Calcium oxide

Lime is a term that designates all the physical forms in which calcium oxide (CaO) can appear. It is obtained as a result of the calcination of limestone rocks or dolomites.

Lime has been used since ancient times as a conglomerate in construction, also to paint walls and facades of buildings built with adobes or rammed earth —typical in ancient Mediterranean homes— or in the manufacture of Greek fire.

Definition

Also called: air lime, building lime, chemical lime, masonry lime, flux lime.

Lime (from the Latin calx) is an alkaline substance made up of calcium oxide (CaO), white or grayish white in color, which hydrates or extinguishes when it comes into contact with water, with detachment of heat, and mixed with sand forms a mortar or lime mortar. Alchemists also called lime any metallic oxide or slag.

Another compound called lime is calcium magnesium oxide or calcined dolomite (CaMgO₂).

Aerial lime

Aerial lime is the main binding material in traditional mortars, both for joining and lining. Under the term air lime we refer to a binder of portlandite, calcium hydroxide (Ca(OH)₂), also called slaked or hydrated lime, which over time ends up transforming into calcite, carbonate of calcium (CaCO₃), by carbonation. The carbonation of the hydrates in contact with carbon dioxide from the air, hence its name, forms calcium carbonate that develops some resistance and contributes to the durability of mortars that contain construction lime. Lime has historically been obtained from natural limestone rocks, which are very abundant on the surface of the Earth's continental crust.

Aerial lime is that which requires the presence of air to carbonate and harden. It is a lime that combines and hardens with the carbon dioxide present in the air. When kneaded and mixed with water, it forms a paste that improves the workability –flow and penetration characteristics– and the water retention of mortars. It is technically called CL, for calcium lime, or DL, for dolomitic lime, according to the UNE-EN 459-1 specification.

Calcium limes CL

It is a subfamily of air limes made up mainly of calcium oxide and/or calcium hydroxide without any hydraulic or pozzolanic addition.

DL dolomitic limes

It is a subfamily of air limes made up mainly of calcium and magnesium oxide and/or calcium and magnesium hydroxide without any hydraulic or pozzolanic addition.

Hydraulic lime

Hydraulic lime is that which can set and harden with or without the presence of air, even under water. It is produced by calcining limestone whose composition includes around 20% clay, and which, pulverized and mixed with water, it sets like cement. Hydraulic lime is a natural cement – its acronym in English is NHL (Natural Hydraulic Lime). Hydraulic lime contains, in addition to calcium carbonate, around 20-25% of aluminates, clays, silicates, etc. Due to these "impurities", only a temperature higher than that of the traditional calcination of wood-fired ovens could turn that stone into lime. With the Industrial Revolution and more powerful kilns, a lime with hydraulic characteristics was achieved (despite being 75-80% aerial).

Lime with hydraulic properties, when properly kneaded and mixed with aggregates and water, forms a mortar that retains its workability for a sufficient time and, after given periods, reaches specific strength and long-term volume stability. term. It has the property of setting and hardening when mixed with water and by reaction with carbon dioxide from the air (carbonation).

NHL Natural Hydraulic Limes

Natural hydraulic lime is a lime with hydraulic properties produced by the calcination of more or less clayey or siliceous limestones (including chalk) with reduction to powder with slaking with or without grinding.

The hydraulic properties are the exclusive result of the special chemical composition of the natural raw material.

FL Formulated Lime

Formulated lime is a lime with hydraulic properties consisting mainly of air lime (CL) and/or natural hydraulic lime (NHL) with added hydraulic and/or pozzolanic material.

HL hydraulic limes

Hydraulic lime is a binder made up of lime and other materials such as cement, blast furnace slag, fly ash, limestone filler and other suitable materials. It has the property of setting and hardening with water. Air contributes to hardening.

Slaked lime

Slaked lime is a white powder or paste, composed mainly of calcium hydroxide, obtained by adding water to quicklime. Adding water to quicklime and calcined dolomite produces hydrated products commonly called lime quenched or calcium hydroxide (Ca(OH)₂) and hydrated dolomite (CaMg(OH)₄) respectively.

Manufacturing process

Quicklime is obtained by calcining limestone, with a high content of calcium carbonate (CaCO₃), at a temperature of about 900 °C according to the following reaction:

CaCO₃ + heat → CaO + CO₂

Industrial calcination takes place in vertical or horizontal rotary kilns.

In a traditional way it can be in a traditional, Roman or Arab oven.

Quicklime applications

Lime is one of the best-known products since ancient times and with the most diverse applications.

Industry

• Siderurgia: It is used as a melting and escorifying.

• Metallurgy: It is used in the floating processes; in copper, lead and zinc casting; in the production of magnesium (two types of manufacturing processes can be used: electrolytic process or thermal reduction process, in the latter is used alive lime); in the production of aluminum; and as a sylice scorifier avoiding the formation of aluminium and silica compounds.

• Chemistry: It is used in the production of soap, in the manufacture of rubber and calcium carbide, in the oil industry, in the paper industry and in cosmetics.

• Food: It is used in the sugar industry (especially in the production of beet sugar); in ostriculture; in fish farming; in the brewing industry, in the dairy industry; in the manufacture of queues and gelats, in the treatment of wheat and corn; in the wine industry and in the conservation of food in food containers “autocalentables”, in the nixtamalization of corn.

• Vidrio: Its use provides brighter and more coloured glass. The merger is faster, which means economic savings during the glass manufacturing process.

• Curriculum: It is one of its oldest applications. The lime tiled baths allow hair extraction and swelling of the skins before the tan.

Construction

• Infrastructure: In soil stabilization: to dry wet soils, improve the properties of clay soils.

• Building: In the manufacture of prefabricated lime: Cellular or aired concrete, silicocalcareous bricks and compressed earth blocks. It also emphasizes its historical use for the outer coating of walls ("encalado") in warm areas, giving rise to what are called white villages.

Lime is one more construction product, with its CE Marking and its corresponding standardization (UNE EN-459:1, 2 and 3).

Protection of the environment

• Consumption water treatment (poltabilization): It is used to soften, purify, remove turbidity, neutralize acidity and remove silica (in part sand) and other impurities in order to improve the quality of the water consumed by people.

• Wastewater and mud treatment: It is used in conventional industrial wastewater treatments, basically, inorganic. It is also widely used in the treatment or line of sludge in urban wastewater treatment plants or in organic industrial waters.

• Remineralization of desalinized water: The addition of lime allows to make a conditioning of the desalination water that can go from a pH adjustment and reduction of aggressiveness, to the remineralization of the waters by the contribution of calcium. The lime is essential for the final treatment of the waters from the desalination of the water of the sea since it provides one of the basic nutritional compounds - calcium - and is necessary for the maintenance of the cal-carbonic balance, in order to avoid incrustations or corrosions.

• Gas purification: The lime, depending on the process, is the most profitable and natural desulfurante that eliminates sulfurous anhydride and other acid gases (HCl, HF and NOx) from industrial smokes of urban solid waste incinerators, thermal plants and industry in general.

Lime is also used to remove persistent organic compounds (POPs) such as dioxins and furans, and heavy metals from municipal and industrial incinerators.

• Waste treatment: The lime is used, in addition to being an integral part of various chemical treatments, as an agent for preventing odors and contamination of the water by leaching.

• Treatment of contaminated soils: The techniques used in the treatment of contaminated soils are grouped as follows:

1. Physicochemicals
2. Stabilization - solidification
3. Biological
4. Thermal

In the physical-chemical treatment or method (which constitutes a waste transformation process by adding a series of chemical compounds to achieve the desired objective), lime is used in neutralization, precipitation and dechlorination techniques. Regarding the stabilization / solidification technique (whose main objective is to reduce the mobility and solubility of contaminants present in the soil, reducing their toxicity and eliminating their leaching), there is a variant called "Solidification with lime and pozzolanic materials".

Agriculture

The uses in agriculture are:

• Amendment: The lime is used as an amendment to improve the characteristics of agricultural soils: acidity, porosity and soil biological activity.

• Fertilizer: Provides calcium that is a nutrient for plants.

• Compost (Abono): It is used in obtaining compost from agricultural, agro-industrial and urban wastes.

• Biocidal: It can be used as a biocid whose purpose is to destroy, counteract, neutralize, prevent action or exercise control over any harmful organism by chemical or biological means.

• Animal food: The lime is used as reactive, due to its high reaction speed, for the development of calcium soaps for the manufacture of additives and animal feed derivatives.

In addition, lime is used in acid soils (raising its pH and providing calcium as a nutrient), modifying the composition of the meadows, allowing the development of leguminous species that present better digestibility for cattle and higher protein content. This operation in acid soils will allow a series of species to appear in its floristic composition, including alfalfa, recognized by most farmers as the queen of forage crops.

It is a basic product of natural origin that has two enormous advantages:

• His availability

• His versatilityconsidering the many applications it has, being, in some of them, essential.

Health and safety aspects

• It is classified as an irritant for the skin and for the airways, and implies a risk of severe eye damage.

• Living lime is not fuel, but it generates heat to contact with water, which implies a risk of fire if it comes into contact with low point of inflammation. Therefore, the appropriate extinction measure is to use a dust extinguisher, carbonic foam or carbon gas to extinguish the surrounding fire, never water.

• Living lime reacts exotérmicamente with water to form hydrated lime. When absorbing ambient humidity this reaction is slower and the heat produced can be dissipated without raising the temperature.

Traditions and curiosities around lime

Use as a weapon

The historian and philosopher David Hume, in his history of England, recounts how during the early reign of Henry III the English navy destroyed the invading French fleet by blinding the fleet with quicklime.

D’Albiney used a stratagem against them, which is said to have contributed to the victory: being with the wind in favor, he attacked them with violence; and he threw a lot of lime on the face, which he carried on board for that purpose, blinded them so that they were unable to defend themselves.

It is believed that quicklime was also one of the components of Greek fire. Upon contact with the water, the lime raised its temperature above 150 °C and thus ignited the fuel.

San Martín de Hidalgo (Mexico) and its coat of arms

The coat of arms of the town of San Martín de Hidalgo shows a lime kiln, as a symbol of what has been its main economic activity throughout its history. This municipality was originally called San Martín de la Cal, being founded on February 19, 1540.

Pharaoh Akhenaten

There is an anecdote, which is related to Pharaoh Akhenaten, Nefertiti's husband, who to weaken the economic power and accumulation of land, which was reaching the priestly caste, decreed monotheism, even moving the capital of the country to Amarna. However, at his death, which occurred around the year 1338 a. C., the priests of Amun razed the city covering it with quicklime and decreed the return of the capital to Thebes.

Lime on Roman roads

One of the main applications that the Romans made of lime was in the construction of their roads. A section of the Via Appia would be made up of three strata: The first stratum (statumen) was made of hard, flat stone, cut into large fragments, which in some cases were joined with lime and sand; the second (rudus or ruderatio) was made of broken stone fragments or edges that were agglomerated with greasy lime to give it greater strength and the third (summum dorsum or summa cresta) was made up of large polygonal pieces that fit perfectly together.

The “Calcis Coctores” (lime cookers, lime kilns) of Rome

In the Theodosian Code, an entire chapter (De calcis coctoribus urbis Romae et Constantinopolitanae) is dedicated to the set of rules intended to regulate the work of lime producers, who in turn were the limers of public buildings. This work is a compilation of laws in force during the Roman Empire. Said Code was issued by Emperor Theodosius II in the year 438 AD. c.

Lime in Pliny's Natural History

Gaius Pliny the Second, Pliny the Elder, was born in the year 23 or 24 AD. C. in the North of Italy. His main work is the Natural History , made up of 37 books, which amounts to an encyclopedic compendium of Natural Sciences and where the knowledge exposed in more than 2000 books of Antiquity is collected, many of them lost today In this work, which was frequently cited by scholars of later centuries, there are several references to lime.