What is the classification of water hardness?

What is the hardness of water?

Some metal cations in water are combined with some anions. In the process of heating water, due to evaporation and concentration, it is easy to form scale, which adheres to the heating surface and affects heat conduction. The total concentration of these metal ions in the water is called water. hardness. For example, the most common metal ions in natural water are calcium ions (Ca2+) and magnesium ions (Mg2+), which interact with anions in water such as carbonate ions (CO32-), bicarbonate ions (HCO3-), sulfate ions (SO42 -), chloride ions (CL-), and nitrate ions (NO3-), etc. combine together to form calcium and magnesium carbonate, bicarbonate, sulfate, chloride, and nitrate hardness. Metal ions such as iron, manganese, and shale in water also form hardness, but since their content in natural water is very small, they can be ignored. Therefore, the total concentration of Ca2+ and Mg2+ is usually regarded as the hardness of water. The hardness of the water has a great influence on the boiler water, so the water should be softened or demineralized according to the water quality requirements of the boilers with different parameters.

What is the classification of water hardness?

There are two types of water hardness: carbonate hardness and non-carbonate hardness.

  • Carbonate hardness: mainly the hardness formed by bicarbonate of calcium and magnesium [Ca(HCO3)2, Mg(HCO3)2], and a small amount of carbonate hardness. Bicarbonate hardness is decomposed into precipitates and removed from water after heating, so it is also called temporary hardness.
  • Non-carbonate hardness: It is mainly the hardness formed by salts such as calcium and magnesium sulfate, chloride and nitrate. This type of hardness cannot be removed by thermal decomposition, so it is also called permanent hardness, such as CaSO4, MgSO4, CaCL2, MgCL2, Ca(NO3)2, Mg(NO3)2 and other carbonate hardness and non-carbonate hardness. The sum is called total hardness; the content of Ca2+ in water is called calcium hardness; the content of Mg2+ in water is called magnesium hardness; when the total hardness of water is less than total alkalinity, the difference between them is called negative hardness

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Further reading:

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