Hydrochloric acid

(endorsed 2005)

Hydrochloric acid is used to correct pH, regenerate deionisers and generate chlorine dioxide on site.

General description

Hydrochloric acid, HCl, also known as spirits of salts, is a colourless or slightly yellow, fuming, pungent liquid. This strong and highly corrosive acid should be handled with extreme caution (particularly when adding the concentrated acid to water), as it can cause severe burns and eye damage. Hydrochloric acid is generally available as a 25–42% solution. A 28% solution has a specific gravity of 1.14 at 20°C. The acid is soluble in water and benzene, and is noncombustible.

Hydrochloric acid is highly corrosive to most metals or alloys, liberating extremely flammable hydrogen gas. Chlorine gas may also be liberated in reactions with oxidants or sodium hypochlorite. Hydrochloric acid may be stored and piped in rubber-lined carbon steel, fibreglass-reinforced plastic with acid-resistant resins, plastic liners and pipes (u-polyvinyl chloride, polythene and polypropylene).

Chemistry

Hydrochloric acid is manufactured by the combustion of chlorine gas in hydrogen to produce hydrogen chloride gas, which is then dissolved in water.

Hydrochloric acid disassociates in water to produce a strong acid:

$$\text{HCl}\leftrightarrow\text{H}^{+}+\text{Cl}^{-}$$

To reduce fuming, the acid should be diluted (by adding acid to water) to about 20% HCl.

Typical use in Australian drinking water treatment

In drinking water treatment, hydrochloric acid is used to correct pH (for softening, corrosion control, coagulation, prevention of post-precipitation), regenerate deionisers and generate the disinfectant chlorine dioxide on site.

Doses of hydrochloric acid required vary widely, depending on the application and conditions.

Contaminants

The purity of chemicals used in Australia for the treatment of drinking water varies, depending on the manufacturing process. The following chemical contaminants may be present in this product (JECFA, KIWA 1994):

• arsenic

• chlorine

• chromium

• iron

• lead

• methylene chloride

• nickel

• sulfate

• sulfur dioxide

Residual and by-product formation in drinking water

When employed in drinking water treatment, hydrochloric acid should be used in such a way that any contaminant or by-product formed by the use of the chemical does not exceed guideline values in the Australian Drinking Water Guidelines.

Status

Hydrochloric acid was endorsed by the NHMRC for use as a drinking water treatment chemical in 2005.

References

Clesceri Wastewater, 20th edition. American Public Health Association, Washington, DC.

JECFA (Food and Agriculture Organization of the United Nations (FAO)/World Health Organization (WHO) Joint Expert Committee on Food Additives). Compendium of Food Additive Specifications. FAO Food and Nutrition Papers 52 (two volumes). Available at https://www.who.int/foodsafety/publications/jecfa/en/

KIWA (1994) Guideline quality of materials and chemicals for drinking water supplies. Inspectorate of Public Health and Environmental Planning, Publication 94-01. Rijswijk, The Netherlands.