Chelating Agent / Chelant
A chelant (or chelating agent) is a substance that binds to metal ions —the calcium and magnesium in hard water, or iron— and keeps them «trapped» in solution so that they do not react. In cleaning it prevents limescale from precipitating and water hardness from reducing the detergent's effectiveness. Common examples: EDTA, citrate and polyphosphates.
The word comes from the Greek chele (claw): the molecule binds to the metal ion at several points at once and forms a stable, soluble complex. In practice the term sequestrants is also used, which includes compounds that keep ions in solution even if they do not form a chelate in the strict sense. Besides EDTA, citrate and polyphosphates, detergents use phosphonates, gluconates and other aminocarboxylic acids such as MGDA or GLDA.
In cleaning they perform several functions: they prevent calcium and magnesium from reacting with surfactants, stop limescale from precipitating on tableware, laundry and machines, and hold the iron that can yellow fabrics. How much they are needed depends on water hardness, so it is advisable to know it before choosing a product and dose (see water hardness). A chelant does not by itself remove scale that has already formed; acid descalers are used for that.
Instaquim products containing sequestrants, according to their technical data sheets:
- S Fe (pH 1 %: 10.5; 2–4 g/kg as an additive): wash water additive that forms complexes with iron ions, for ferruginous water; contains EDTA and its salts 5–15 %.
- Duron (pH 1 %: 11.5; 10–12 g/kg of dry laundry): detergent with surfactants and sequestrants for bed and table linen in water of up to 60 ºHF; contains phosphates 15–30 %.
- Deterdur (pH 1 %: 12.5; 1–5 g/l at 55–60 °C): dishwasher detergent with alkalis and sequestrants for water of up to 40 ºHF, preventing scale on tableware and machine; contains phosphonates; not suitable for aluminium.