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Updated: 08.11.2022 16:01:42

Lime is a universal substance that has found wide application not only in construction, but also in a number of other areas. All thanks to its unique structure and excellent properties (environmental safety among them). It is an excellent «tool» for processing plants, the basis for many building materials, and even a good food supplement. There are 2 main varieties of the substance: slaked and quicklime. How do they differ and can one of them be called more universal? Our experts know about it.

About slaked lime


slaked lime

A practical, simple product of the construction industry, which is deservedly in demand among both professionals and ordinary people. Let us consider in detail the features and properties of this substance.

Production method

Slaked lime is called calcium hydroxide and is formed when water enters it. In the process of transformation of the substance, a large amount of steam is released. After slaking the primary product, milk of lime, water or slaked lime in dry equivalent is obtained. The process of «extraction» of calcium hydroxide or its dehydration is usually carried out in an open space of a large area or in a special creation (box, pit, etc.).

Depending on the rate of quenching, 3 types of calcium hydroxide are distinguished:

  1. Fast-extinguishing (~8 minutes);

  2. Medium extinguishing (~25 minutes);

  3. Slow extinguishing (more than 25 minutes).

The duration of quenching is determined from the moment the lime is combined with water until the reaction temperature stops rising (usually this time period is indicated on the packages with raw materials).

Using lime and water, you can get a lime paste and a hydrate-type substance (fluff). In the first case, water with lime powder is taken in a ratio of 3: 1. To obtain a plastic composition, it is necessary to withstand it for a couple of weeks in a special pit. Fluff is obtained exclusively in industrial conditions: for its manufacture, factories use special hydrotors.

The process of «extraction» of slaked lime is accompanied by the release of a large amount of heat, therefore, in order to avoid a decrease in temperature, water is added gradually. The density of calcium hydroxide can be adjusted by kneading while gradually adding water. As soon as the initial product stops absorbing water, you must immediately stop adding it.


ON A NOTE. Quicklime can have different initial properties, so it is better to choose a longer amount of time for the slaking process. This will help to avoid the appearance of steam on the walls plastered with lime mortar when moisture gets on their surface. A slow-extinguishing composition must be poured with water several times, a fast- / medium-extinguishing composition must be poured until the release of steam stops.

Application and storage

Slaked lime is a very popular product used as an effective fertilizer, whitewash, water softener, and even for dental purposes. Undoubtedly, the main scope of calcium hydroxide is construction. Lime dough is an invariable «participant» in many building mixtures, which is primarily due to its useful properties: immunity to fungus and mold, the ability to «resist» rodents and insects.


ON A NOTE. Immediately after receiving slaked lime, it must be filtered through a special sieve to make the composition more homogeneous, and then gypsum / cement is added to it (otherwise the lime mortar will harden for a very long time).

If slaked lime is obtained in large quantities for the purpose of repeated use, it should be properly stored in order to avoid deterioration of the composition. To do this, unused lime dough is placed in a specially prepared pit and covered with a 20-centimeter layer of fine sand. If we are talking about the cold season, you need to additionally lay out an earthen layer with a thickness of at least 0.7 m in order to avoid freezing of the composition. The storage place is fenced off with marks, which are removed only after the completion of the quenching of the smallest particles of lime.

If it is planned to use slaked lime in building mixtures for masonry, it is enough to withstand the composition for 14 days, if the component is added to plastering mixtures, it should be kept for at least a month.

How to extinguish lime yourself?

When determining the amount of primary raw materials required to obtain a particular amount of lime at the output, it is imperative to take into account the quality of the original product. A simple rule applies here: the higher the quality of the primary product, the more it will turn out in the quenching process.

When slaking lime, it is important to follow a few simple rules (neglecting them will lead to the fact that iron oxide will remain in the finished composition):

  1. The duration of the extinguishing process must be at least 36 hours;

  2. Before starting work, a suitable container is prepared for obtaining lime dough (you can use a metal container — the main thing is that there are no signs of corrosion on its surface);

  3. When adding water to lime, strict proportions must be observed — 1 liter of water is enough to get fluff, for lime dough, the ratio of water and powder should be 1: 2;

  4. After adding water, the components are thoroughly mixed until the release of steam stops;

  5. When extinguishing lime, it is necessary to provide protection for the eyes and hands (use protective gloves and goggles) — this will prevent the possibility of getting burned from a large amount of warm steam released.


ON A NOTE. When creating a slaked mixture for the purpose of spraying plants / trees, the process occurs in a slightly different way. Firstly, the composition is prepared a couple of hours before use. Secondly, the amount of water used must be significant. Thirdly, copper sulfate is added to the main component.

Quicklime: features, obtaining


quicklime

First you need to figure out what quicklime is. This is a substance called calcium oxide. It has a crystalline structure and is obtained by an industrial method. Previously, it was the heat treatment of limestone (calcium carbonate) using mineral additives, quartz sand or slag. But this method is outdated, since the process releases a large amount of carbon dioxide, which is related to asphyxiating gases.

Now in industry, the extraction of quicklime is carried out by the decomposition of calcium salts under the influence of temperature. For such work, shaft furnaces are most often used. The coal-fired varieties make the process of producing calcium oxide very economical, only the furnaces are heavily clogged with ash. Remote furnaces that run on peat, wood and also coal allow you to get better quicklime, but at the same time they are low-power.

In modern construction, or rather, in the composition of the cement mortar, quicklime has already ceased to be used, which is due to its poor moisture resistance: during long-term operation, structures treated with compounds with the addition of quicklime begin to actively absorb moisture — fungus and mold form.

To date, the substance in question in its quick form is used as the main component for a variety of building materials such as slag concrete, coloring agents, plaster, etc. There are also many other ways to use it:

  1. As a primary raw material in the manufacture of silicate bricks;

  2. As a refractory material;

  3. To remove sulfur dioxide from flue gases;

  4. As a dietary supplement;

  5. As a «fuel» for dishes that heat drinks.

Comparative characteristics


Comparative characteristics

In general, the varieties of the calcium product under consideration have a lot in common, but, nevertheless, there are a number of key differences. Our experts conducted a detailed comparison and here are the results.









 


Slaked lime




Quicklime


Chemical formula

Ca(OH)2 (calcium hydroxide)

CaO (calcium oxide)


Structure

White powder that does not emit heat in contact with skin

Granular substance that generates heat on contact with the skin


Interaction with water

Weak

Converts to slaked with the simultaneous release of a large amount of warm steam


Strength level

Average

High


The amount of waste during work

Present

Virtually absent


Scope of application

Construction (main)

Wide


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