pH control after cleaning with Caustic

[rosshol]

Hi,

We currently clean our equipment with Caustic in large quantities. In order to control our effluent pH we neutralise at source using phosphoric acid as it is cheap. However, our safety guy is not convinced that this is the best option. Is there a better chemical that could be used?

Thanks in advance.

ROSS

 

[sshep]

Phosphoric acid has the added benifit of being triprotic and forms a buffer solution so overshoot is less of an issue as with HCL etc. In addition it seems pretty wastewater treatment friendly- i.e. micro-organisms learn to love it.

The main hazard is that it is an acid, and therefore cause a corrosive burn to skin. PPE and safe handling procedures are obviously required. Sorry I can only offer a defensive explanation for phosphoric acid because we generally use acids to nuetralize caustic. Other good alternatives are unknown and untried for me. Does your safety guy have any specific concerns or alternatives to offer?

best wishes, sshep

 

[epoisses]

What else than an acid can you use to neutralise caustic? If you really want to improve safety, consider a different way of cleaning than with caustic.
What kind of contamination do you need to remove?

 

[bimr]

Phosphoric acid is a safe and inexpensive acid to use for the neutralization of alkaline materials. It is probably your best option from a health and safety standpoint provided that you are not using large volumes of caustic.

Phosphoric is a weak acid. Unlike sulfuric or hydrochloric it will not fully disassociate in water at normal concentrations. This renders phosphoric safer to use than sulfuric or hydrochloric and evolution of gasses is rarely, if ever, a problem.

Due to its weak disassociation constant, phosphoric acid does not react with the normal logarithmic response as a strong acid and tends to buffer neutralization reactions. This makes for a slower pH neutralization reaction that is easier to control.

Phosphoric acid does not compete well with sulfuric and hydrochloric acid for large volume users because it is more expensive. Because of the higher cost (as compared to sulfuric) and availability, phosphoric acid is not commonly used in neutralization systems that require large volumes of acid.

http://www.phadjustment.com/NeutralizationChemicals.htm