloride ion, a component of the salt that is deposited in the earth or dissolved in the oceans - about 1.9% of the mass of seawater is chloride ions. Even higher concentrations of chloride are found in the Dead Sea and in underground brine deposits. Most chloride salts are soluble in water, thus, chloride-containing minerals are usually only found in abundance in dry climates or deep underground. Common chloride minerals include halite (sodium chloride), sylvite (potassium chloride), and carnallite (potassium magnesium chloride hexahydrate).
Industrially, elemental chlorine is usually produced by the electrolysis of sodium chloride dissolved in water. Along with chlorine, this chloralkali process yields hydrogen gas and sodium hydroxide, according to the chemical equation;
2NaCl + 2H2O Cl2 + H2 + 2NaOH