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What Is Chlorite?

Treatment plants often use chlorites to cleanse water.
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  • Written By: Phil Riddel
  • Edited By: Jessica Seminara
  • Last Modified Date: 28 August 2014
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In the context of chemistry, chlorites are compounds containing the chlorite anion (ClO2-) and can be regarded as salts of chlorous acid (HClO2). The most commonly used of these is sodium chlorite (NaClO2). When dissolved in water it forms positively charged sodium cations (Na+) and negatively charged chlorite anions (ClO2-). It is mainly used for producing chlorine dioxide (ClO2), a yellowish brown, highly reactive gas that is employed in the paper industry for bleaching wood pulp, but is also an extremely effective biocide, due to its strong oxidizing properties.

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At high concentrations, chlorine dioxide is unstable and can react explosively with organic or combustible materials; it is therefore not normally stored or transported, but instead prepared at its place of use by the reaction of sodium or calcium chlorite with a strong acid. Chlorine dioxide dissolves in water to form chlorous acid, producing chlorite anions that are also powerful oxidizing agents. They are even more effective in killing microorganisms than chlorine, and because of this chlorine dioxide and chlorites are often used at water treatment plants to disinfect drinking water. These substances also have the advantages of not leaving a noticeable smell or taste, not reacting with organic material to produce harmful compounds such as chloroform, and being less corrosive to materials used to contain and transport water. In addition, chlorite and chlorine dioxide are helpful in sterilization of containers and surfaces in hospitals and in the food industry, and in water purification for hikers and campers, where a chlorite solution is mixed with an acid just prior adding it to the water.

Treatment of drinking water with chlorine dioxide leaves small amounts of chlorite ions in the water; however, this is not thought to pose any risk to health. Ingestion of relatively large amounts produces toxic effects: for example, it can react with hemoglobin, causing it to release oxygen less readily, but there is no clear evidence of any adverse health effects through normal exposure. Although it is possible for chlorites from water treatment or industrial sources to get into groundwater, due to their reactivity they break down quickly and do not accumulate in the environment.

Chlorite salts must be handled with care due to their oxidizing properties. They can form potentially explosive mixtures with other materials and react with acids to produce chlorine dioxide, with consequent risk of an explosion. For most purposes, chlorine dioxide and chlorites are used at very low concentrations

In the context of geology, chlorites are a group of mica-like silicate minerals. Although they do not contain chlorine, the names of both substances are derived from the Greek chloros, “green,” because of their usual greenish color. They are of variable composition, but generally contain magnesium, aluminum and iron as well as silicon and oxygen, and often form soft, flexible plate-like structures.

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