Water Well Journal

July 2016

Water Well Journal

Issue link: https://read.dmtmag.com/i/692787

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Page 26 of 87

I n our world the reaction of "oxidation" can be found everywhere and the results can be beneficial in some cases and detrimental in others. Our knowledge and understand- ing of oxidation in groundwater can guide us in decisions such as design parameters, material selection, and operational controls. The original definition of oxidation provided by the scien- tific community was: "the union of a substance with oxygen." Over time with more study of various aspects of chemistry, it was determined the reaction of oxidation did not always in- volve the element oxygen and the definition was altered to its current form: "a chemical reaction in which an element or ion is increased in positive valence, losing electrons to an oxidiz- ing agent." To consider the action of transferring electrons, scientists established the "oxidation state" of known elements. There- fore, as elements reacted with each other and electrons were transferred, the oxidation state of the elements would change. As electrons are negative in value, the loss of electrons would increase the oxidation state; the gain of electrons, termed as reduction, would decrease the oxidation state. Understand- ably, there cannot be oxidation without reduction and this aspect of chemical reactions is referred to as "redox." One of the most common oxidation reactions involving the element oxygen is found in combustion or fire, which gener- ates heat and light from the rupture of the electron bond. The smoke is the oxidized product of the reaction. Another common one is respiration, the reaction where animals inhale oxygen and exhale carbon dioxide and use the oxygen to oxidize organic nutrients (food), yielding energy. Along with these known reactions are a multitude of other oxidation uses such as hydrogen burning in the presence of chlorine, liberating heat and light just like fire, and producing hydrogen chloride (hydrochloric acid)—which we use in the groundwater industry every day. However, the most notable of the oxidation reactions in groundwater activities are corrosion and disinfection. Defining Corrosion Corrosion is the deterioration of a material due to the inter- action with its environment. Many forms of corrosion that are observed in the groundwater industry are attributed to the electron transfer process and the associated movement of metal ions from one location to another, producing metal deterioration. General or uniform corrosion proceeds uniformly over the entire surface of the metal exposed. The mechanism of attack OXIDATION continues on page 26 Oxygen concentration cell corrosion occurs under some form of deposit that shields a metal surface. A pit is formed in the surface of the metal under the crust of metal oxide. The Oxidation Reaction A friend or foe to the groundwater industry? By Roger Miller Twitter @WaterWellJournl WWJ July 2016 25

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