SEQUESTRATION

A sequesterant is an agent which prevents an ion from exhibiting its normal properties by complexing with it. Some sequestrants are threshold inhibitors because they function below stoichiometric levels.

Other sequesterants which depend on stoichiometric reactions between themselves and deposit components are called chelants.

A sequestrant which is acting through non-stoichiometric reaction is normally a water soluble polymer, having many active functional groups attached. Those functional groups are mixtures of ionic and non-ionic functionality.

The non-ionic functional groups are mostly amide or hydroxyl groups.

At the early beginning of this technology the ionic functional groups were anionic of carboxylic type or cationic of polyamine. Now the use of cationic groups is prohibited due to environmental restrictions, because they are extreme marine life pollutants.

In most countries around the globe is even its production prohibited. So are still produced (and maybe used), only in countries and plats which are sufficiently bold to not respect environmental international agreements and to risk for the penalties.

The anionic functional groups are mostly carboxylates, but sulfonic or phosphonic functional groups are for a less extent in use, mostly as a mixture with carboxylates at the same polymeric chain.

By its nature these anionic functional groups have very high chemical affinity to calcium ions, higher than the water ions that are participating to the formation of the scales (carbonates, sulfates, silicates).

So the calcium ions are attracted from the functional groups, but they cannot react, due to stereochemical barriers created from the polymeric chain, remains at the surrounding and creates a calcium ions layer. This calcium zone has cationic potential and attracts normal water anions (mostly carbonates and sulfates, chloride and almost other anions but not silicates).

The anions attracted by calcium layer, approach the calcium layer, but cannot reach it and react, because are approaching also the polymeric chain to which the calcium layer is surrounding, and are repulsed from the anionic functional groups of the sequestrant.

This anion layer creates anionic potential and attracts new calcium, which approaches the anion layer, but cannot reach it, repulsed from the calcium of the inner layer, creating a second calcium layer, which attracts a new anion layer.

Finally a polymeric sequestrant it is creating around it a “cloud” of ions, through electrochemical attractions and interactions, confirmed by electronic microscope scan. According to the nature of the sequestrant, its concentration and the water characteristics, this “cloud” can contain 4-10 calcium and equivalent anion layers.

Those ions, being in the water are actually not available to react between them and to create chemical deposits. But will be found in a very accurate and intensive chemical analysis, because there are there. In a spot analysis, like at the normal test kits, the sequestrant can interfere and the indication will be non-very accurate.

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