What is Lime?

Lime chemical terminology explained - click here
Building lime terminology explained - click here
Other chemical & misc. terminology explained - click here

Lime is made from calcium carbonate. This can be found in a variety of forms for example chalk, limestone or sea shells. In the British Isles sources are almost invariably chalk or limestone. In the case of Singleton Birch, it is mainly chalk quarried in Lincolnshire.

To convert the raw material into lime, heating to temperatures between 800 C - 1000 C is required. At these temperatures the chalk breaks down by giving off carbon dioxide leaving calcium oxide which is known as quicklime.

Quicklime is unstable and reacts, often very rapidly, with water to form calcium hydroxide. This process produces heat and is known as hydration. When exposed to the atmosphere this calcium hydroxide can react again by absorbing carbon dioxide from the atmosphere to once again become calcium carbonate.

This is known as the lime cycle and is shown in the diagram below.

It is calcium hydroxide which, when mixed with sand to make a mortar, builders have used over the millennia. The setting process is the re-absorption of carbon dioxide from the atmosphere called carbonation.

Calcium hydroxide can be used by Builders in two forms, firstly, if it is hydrated with an excess of water, lime putty is produced or if the water quantity is reduced a powder is formed which can be bagged.

All sources of pure calcium carbonate produce a similar result, however the Romans discovered that the calcium hydroxide would also react with volcanic ash, essentially a mixture of silica and alumina. The resulting mixes set very much harder and for the first time enabled structures of high strength to be built. By varying the quantity of silica and alumina, mortars (and lime concretes) of different strengths could be produced. These reactions are referred to as pozzolanic, from the town of Pozzuoli in Italy from where the original material came.
The processes described so far use chalk or limestone that is relatively pure containing over 95% calcium carbonate. However some limestones are less pure and can contain quantities of silica and alumina which when heated produce very similar results to the Roman mixes of pure lime with volcanic ash. These impure limestones if they contain quantities of silica and alumina are referred to as Natural Hydraulic Limes (NHL).

Hydraulic in this context refers to the ability of the material to set under water as opposed to pure air limes which can only set when exposed to atmospheric carbon dioxide. As with addition of pozzolanic silica and alumina, the strength of NHL's depends upon the quality of these materials in the limestone. As the quantities increase so does the strength but also the free lime (calcium hydroxide) in the mortar reduces so that the set depends more on chemical reaction and the process of carbonation reduces.

Singleton Birch have worked to develop a range of NHL products by sourcing the appropriate chalk or limestone for burning, based on its' geology and mineralogy.
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Lime terminology
calcium carbonate
also known as: chalk, limestone, agricultural lime
chemical formula: CaCO3

calcium oxide
also known as: quicklime, burnt lime
chemical formula: CaO

calcium hydroxide
also known as: hydrated lime, slaked lime
chemical formula: Ca(OH)2
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Building Lime terminology
Air lime
Air lime, or high calcium lime does not have any hydraulic component. It can be quicklime for slaking or hydrated lime. It gains strength slowly, by combining with atmospheric carbon dioxide to form calcium carbonate (as per the lime cycle). Several grades of air lime are identified in EN459 the European standard for Building Lime.

Hydraulic lime
Lime with hydraulic or cementitious properties which will set when exposed to moisture. Several grades of hydraulic lime are identified in EN459 the European standard for Building Lime.

Natural hydraulic lime
Hydraulic lime which does not contain any performance enhancing additives. Its properties are as a result of the mineralogy of the calcium carbonate stone which is quarried for burning.

Hydrated lime
Hydrated lime is NOT hydraulic lime and will not set in contact with water.

CL90 & CL90 S
Grades of air lime for building as described in EN459 the European standard for Building Lime. CL90 is the purest grade of building quicklime and CL90 S is the purest grade of hydrated lime for building. Several grades of air lime are identified in EN459 the European standard for Building Lime.

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Other chemical & misc. terminology
carbon dioxide
chemical formula: CO2

water
chemical formula: H20

silica
chemical formula: Si02

alumina
chemical formula: Al203


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Lime Mineral Data

Help on Chemical Formula: Chemical Formula: CaO
Help on Composition: Composition: Molecular Weight = 56.08 gm
Calcium 71.47 % Ca 100.00 % CaO
Oxygen 28.53 % O
______ ______
100.00 % 100.00 % = TOTAL OXIDE
Help on Empirical Formula: Empirical Formula: CaO
Help on Environment: Environment: Thermally metamorphosed calcareous ejecta.
Help on IMA Status: IMA Status: Valid Species (Pre-IMA) 1935
Help on Locality: Locality: Vesuvius, Campania, Italy Link to MinDat.org Location Data.
Help on Name Origin: Name Origin: Named from the Old English, quicklime.
Help on Name Pronunciation: Name Pronunciation: Lime Say LIME
Help on Synonym: Synonym: Calcium Oxide
Chaux
ICSD 75785
PDF 37-1497

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Chemical of the Week

LIME: CALCIUM OXIDE -- CaO

Calcium oxide is a white crystalline solid with a melting point of 2572°C. It is manufactured by heating limestone, coral, sea shells, or chalk, which are mainly CaCO3, to drive off carbon dioxide.

500–600°C

CaCO3(s)


--


CaO(s) + CO2(g)

This reaction is reversible; calcium oxide will react with carbon dioxide to form calcium carbonate. The reaction is driven to the right by flushing carbon dioxide from the mixture as it is released.

The production of calcium oxide from limestone is one of the oldest chemical transformations produced by man. Its use predates recorded history. Most ancient languages have a word for calcium oxide. In Latin it is calx, from which the name of the element calcium is taken. In Old English, its name is lïm, which is the origin of the modern commercial name for calcium oxide, namely lime. The abundance of limestone in the Earth's crust and the ease of its transformation to calcium oxide do not alone explain why the lime is one of the oldest products of chemistry. Lime has many properties that make it quite valuable. It is so useful, that it is today produced industrially on a vast scale; over 20 million metric tons were produced in the U.S. in 2000.

The oldest uses of lime exploit its ability to react with carbon dioxide to regenerate calcium carbonate. When lime is mixed with water and sand, the result is mortar, which is used in construction to secure bricks, blocks, and stones together. Mortar is initially a stiff paste that is laid between the bricks. It gradually hardens, cementing the bricks together. At room temperature, the reaction of lime with carbon dioxide is very slow. It is speeded by mixing lime with water. When lime is mixed with water, it forms calcium hydroxide, called slaked lime.

CaO(s) + H2O(l)


--


Ca(OH)2(s)

The reaction of calcium hydroxide with carbon dioxide is faster, producing a mortar that hardens more quickly.

Ca(OH)2(s) + CO2(g)


--


CaCO3(s) + H2O(l)

Even with the increased reaction speed, mortar requires many years for complete reaction to occur. Other lime&endash;based products used in the construction industry include lime plaster and portland cement.

Perhaps the most commercially important property of lime is its ability to form solutions with silicates. When lime is heated with silica sand (SiO2) and sodium carbonate (Na2CO3), a solution is formed that does not crystallize when it is cooled. Instead it hardens to an amorphous, clear, and nearly colorless solid, namely glass. Because it is a mixture and not a pure compound, glass does not have a distinct melting point; it gradually softens as it is heated. Therefore, it can be molded and blown into many useful shapes. The production of glass from lime is another of the ancient uses of lime.

The most important modern use of lime also relies on its ability to form solutions with silicates. Nearly 45% of lime is used in the steel industry. Steel and iron are produced from ores, which are rocks that contain iron oxides. Many of these ores also contain a large amount of silicates. When lime is mixed with the ore and the mixture melted, these silicates combine with the lime, forming a liquid solution called slag. Slag is immiscible with molten iron, so the silicates can be removed from the iron by draining o the slag. Approximately 80 kg of lime is used in the production of each metric ton (1000 kg) of iron. Lime is also used in the production of other metals. For example, it is used to remove silicates from alumina (Al2O3) before the alumina is reduced to aluminum metal.

Lime is also an important material in the manufacture of chemicals. Its major use here is in the production of calcium carbide, CaC2. Calcium carbide is manufactured by heating lime with coke.

2 CaO(s) + 5 C(s)


--


2 CaC2(s) + CO2(g)

Calcium carbide reacts with water, releasing acetylene, C2H2.

CaC2(s) + 2 H2O(l)


--


C2H2(g) + Ca(OH)2(aq)

Acetylene is an important fuel for welding and is also a starting material for a range of organic compounds, including vinyl chloride, neoprene, and acrylonitrile, all of which are raw materials for polymers.

Pollution control is a rapidly expanding consumer of lime. Lime is used in stack gas scrubbers to reduce sulfur dioxide emissions from power plants. Sulfur dioxide reacts with lime to form solid calcium sulfite.

SO2(g) + CaO(s)


--


CaSO3(s)

Lime is also added to sewage to remove phosphates.

3 CaO(s) + 3 H2O(l) + 2 PO43–(aq)


--


Ca3(PO4)2(s) + 6 OH–(aq)

The pretreatment of water supplies involves the use lime to decrease the acidity, to soften, and to clear drinking water.

A variety of other industrial processes also make extensive use of lime. It is used as an opacifier in plastics. The paper industry uses it in pulping wood; because lime is highly alkaline, it dissolves the lignin that binds the fibers together in wood. In the refining of sugar, lime causes coagulation of plant material, allowing it to be more easily separated from the sugar syrup.

Calcium oxide no longer produces the limelight in theaters. The theatrical use of lime has disappeared, leaving only its name, suggesting the romance of a bygone era. Because lime has a very high melting point, it can be heated to a very high temperature without melting. Substances with such high melting points can be heated to white heat, a temperature so high that the light they emit is white. Before the advent of electric lighting, white stage lighting was produced by heating lime in the flame of a torch, and this light was called limelight.

CALCINED DOLOMITE

Calcined Dolomite or Flux Dolomite is the name given to the quicklime formed from calcining a natural dolomitic limestone that contains nearly an equal molar weight percentage of calcium oxide to magnesium oxide.

Dolomitic quicklime is the name given to the quicklime formed from calcining a natural dolomitic limestone that contains nearly an equal molar weight percentage of calcium oxide to magnesium oxide. Ideally, this quicklime would contain 56% calcium oxide, 40% magnesium oxide, and 4% other major lime impurities such as iron oxide, aluminum oxide, silicon dioxide, and sulfur.

IDENTIFICATION
Chemical name: Calcium magnesium oxide
Product name(s): : InjectoLimeTM Pebble Lime-Large, Pebble Lime-Small, Pebble
Lime-Rescreened, Mini Pebble, Pebble Lime, Rice, Fines,
Pulverized Lime, Dolopel, Dolopel Fines, HD Dolopel

Formula: MgO · CaO

Molecular Weight 96.38



Process The production of high calcium quicklime (magnesium oxide) requires a large amount of heat, which is generated in the kiln environment. The quarried and sized high magnesium limestone travels through a rotary kiln and is subjected to these high temperatures where the calcium carbonate begins to dissociate with the resultant formation of magnesium oxide. The minimum temperature for the dissociation of calcium carbonate is 1648°F (898°C). For practical production purposes, however, the kiln temperature range is from an initial temperature of about 1750°F (954°C) to a final temperature of about 1950°F (1066°C). These temperatures can vary dependent upon the nature of the limestone being calcined.



"Dolomitic" Limestone Calcination:
CaCO3 o MgCO3 + Heat ---> CaO o MgO + 2CO2



Content Percentage MgO- 35%
CaO- 55%
SiO2- 2%
R2O3- 2%

Hydrated Lime/Slaked Lime/Calcium Hydroxide

Hydrated Lime (or calcium hydroxide, or slaked lime) is usually a dry powder resulting from the controlled slaking of quicklime with water. The exothermic or released heat of reaction is captured and used to evaporate the excess slaking water.

Hydrated Lime is a chemical, with chemical formula Ca(OH)2 {Calcium Hydroxide}. Hydrated Lime is also known as Slaked Lime. It is white and in powder form with Ca(OH)2 contents varying from 96% to 70%.

IDENTIFICATION
Chemical name: Calcium hydroxide
Product name(s): Hydrated Lime, Industrial Hydrate

Formula: Ca(OH)2

Molecular Weight 74.08

Material Uses . Water Treatment Plant
. Effluent Treatment Plant
. pH Control
. Paint Industries
. Petroleum refining Industries
. Food Industries
. Leather Industry
. Paper Industry
. Pesticides
. Fertilizers
. Metallurgical Industries (Copper, Aluminum, Steel, Iron, etc)
. Marble/Granite Cutting
. Glass Industry
. Pharmaceutical Industry
. Cement paints
. Bleaching Powder
. Di Calcium Phosphate manufacturing
. Rubber Industry
. Road making and construction
. Sugar Industries



Specification of Hydrated Lime - Hydrated Lime/Slaked Lime/Calcium Hydroxide

Calcium Hydroxide
Ca(OH)2
96%
92%
90%
85%
80%
75%
70%

Calcium Oxide
CaO
72.5%
69.5%
68%
64%
60.5%
56.7%
52.9%

Calcium Carbonate
CaCO3
0.5%
1%
2%
4%
6%
8%
12%

Magnesium Oxide
MgO
0.4%
0.4%
0.4%
0.4%
1%
1%
1%

Acid Insoluble
SiO2
0.1 %
0.2%
0.4%
1.2%
2.5%
4%
6%

Alumina
Al2O3
0.03%
0.03%
0.05%
0.10%
0.15%
0.20%
0.25%

Iron
Fe2O3
0.03%
0.03%
0.05%
0.10%
0.15%
0.20%
0.25%

Moisture
0.2%
0.3%
0.5%
0.5%
0.5%
0.5%
0.5%

Mesh
(BSS)
400
375
250
200
175
150
150

CALCINED LIME

Calcined Lime (or calcium oxide, or burnt lime), is obtained by calcining(controlled heating-time and temperature) limestone at temperatures above 900°C. This highly reactive product is essential to many industrial processes.

CaO (Calcium Oxide) is the chemical formula of quick lime, which is also called as calcined lime, burnt lime and unslaked lime.These are white and in lumps and powder in form with CaO contents varying from 90% to 80% and it reacts with water and heat is generated.



IDENTIFICATION

Chemical name: Calcium oxide



Product name(s): Steel Grade-Large, Steel Grade-Large Rescreened, Steel Grade-Small,
Steel Grade-Small Rescreened, Water Grade-Small, Water Grade-Small
Rescreened, Mini Pebble, Rice, PCC Grade-Large Rescreened, PCC
Grade-Small Rescreened, Hi Cal Fines, Pulverized Lime, Pulverized
Lime

Formula: CaO

Molecular Weight 56.08

Material Uses • Food Industries
• Paper Industry
• Paint Industries
• pH Control
• Metallurgical Industries (Copper, Aluminum, Steel, Iron, etc).
• Glass Industry
• Sugar Industries
• Construction,
• White Wash
• Agriculture to improve acidic soils
• Pollution control
• Making Autoclaved Aerated concrete (AAC) Blocks.



Process High calcium quicklime readily reacts with water to form hydrated lime. The reaction is highly exothermic and the process is known as "slaking". The reaction is usually carried out in a "slaker" (a specially designed mixer) which, through a process of rigorous mixing, makes certain that all of the quicklime has come into intimate contact with water and no unreacted quicklime remains. From a general viewpoint the hydrated lime produced can be in the form of dry hydrate, putty slurry, or "milk of lime".



Quick Lime specifications - Quick Lime/Calcined Lime/Burnt Lime/ Calcium Oxide

Calcium Oxide
CaO
85% to 90%
80% – 85%
85% – 90%

Calcium Carbonate
CaCO3
3%
5%
2%

Magnesium Oxide
MgO
1 %
1%
1%

Acid Insoluble
SiO2
3%
5%
3%

Alumina
Al2O3
0.1 %
0.1 %
0.1 %

Iron
Fe2O3
0.1 %
0.1 %
0.1 %

Chloride
Cl
Traces
Traces
Traces

Moisture


Mesh
(BSS)
Lumps
Lumps
Powder (200 Mesh)

Quicklime or Calcium Oxide

Inorganic compound, white or grayish white solid, chemical formula CaO, made by roasting limestone (calcium carbonate, CaCO3) until all the carbon dioxide (CO2) is driven off. One of the four most important basic chemical commodities, it is used as a refractory, as a flux in steel manufacture, as a CO2 absorbent, to remove contaminants from stack gases, to neutralize various acids, in pulp and paper, in insecticides and fungicides, in sewage treatment, and in the manufacture of glass, calcium carbide, and sodium carbonate. Adding water to lime yields calcium hydroxide (slaked lime, calcium hydrate, hydrated lime, or caustic lime), which is used in mortar, plasters, cements, whitewash, hide dehairing, and water softening and purification and as a source of other calcium salts.

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calcium oxide

calcium oxide, chemical compound, CaO, a colorless, cubic crystalline or white amorphous substance. It is also called lime, quicklime, or caustic lime, but commercial lime often contains impurities, e.g., silica, iron, alumina, and magnesia. It is prepared by heating calcium carbonate calcium carbonate, CaCO3, white chemical compound that is the most common nonsiliceous mineral. It occurs in two crystal forms: calcite, which is hexagonal, and aragonite, which is rhombohedral.. (e.g., limestone limestone, sedimentary rock wholly or in large part composed of calcium carbonate. It is ordinarily white but may be colored by impurities, iron oxide making it brown, yellow, or red and carbon making it blue, black, or gray. The texture varies from coarse to fine.in a special lime kiln to about 500°C; to 600°C;, decomposing it into the oxide and carbon dioxide. Calcium oxide is widely used in industry, e.g., in making porcelain and glass; in purifying sugar; in preparing bleaching powder bleaching powder, white or nearly white powder that is usually a mixture of calcium chloride hypochlorite, CaCl(OCl); calcium hypochlorite, Ca(OCl)2; and calcium chloride, CaCl2. , calcium carbide, and calcium cyanamide; in water softeners; and in mortars and cements. In agriculture it is used for treating acidic soils (liming liming (lim`ing), application to the soil of calcium in various forms, generally as ground limestone, but also as marl, chalk, . It is incandescent when heated to high temperatures; the Drummond light, or limelight, provides a brilliant white light by heating a cylinder of lime with the flame of an oxyhydrogen torch. Calcium oxide is a basic anhydride, reacting with water to form calcium hydroxide calcium hydroxide, Ca(OH)2, colorless crystal or white powder. It is prepared by reacting calcium oxide (lime) with water, a process called slaking, and is also known as hydrated lime or slaked lime. the link for more information. ; during the reaction (slaking) much heat is given off and the solid nearly doubles its volume.

Limestone

Limestone is a "chemical" sedimentary rock that is composed mostly of calcite (CaCO3) that precipitates from seawater. Limestone, the most common chemical sedimentary rock in Texas, is commonly white to gray. Because the dominant mineral is calcite, limestone reacts with a strong effervescence when tested using a dilute acid such as hydrochloric acid or vinegar. Groundwater is slightly acidic and, hence, slowly dissolves limestone. This process has produced the caves of Texas.

Variations of limestone include marl, a muddy limestone, and chalk, a limestone composed of microscopic calcareous algae and tiny shells of marine organisms. Limestone is common in the Hill Country and the Trans-Pecos of Texas. Limestone in Texas is quarried for cement, aggregate, and building stone. High-calcium-content limestone is used in water purification and sewage treatment.

The limestone sample in the Texas Rock Kit was collected in Travis County and is Cretaceous in age.