Potential of Hydrogen and the Cleanup of Contaminated Aquifers
| Acid is a substance having a sour or sharp flavor. Most foods are somewhat acidic. Foods generally referred to as "acids" include citrus juice, vinegar, and wine. |
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An alkaline substance is comprised of salts and other dissolved materials and is often found in desert soils and water. Most soaps are alkaline.
Alkalis are various soluble salts, principally of sodium, potassium, magnesium, and calcium; substances such as lye, soda or lime. Alkalis neutralize acids.
Acidity and alkalinity have ranges. Substances
that are strongly acidic or alkaline can be corrosive. |
In chemistry we gradate acids and alkalis on a “pH” scale. The pH is a measure of the acidity or basicity (alkalinity) of a material when dissolved in water. It is expressed on a scale from 0 to 14. Roughly, pH can be divided into the following ranges:
pH 0 - 2 Strongly acidic
pH 3 - 5 Weakly acidic
pH 6 - 8 Neutral
pH 9 - 11 Weakly basic
pH 12 - 14 Strongly basic
Materials with pH values of 0-2 or 11.5-14 may be classified corrosive.
The acidity or alkalinity of a solution depends on the number of hydrogen ions (H+) in the solution. The term “pH” means “potential of Hydrogen.” It is a measure of the activity of hydrogen ions (H+) in a solution. |
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In-Situ Chemical Oxidation (ISCO) is a method of destruction of petroleum compounds in soil and groundwater through the process of oxidation. ISCO is used to clean up petroleum contaminated soil and groundwater.
| Oxidation is the act of combining with oxygen. Oxidized metal is rusted. Iron oxide forms red-colored crust. |
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In organic chemistry, oxidation typically results in the breaking up of complex compounds.
Substances that are built of bonds between hydrogen and carbon are called hydrocarbons. Petroleum products create one such family, the petroleum hydrocarbons. Benzene is a petroleum hydrocarbon. It is a carcinogen. When we clean up petroleum contaminated groundwater, benzene is a primary target compound.
The benzene molecule is made of a ring of 6 carbon atoms (in black) clasping “hands” to create the central “ring,” and extending one hand each clasp a hydrogen atom (in white).
The chemical formula is C6H6 where “C” stands for carbon and “H” for hydrogen. |
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| Through oxidation, the benzene breaks up: |
Oxygen + Benzene —> Carbon Dioxide + Water |
In a similar fashion, oxygen breaks up all petroleum hydrocarbons to carbon dioxide and water.
Various methods are used in ISCO: one is the application of hydrogen peroxide. The hydrogen peroxide molecule has two oxygen atoms, and is quite unstable in that it strives to get rid of one and turn into plain water.
In certain applications of hydrogen peroxide in the ISCO process, it has been found that acidic environment is needed for the reactions to take place efficiently. A pH of 3 to 5 was found most productive. This is effected through the injection of sulfuric, citric, or other acids into the treated zone. |
