Magno (chemical)

With Magno chemical products are referred to that of the mineral dolomite are produced. These products are required for some processes in water treatment.

Manufacturing

When dolomite is carefully heated, only the magnesium-bound carbon dioxide (CO ₂ ) is split off first, depending on the selected temperature range and exposure time . The product after splitting off a molecule of CO ₂ is called Magno. When the second CO ₂ is split off , burnt dolomite is formed . More on the required temperature ranges for CO ₂ degradation under dolomite .

The reaction equations for the formation of the products below:

1st stage

${\displaystyle \mathrm {CaCO_{3}} \cdot \mathrm {MgCO_{3}} \rightleftharpoons \mathrm {CaCO_{3}} \cdot \mathrm {MgO+CO_{2}} }$

Dolomite splits off carbon dioxide with the formation of magno

2nd stage

${\displaystyle \mathrm {CaCO_{3}\cdot MgO\ \rightleftharpoons \ CaO\cdot MgO+CO_{2}} }$

Magno splits off carbon dioxide with the formation of burned dolomite

Magno obtained from the mineral dolomite is called Magno-Dol , whereas synthetically produced magno-Syn is called. While Dol is split-shaped, the granulate form is called Magno-Gran . Similar to burnt lime , burnt dolomite and water form a hydrate, the magnohydrate , with the formation of heat .

The reaction equation for this:

${\displaystyle \mathrm {CaO\cdot MgO\ +\ H_{2}O\ {\xrightarrow {\triangle H<0}}\ Ca(OH)_{2}\cdot MgO} }$

Burnt dolomite reacts with water to form magnohydrate, generating heat

Magnohydrate has a significantly higher basicity than magno when it comes into contact with water due to the proportion of calcium hydrate.

use

Magno - both Dol and Syn - reacts with free carbonic acid in water to form calcium and magnesium hydrogen carbonate. Magno is a relatively weakly basic material in the presence of water. Because of the low basicity, only the aggressive carbonic acid reacts with a shorter exposure time . The low alkalinity is not sufficient for a reaction with all the free carbon dioxide. The equation for this reaction is as follows:

${\displaystyle \mathrm {CaCO_{3}\cdot MgO+3CO_{2}+2H_{2}O\longrightarrow Ca(HCO_{3})_{2}+Mg(HCO_{3})_{2}} }$

Magno binds carbon dioxide in the water with the formation of calcium and magnesium carbonate hardness

The carbonate hardness of the water increases as a result of the reaction by the stoichiometric amount of the set free carbon dioxide. Since only the aggressive carbon dioxide reacts, after treatment with Magno a water without (lime) aggressive carbon dioxide is formed. This as well as various other processes - only removal of the aggressive carbon dioxide - are called deacidification in water technology .

The reaction rate for this acidification is both temperature- and p _H -dependent as well as depending on the content of carbonate in the treated raw water. Waters with lower levels of carbonate hardness and higher temperatures react faster with Magno. The reaction is hindered by the amount of iron and manganese dissolved in the water, especially in the presence of dissolved oxygen. The reason for this is the deposition of oxide hydrates on the surface of the Magno-Material and the resulting disruption of the exchange of substances.

The main applications with Magno are:

• Production of drinking water in smaller local treatment plants. Raw water with aggressive carbonic acid flows through a filter filled with Magno in order to bind the aggressive carbonic acid.
• Neutralization of mineral acid wastewater, as Magno binds free acids faster than unburned lime or dolomite. The wastewater flows through a pit or container filled with Magno. However, only water with a relatively low solids content, which also has a low content of free sulfuric acid (risk of gypsum formation!), Is suitable for this type of neutralization.
• Another application is hot desilification . Due to its high basicity, magnohydrate reacts with the free carbonic acid, the carbonate hardness as well as with the silica in water. More about this under decarbonization .

See also

• Tillmans formula

literature

• Babcock manual water, chapter: Deacidification, Magnofiltration and hot decilification
• bbr 5/97, Martin Sölter