Hardness and damage of hard water

The pH index relates to the hardness and grip of water. When the hardness and grip are stable, the pH is less changed.


1. Hardness of water

The hardness of water is determined by the content of soluble minerals in water, mainly because the salts contain Ca ++ and Mg ++ ions. The hardness of water is divided into 2 types:

  • Temporary hardness or hardness of carbonate: Created by the salts of Ca and Mg carbonate and bicarbonate, which are mainly bicarbonate because of the salts of carbobate Ca and Mg are almost insoluble in water. Called temporary hardness because we can reduce it by many simple methods. In nature, temporary hardness of water also changes frequently under the influence of many factors, such as temperature ...
  • Permanent hardness: Created by other salts of Ca and Mg such as sulphate, chloride ... can only be changed by complicated and expensive methods.

Usually people are only interested in temporary hardness of water because it has more impact than permanent hardness. There are many different units of hardness measurement, but most people use 3 units of measurement: dH, mg / liter and ppm. For simplicity, when measuring hardness people often refer to a type of salt is CaCO3.

Water with temporary hardness greater than 100 ppm is considered hard water, below that level is considered soft water.

2. The impact of hard water

Permanent hardness of water has little effect on organisms unless it is too high, on the contrary, temporary hardness has a great effect. The main reason is that the main components that create temporary hardness are bicarbonate Ca and Mg: Ca (HCO3) 2 and Mg (HCO3) 2, they are completely soluble but unstable and unstable. They are easily decomposed into CaCO3, MgCO3 are precipitated salts:

Ca (HCO3) 2 => CaCO3 + H2O + CO2
Mg (HCO3) 2 => MgCO3 + H2O + CO2

When decomposition reactions occur in the organism, these salts precipitate in the organism to cause significant harm. In humans, they are the cause of kidney stones and one of the causes of arterial obstruction is due to limestone deposits in the inner walls of the arteries. Note that CaCO3 and MgCO3 salts are precipitated salts and that they do not penetrate our gastrointestinal mucosa, only soluble salts are permeable. So hard water is only harmful by bicarbonate salts.

3. Water softening methods

There are many methods to reduce the hardness of water, from simple to complex.

a. Heat the water
Water heating will significantly reduce water hardness

b. Making water flow constantly
Continuous stirring or continuous circulation pumps are also effective, although quite slowly and in many cases, bicarbonate decomposition is slower than the dissolution of bicarbonate from other sources into the water.

c. Distilled water
In principle, distilled water can be considered completely pure H2O.

d. RO Filter (Reverse Osmosis)
RO filtration technology allows the removal of almost all soluble and insoluble substances from water, RO water can be considered pure H2O (though not by distilled water).

e. Ion exchange
This is the most commonly used method because of its low cost including investment costs and operating costs. Its principle is to pass water through a material containing positive ions that are more active than Ca ++ and Mg ++, which will absorb Ca ++ and Mg ++ ions in the water and release those stronger ions, thus creating Carbonate compounds do not precipitate. That material is called Cationit (or cation-exchange resyn). Normally, two types of cationite are Na-Cationite and H-Cationite corresponding to the ions of Na + and H + and the compounds created respectively Na2CO3 and H2CO3 (H2CO3 will be immediately analyzed into H20 and CO2)

When the Cationite has exhausted its ability to exchange, one must "revert" to restore its positive ions. For Na-Cationite, NaCl salt is used, for H-Cationit, acid is used.

The conventional Na-Cationit exchange device can lower the hardness of water to below 10 ppm, if specially designed it can be lowered below 2 ppm. Each liter of Na-Cationite particles is capable of exchanging between 2-6 grams of equivalent depending on the type, ie it is possible to reduce the hardness from 300 to 1000 liters of water with a hardness of 6 mgdl / liter (300 ppm or 16.8 dH) to 0 before reverting.

H-Cationite has a stronger exchange capacity than Na-Cationite and is also more radical because it completely removes carbonate radicals from the water. However, it has many times higher cost, higher operating cost (acid is more expensive than table salt) and the operation requirement is also more stringent due to the use of acid so it is rarely used.

In addition to exchanging positive ions, it also uses negative ion exchange (an exchange agent called Anionite) to remove HCO3- ions from the water. This method is often used only in thermal power plants, where they use both Na-Cationit, H-Cationit and Anionit in a single system.