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Through the addition of solid calcium carbonate to a water sample followed by constant stirring for a period of time, either part of the salt will dissolve or the water will remain unchanged. By examining the sample prior to and after the addition of calcium carbonate, one can quantitatively determine whether it is lime-aggressive or not.

The malt is placed in a stainless steel wire sieve drum. For a designated time period, the kernels are pressed against the rotating wire sieve drum by a roller, whereby the friable portion of the malt falls through the sieve, while the glassy portion is retained in the drum.

According to DIN 38409 part 6 (January 1986) “hardness” is defined as the calcium and magnesium ion content of a water sample. In particular cases, barium and strontium ions may also contribute to hardness. Even though the term hardness is not a scientific one and in principle is even legally objectionable since no SI unit exists for it, hardness is still indispensable, as it simplifies the terminology. For this reason, the somewhat dated units are still deemed acceptable alongside the current mg/l, mval/l and mmol/l. The unit “Deutscher Grad” (degrees German hardness), 1 °d (in the past, also known as 1°dH) is equivalent (based on CaO) to 0.3566 mval = 0.179 mmol/l: *)

*) SI units recognized in legal and commercial transactions, whereby °d should be expressed in mmol/l

10.00 mg/l CaO = 7.15 mg/l Ca²⁺ = 0.3566 mval/l

7.19 mg/l MgO = 4.34 mg/l Mg²⁺ = 0.3566 mval/l

For the unit 1 mval/l, the values shown above are higher by a factor of 2.804 (1/10 of the CaO equivalent weight).

28.04 mg/l CaO = 20.04 mg/l Ca²⁺ = 2.804 °d

20.15 mg/l MgO = 12.15 mg/l Mg²⁺ = 2.804 °d

An alkaline earth ion concentration of 1 mg/l corresponds to:

1 mg/l Ca²⁺ = 0.1399 °d = 0.0499 mval/l hardness

1 mg/l Mg²⁺ = 0.2306 °d = 0.0822 mval/l hardness

Calcium and magnesium are the principal alkaline earth metal ions found in natural waters.

For certain applications and/or treatment processes, knowing the total hardness is insufficient, since understanding which alkaline earth metals are responsible for it is important (usually calcium or magnesium ions). These cations are also paired with anions, in which case the ions of carbonic acid play a significant role (carbonate and hydrogen carbonate ions).

The subgroups of hardness can be characterized as follows:

Calcium or lime hardness (Ca-H):

The portion of the water hardness caused by calcium ions.

Magnesium or magnesia hardness (Mg-H):

The portion of the water hardness caused by magnesium ions.

Total hardness (TH):

This term encompasses the sum of the individual types of hardness (Ca-H + Mg-H).

Carbonate hardness (CH):

The carbonate hardness corresponds to the concentration of alkaline earth metal ions equivalent to the hydrogen carbonate and carbonate ions present in the water. These ions are measured in mval/l through determination of the m value. Water that does not require acid for neutralization to reach the m value possesses no carbonate hardness (pH < 4.3). The m value corresponds to the carbonate hardness in mval/l. This is true as long as this value does not exceed the total hardness in mval/l, since by definition the carbonate hardness cannot exceed the total hardness. Water with an m value that exceeds the total hardness in mval/l is called “sodium alkaline” since it contains sodium. In selecting the treatment process, it is advisable to differentiate between calcium and magnesium carbonate hardness (Ca-CH and Mg-CH).

Non-carbonate hardness (NCH):

This is defined as the difference between total hardness and the carbonate hardness and thus, as that portion of calcium and magnesium ions for which no equivalent bicarbonate and carbonate ions are present in the water, but for which an equivalent quantity of other ions exist (e.g., hydroxide, chloride, sulfate, nitrate, phosphate, silicate, humate). Waters, whose m value is ≥ TH (mval/l), do not exhibit non-carbonate hardness.

Required analysis data:

• calcium ion content in mg/l or mval/l

• magnesium ion content in mg/l or mval/l

• acid required to reach the m value in mval/l

The residual alkalinity is calculated using the following parameters: total hardness, calcium hardness and magnesium hardness.

Through the addition of lime water or 'milk of lime,' the hydrogen carbonates and free carbon dioxide are transformed into carbonates and are then largely precipitated:

Ca(HCO₃)₂    +  Ca(OH)₂     →  2 CaCO₃  + 2 H₂O
Mg(HCO₃)₂    +  Ca(OH)₂    →     MgCO₃ + CaCO₃ + 2 H₂O
CO₂           + Ca(OH)₂    →  CaCO₃ + H₂O

Calcium carbonate is insoluble and precipitates out. By contrast, magnesium carbonate is to a large extent soluble in water. The addition of one more equivalent weight of Ca(OH)₂ transforms magnesium carbonate into insoluble magnesium hydroxide:

MgCO₃          + Ca(OH)₂    →  CaCO₃ + Mg(OH)₂

However, the amount calculated for this form of water treatment would lead to a surplus of lime in the water (and a higher than desired pH), since an especially high alkalinity is required for the quantitative precipitation of magnesium hydroxide. Therefore, the “split treatment” method, as it is known, is preferred, i.e., the quantity of lime water calculated for the total quantity is added to ⅔ of the untreated water. An excess of lime results, and therefore, the magnesium hydrogen carbonate is also precipitated. The addition of approx. ⅓ of the untreated water diminishes the lime surplus and causes the complete precipitation of calcium hydrogen carbonate. By doing so, the hardness caused by calcium carbonate is entirely eliminated, and the hardness caused by magnesium carbonate is to a large extent as well.

Determination of the quicklime (CaO) or sodium hydroxide (NaOH) content of the detergent solution with an acid solution (HCl or H₂SO₄) with corresponding equivalent concentration (normality) up to the color change of phenolphthalein (pH 8.2).

Quicklime

Sodium hydroxide