Carbon Dioxide

There are many chemicals available on the market today that are suitable for use as neutralization chemicals. The most commonly used chemicals are discussed in an article available here:  Neutralization Chemicals.

Carbon Dioxide - CO₂

Carbon Dioxide (CO₂): The third most concentrated gas found in earth’s atmosphere (preceded by nitrogen and oxygen) CO₂ is it self not an acid. CO₂ forms carbonic acid (H₂CO₃) when dissolved in water; and it is carbonic acid that leads to the neutralization of alkalinity in solution. Carbon dioxide is not easy to use and its use is limited. However, for some applications CO₂ can be a very effective choice. The most appealing feature of CO₂ is that it will not lower the pH of water below 7.0 (for practical purposes). Additionally CO₂ is not corrosive as a gas, however, since CO₂ is heavier than air asphyxiation is always a hazard. Carbon dioxide can be difficult to use because the gas must be dissolved into solution to be used. This requires the use of a carbonator, or some method to dissolve the gas into solution. Generally a tall tank must be used to ensure that there is sufficient fluid pressure to promote the dissolution of CO₂ in water. Significant out-gassing will occur, which is not a problem unless the process also requires the settling of solids.

 

CO₂ + H₂O ↔  H₂CO₃

H₂CO₃ + 2NaOH ↔  Na₂CO₃ +2H₂O

The architecture of a system that uses a gas neutralizing chemical is much different than that which uses a liquid chemical. Therefore the use of CO₂ should be limited to unidirectional systems only (i.e. neutralizing alkaline materials only). Bi-directional systems using CO₂ require the use of a liquid chemical for the alkaline chemical and a gas for the acidic chemical. 

 

Because of our unique design our pH adjustment systems can all be configured to use either liquid mineral acids (such as sulfuric acid) or carbon dioxide. The efficacy of CO₂ as a neutralizing agent should be confirmed in a laboratory, or through pilot testing, before use.

The efficacy of CO₂ decreases with elevated temperatures due to decreasing solubility of CO₂ in solution as the temperature rises. In most cases with a temperature above about 60⁰C the use of CO₂ may be ill advised and mineral acid may be a better choice.

Our hydroTREAT family of pH adjustment systems are specifically designed to use CO₂ to neutralize alkaline influent wastewater particularly wastewater from concrete runoff, hydro-demolition, and mining applications.

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