Helium in water: why there are no common helium salts

Helium is a noble gas. Under normal natural-water and water-treatment conditions, it does not form common dissolved salts. Its presence in water is therefore described as dissolved gas, not as a chloride, nitrate or sulfate salt of helium.

See also helium in water and the helium element page.

What is present in the water?

Dissolved helium consists of neutral He atoms. This differs from a salt such as sodium chloride, which supplies ions to solution. Dissolving the gas does not make an helium salt, and a conductivity measurement cannot be used as a direct measure of its concentration.

The amount dissolved depends on gas partial pressure, temperature and salinity, as well as whether the water has equilibrated with its surroundings. A solubility value is meaningful only with its gas-pressure and temperature conditions. Dissolved-gas sampling must also avoid unintended exchange with air.

Why there is no salts table

A table of common helium salts in water would imply compounds that are not relevant to ordinary aqueous chemistry. Specialised research on noble-gas compounds under unusual physical conditions does not establish a family of common salts in drinking water or industrial wastewater.

Implications for water treatment

Do not select a salt-removal process solely because dissolved helium has been detected. A dissolved-gas objective needs a gas-transfer assessment: identify the required concentration, feed pressure and temperature, and the gas composition on the other side of the separation.

Where a reduction is needed, evaluate a suitable degassing process against the actual duty. Ion exchange and precipitation act on ionic or solid-forming species and are not direct removal mechanisms for neutral helium atoms. Filtration of suspended solids does not establish dissolved-gas removal. Re-contact with a gas phase can change the final dissolved concentration.

Information for an assessment

Useful inputs include a properly collected dissolved-gas analysis, water flow, operating temperature and pressure, salinity, other dissolved gases, and the process reason for controlling helium. These define a different design problem from removal of dissolved metal salts.