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Phosphoric Acid

Phosphoric acid is a clear, odourless liquid, which is non-volatile. It is slightly viscous with a syrupy consistency when concentrated.

It is typically available in 85% concentration and in more dilute solutions for various commercial and laboratory uses. 

Depending on the concentration, the S.G. ranges from 1.3-1.95. At 85% concentration, phosphoric acid is corrosive and extremely harmful to skin and eyes. When diluted the acid may become non-toxic and is suitable for consumption.

Applications

  • The majority of phosphoric acid is used in the production of fertilizer where the acid is reacted with the minerals found in phosphate rock to produce phosphate salts.
  • For use in rust treatment, phosphoric acid solutions are created as a dipping bath or gel to applied to rusted areas.
  • Phosphoric acid also used for the etching of metal and the roughing of tooth enamel during dental treatments such as root canals and tooth whitening.
  • For its sharp, tangy taste, phosphoric acid is used as a flavouring in many soft drinks, typically colas. 
  • Other uses include pharmaceuticals, cleaning products and as a chemical reagent.

Pumping considerations

It is strongly recommended using a sealless pump such as a mag drive pump, removing any risk of leakage. The absence of mechanical seals prevents the occurrence of abrasive wear on a seal between the fluid and atmosphere. All mechanical seals require regular inspection, require replacing. By replacing a mechanical seal arrangement with an o-ring assembly the inherent risk of a seal failing is removed. 

It is very important to consider the S.G. as it can vary considerably. For specifying a mag drive pump the impeller will need to be trimmed accordingly to prevent the motor from overworking and decoupling. 

Metals can be specified however some may incur a short working life. Hastelloy, specifically B-3, G-30 and G-35 are excellent for pumping even concentrated phosphoric acid. Some stainless steel grades are usable, however these may suffer a high rate of corrosion and incur a short working life.  As the acid reacts with stainless steel, and vapours can be flammable. A non-metallic lining can be recommended for better chemical resistance.

PTFE, Viton and Kalrez elastomers can be used, though at higher concentrations Buna N and natural rubber should be avoided.

For dosing of phosphoric acid, a peristaltic pump can be used with EPDM hose and non-metallic inserts at the flange ports.