in summary

The solubility of limescale is based on a chemical balance between carbon dioxide and calcium ions. FrenaCal's catalytic descaling device modifies this balance so that limescale spontaneously crystallizes in the water in a form that does not adhere to it, but floats in the water as nanocrystals.

What is hard water?

Hard water is defined as limescale dissolved in the water. Limescale is insoluble in pure water. If carbon dioxide is added to water, carbonic acid (hydrogen bicarbonate, HCO₃⁻) is formed, and the water dissolves the limescale. The more carbonic acid the water contains, the more limescale it can dissolve, up to a maximum of 16.6 g per liter of water. Limescale is dissolved in water in the form of calcium bicarbonate Ca(HCO₃)₂.

Total water hardness is composed of calcium ions and magnesium ions, with calcium ions accounting for 80% of the hardness. Magnesium behaves chemically similarly to calcium, so calcium is considered representative of total hardness.

How does lime get into drinking water?

Carbon dioxide (CO₂) from the anaerobic decomposition of organic matter in the soil by microorganisms dissolves in rainwater in the form of hydrogen bicarbonate (HCO₃⁻) and forms carbonic acid (H₂CO₃), which filters through the porous limestone rock.

CO₂ H₂O ⇄ H₂CO₃

Dissolved calcium (calcium bicarbonate Ca(HCO₃)₂) is formed by the weathering of limestone (CaCO₃) due to the action of infiltration water rich in carbonic acid.

How is lime dissolved in drinking water and how are lime deposits formed?

Dissolved calcium bicarbonate Ca(HCO₃)₂ is in equilibrium with dissolved carbon dioxide (hydrogen bicarbonate HCO₃⁻). Whether the limescale remains dissolved or crystals form depends on the amount of hydrogen bicarbonate in the water. If the amount of hydrogen bicarbonate is reduced, limescale crystals form. If hydrogen bicarbonate is added, the limescale crystals dissolve.

Hydrogen bicarbonate HCO₃⁻ reacts as a weak base with water to form hydroxide and unstable carbonic acid. A chemical equilibrium is established:

HCO₃⁻ H₂O ⇄ H₂CO₃ OH⁻

To keep calcium bicarbonate Ca(HCO₃)₂ in solution, a certain concentration of what is known as "associated carbonic acid" is required. Chemically, this is no different from any other carbonic acid; what matters is its proportion. This associated carbonic acid maintains, in dissociation equilibrium with the hydrogen bicarbonate ions present, the pH of the water just low enough so that the proportion of carbonate ions, dependent on this pH, together with the concentration of calcium present, does not exceed the solubility product of calcium carbonate.

If there is more free carbonic acid than the "associated" amount in the solution, this additional amount is called "surplus carbonic acid." It can react with more limestone and dissolve it. The proportion of this carbonic acid that dissolves more lime and is converted into additional calcium bicarbonate is called "lime-aggressive carbonic acid." The remaining excess carbonic acid increases the amount of associated carbonic acid to a new, higher level.

CaCO₃ CO₂ H₂O ⇄ Ca²⁺ (aq) 2 HCO₃⁻

Therefore, calcium bicarbonate only exists in aqueous solution in the presence of equivalent amounts of calcium and hydrogen bicarbonate ions.

When do limescale deposits form?

Limescale deposits form when carbon dioxide escapes from water. This occurs when:

· the water evaporates.

· the water heats up.

· water pressure decreases.

As a result, the dissociation equilibrium of carbonic acid shifts back towards the carbonate ions, i.e. to the left in the reaction equation:

CaCO₃ CO₂ H₂O ⇄ Ca²⁺ (aq) 2 HCO₃⁻

This causes the solubility product of calcium carbonate to be exceeded, forming insoluble limescale, for example, on shower walls, water pipes, boilers, and shower heads. This effect can be observed in the home:

· Water evaporates on the shower walls, forming limescale stains.

· The water is heated in the heater, which causes limescale build-up.

· Water comes out through the shower head, where the pressure decreases, causing calcification.

Why are some limescale stains in the shower or sink so difficult to remove?

The limescale deposits that form in contact with soap are not chemically calcium carbonate (CaCO₃), but calcium soaps. These calcium soaps form when hard water reacts with soap and are calcium salts of the fatty acids present in the soap, such as calcium oleate (C₃₆H₆₆CaO₄), the calcium salt of oleic acid, or calcium stearate (C₃₆H₇₀CaO₄), the calcium salt of stearic acid. They are insoluble in water and only dissolve with strong acids, so cleaning them is difficult and normal descaling agents are barely effective.

Should we completely eliminate limescale from drinking water?

It's not a good idea to completely eliminate limescale from drinking water. Calcium and magnesium are essential minerals for the human body; furthermore, limescale-free water is harsh on pipes and can cause corrosion.

Water treatment plants supply "standardized water" by adjusting the carbonic acid content to the level of lime in drinking water so that the carbonic acid dissociation equilibrium shifts slightly towards carbonate ions, i.e. to the left in the reaction equation:

CaCO₃ CO₂ H₂O ⇄ Ca²⁺ (aq) 2 HCO₃⁻

This allows a thin layer of limescale to form on the pipes, which prevents corrosion. To prevent excessive reduction in the pipe's internal diameter, the carbon dioxide content must be constantly adjusted.

How does frenaCal limescale protection prevent deposits from forming?

Limescale protection is based on the principle that when pressure decreases, carbon dioxide is released and small aragonite crystals form, floating in the water.

In the limescale protection system, water flows through a spiral catalyst and swirls. Low-pressure zones are created in the swirling water. In these zones, carbon dioxide is released, and limescale nanocrystals form in the water.

Limescale can crystallize in different forms with distinct properties: calcite and aragonite. When crystallization is slow (in the water heater, shower head, or shower walls), calcite forms, which adheres firmly. However, when crystallization is rapid within the limescale protection system, aragonite forms.

Aragonite produces small crystalline needles that do not adhere, but float in the water and are eliminated with drainage.

How does FrenaCal limescale protection remove existing deposits?

The previously "associated" carbon dioxide released in the catalytic device is converted into "excess" carbon dioxide, changing the chemical equilibrium. This dissolves existing deposits:

CaCO₃ CO₂ H₂O ⇄ Ca²⁺ (aq) 2 HCO₃⁻