What is Demineralisation?

Lucy Bell-Young

by Lucy Bell-Young

23rd August 2018

Demineralisation is one of three purification methods used in the water treatment industry. It involves an ion exchange process that yields high-quality, mineral-free water – but this form of water purification isn’t infallible, and it can be trumped.

About Demineralisation

In general, demineralisation is a term used to refer to an absence or reduction of minerals in a given substance. Demineralisation is not exclusive to the water purification industry. In fact, it is a term that is used in a range of industries to refer to different things.

In pathology, for example, demineralisation refers to a deficiency of mineral salts in an organism, but specifically an abnormal loss of mineral salts from the bone. This can lead to things like osteoporosis or tooth decay. In the silk sector, demineralisation is used to remove the mineral layer present in wild Silkworm moth cocoons. This enables them to be wet-reeled into silk.

In the water treatment industry, demineralisation is used in the removal of minerals from raw water in order to yield a high-quality end product that can be used in:

  • Laboratory Testing
  • Analytical Chemistry
  • Cleaning of Lab Equipment
  • Coolant Systems
  • Lead Batteries
Crumpled silk, which demineralisation has a part in manufacturing.

Demineralisation is not only used in water purification. It is also used to demineralise Silkworm moth cocoons so that they can be reeled into silk.

How Does Demineralisation Work?

Demineralised water undergoes deionisation, the same purification method as deionised water. In fact, demineralised water and deionised water are virtually identical and the terms are often used interchangeably.

As with the deionisation process, demineralisation involves passing raw water through an ion exchange resin bed. This is a process in which the impurity ions present water, which are a mixture of positively charged and negatively charged ions, are removed by the ions that get released in the resin bed.

Ion Exchange

There are two types of ion exchange resins used in the resin bed. Cations are positively charged ions with a negative functional group. This allows them to attract any impurity cations present in the water, like calcium (Ca2+), magnesium (Mg2+), sodium (Na+) or potassium (K+), and replace them with hydrogen (H+) ions.

Anions are negatively charged ions with a positive functional group. They attract impurity anions in the water, like chloride (Cl-), bicarbonate (HCO3), nitrate (NO3-) or carbonate (CO32-), and replace them with hydroxyl (OH-) ions. When all the impurity ions have been removed from the solution, the H+ and OH- ions combine to form exceptionally high-quality water (H2O).

Is There a Difference Between Demineralisation and Deionisation?

Since demineralised water is obtained using the principles of deionisation, i.e. ion exchange, it is safe to assume that demineralisation and deionisation do in fact refer to the same process. The only discrepancies between the two methods lies in the subtle differences in the products they yield.

While demineralisation is used to produce mineral-free water, deionisation is employed to yield water that has also had any trace of ionic contaminants removed. In this way, deionised water is higher quality than demineralised water.

For this reason, deionisation may include some additional steps to ensure the exceptional purity of its end-product, such as two-bed deionisation or electro-deionisation (EDI).

A mixing tank in the ReAgent factory

What is the Best Water Purification Method?

There are three main purification methods involved in obtaining different grades of high-quality water. We’ve spoken about two of them already, so what about the third?

Distillation is a process that produces water of even higher purity than demineralisation or deionisation. This is because, unlike the previous methods, distillation does not rely on a chemical reaction. Instead, it is a process of separation in which contaminants are separated entirely from the solution.

In distillation, raw water is boiled until it begins to vaporise. Any impurities present in the water do not vaporise because contaminants have higher boiling points than water. This means that they are left behind while the water vaporises. The vapour is then condensed and converted into distilled water. For even purer results, this product can then undergo double-distillation.

The reason this method yields a purer water sample is because it removes more impurities. Since the deionisation process relies on ion exchange reactions to remove impurity cations and anions, it is not effective at removing organic contaminants, like bacteria, as these do not have a charge.

Therefore, organic impurities are unaffected by deionisation. This is why distillation is the most effective purification method. It is not, however, the most efficient as distillation can be quite costly. This is why, unless distilled water is strictly required, many industries opt for demineralised or deionised water because they are more cost-effective.

Condensation on a surface.

Distillation involves raw water getting boiled until it vaporises. It can then be condensed into high-purity water.

ReAgent has recently welcomed its new-and-improved water treatment plant. This means that we can continue to serve your purified water needs with the highest-quality demineralised, deionised and distilled water products. But if you’re looking for something even better than that, check out our ultrapure water – it’s even more pure than distilled!


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