Sequestering Agent

Definition - What does Sequestering Agent mean?

In chemistry, a sequestering agent is a substance that removes ions from a solution system by forming a ring which does not have chemical reactions with the ion which is removed.

Sequestering agents are commonly used for removing water hardness. They combine with calcium and magnesium ions as well as other heavy metal ions in hard water. They form molecules in which the ions are held so securely (sequestered) that they can no longer react.

Sequestering agents are also known as chelating agents. Chelation is used in treatment of metal poisoning and in industrial extraction of metals.

A sequestering agent is also known as a chelating agent.

Corrosionpedia explains Sequestering Agent

A chemical sequestering agent surrounds another molecule or atom and holds it "in seclusion." In this process, the chemical sequestering agent hides the molecule or atom and prevents it from entering into chemical reactions.

The main types of commercial sequestering agents are:

  • Aminocarboxylic acid base products
  • Phosphates and phosphonates
  • Hydroxy carboxylates
  • Polyacrylates
  • Sugar acrylates

In aqueous solutions, these compounds combine with metal ions, like calcium, to substantially inactivate the ion. Calcium, and other hard water ions, readily combine with surfactants in detergents and reduce their cleaning effectiveness. By inactivating the ion with a sequestering agent, detergents are better able to clean clothes.

Metal sequestering agents can be either liquid or granular. They are used to treat discoloration of pool water, stains or the formation of scale.

As a sequestering agent, polyphosphate is used to sequester soluble iron atoms that remain in settled water before it is chlorinated or that leach off of iron piping in water distribution systems. By surrounding and sequestering these soluble iron atoms, they are prevented from displaying the typical reddish colors associated with iron oxides and iron hydroxides. Scaling can be controlled effectively by the use of sequestering agents and chelates, which are capable of forming soluble complexes with metal ions. Sequestering is not the same as precipitation, because sequestering does not form a solid.

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